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Authors: Chunmei Zhong, Barunava Patra, Yi Tang, Xukun Li, Ling Yuan and Xiaojing Wang.
Journal of Experimental Botany (2021)
Abstract: "Seed germination is regulated by multiple phytohormones, including Gibberellins (GAs) and Brassinosteroids (BRs); however, the molecular mechanism underlying GA and BR co-induced seed germination is not well elucidated. We demonstrated that BRs induce seed germination through promoting testa and endosperm rupture in Arabidopsis. BRs promote cell elongation, rather than cell division, at the hypocotyl-radicle transition region of embryonic axis during endosperm rupture. Two key basic helix-loop-helix transcription factors (TFs) in the BR signaling pathway, HBI1 and BEE2, are involved in the regulation of endosperm rupture. Expression of HBI1 and BEE2 was induced in response to BR and GA treatment. In addition, HBI1 or BEE2 overexpressing Arabidopsis plants are less sensitive to the BR biosynthesis inhibitor, brassinazole, and the GA biosynthesis inhibitor, paclobutrazol. HBI1 and BEE2 promote endosperm rupture and seed germination by directly regulating the GA-Stimulated Arabidopsis 6 (GASA6) gene. Expression of GASA6 was altered in Arabidopsis overexpressing HBI1, BEE2, or SRDX-repressor forms of the two TFs. In addition, HBI1 interacts with BEE2 to synergistically activate GASA6 expression. Our findings define a new role for GASA6 in GA and BR signaling and reveal a regulatory module that controls GA and BR co-induced seed germination in Arabidopsis."
Authors: Annelie Carlsbecker and Frauke Augstein.
Journal of Experimental Botany (2021)
Abstract: "Secondary growth generates wood, which constitutes most of the plant biomass. Despite considerable efforts over the last decade to uncover the genetic and molecular regulation of the vascular cambium, there is still much to learn about how it produces wood (xylem) inward and bast (phloem) outward. Ben-Targem et al. (2021) now provide novel insight into how the hormones auxin and gibberellic acid (GA) govern the activity of the cambium, promoting a transition from formation of equal amounts of xylem and phloem to a stage where xylem formation dominates phloem in Arabidopsis hypocotyls, resembling wood formation in trees."
Authors: Zhaoxia Sun, Xinfang Wang, Ronghua Liu, Wei Du, Mingchuan Ma, Yuanhuai Han, Hongying Li, Longlong Liu and Siyu Hou.
BMC Plant Biology (2021)
Abstract: "Background - Tartary buckwheat is an important minor crop species with high nutritional and medicinal value and is widely planted worldwide. Cultivated Tartary buckwheat plants are tall and have hollow stems that lodge easily, which severely affects their yield and hinders the development of the Tartary buckwheat industry. Methods - Heifeng No. 1 seeds were treated with ethylmethanesulfonate (EMS) to generate a mutant library. The dwarf mutant ftdm was selected from the mutagenized population, and the agronomic characteristics giving rise to the dwarf phenotype were evaluated. Ultra-fast liquid chromatography-electrospray ionization tandem mass spectrometry (UFLC-ESI–MS/MS) was performed to determine the factors underlying the different phenotypes between the wild-type (WT) and ftdm plants. In addition, RNA sequencing (RNA-seq) was performed via the HiSeq 2000 platform, and the resulting transcriptomic data were analysed to identify differentially expressed genes (DEGs). Single-nucleotide polymorphism (SNP) variant analysis revealed possible sites associated with dwarfism. The expression levels of the potential DEGs between the WT and ftdm mutant were then measured via qRT-PCR and fragments per kilobase of transcript per million mapped reads (FPKM). Result - The plant height (PH) of the ftdm mutant decreased to 42% of that of the WT, and compared with the WT, the mutant and had a higher breaking force (BF) and lower lodging index (LI). Lower GA4 and GA7 contents and higher contents of jasmonic acid (JA), salicylic acid (SA) and brassinolactone (BR) were detected in the stems of the ftdm mutant compared with the WT. Exogenous application of GAs could not revert the dwarfism of the ftdm mutant. On the basis of the transcriptomic analysis, 146 homozygous SNP loci were identified. In total, 12 DEGs with nonsynonymous mutations were ultimately identified, which were considered potential candidate genes related to the dwarf trait. When the sequences of eight genes whose expression was downregulated and four genes whose expression was upregulated were compared, SKIP14, an F-box protein whose sequence is 85% homologous to that of SLY1 in Arabidopsis, presented an amino acid change (from Ser to Asn) and was expressed at a lower level in the stems of the ftdm mutant compared with the WT. Hence, we speculated that this amino acid change in SKIP14 resulted in a disruption in GA signal transduction, indirectly decreasing the GA content and downregulating the expression of genes involved in GA biosynthesis or the GA response. Further studies are needed to determine the molecular basis underlying the dwarf phenotype of the ftdm mutant. Conclusion - We report a Tartary buckwheat EMS dwarf mutant, ftdm, suitable for high-density planting and commercial farming. A significant decrease in GA4 and GA7 levels was detected in the ftdm mutant, and 12 DEGs expressed in the stems of the ftdm mutant were selected as candidates of the dwarfing gene. One nonsynonymous mutation was detected in the SKIP14 gene in the ftdm mutant, and this gene had a lower transcript level compared with that in the WT."
Authors: Wenguan Zhou, Yingzeng Yang, Chuan Zheng, Xiaofeng Luo, Umashankar Chandrasekaran, Han Yin, Feng Chen, Yongjie Meng and Lei Chen and Kai Shu.
Environmental and Experimental Botany (2021)
Highlights: • In this study, we demonstrated that the flooding stress reduces soybean seed germination through decreasing the catabolism from triacylglycerol to sugars, changing the phytohormones (ABA and GA) levels, and promoting anaerobic respiration and then ethanol accumulation.
Abstract: "With global warming, flooding is becoming a serious natural abiotic stress in the past decades, which significantly influences plant growth and development, especially seed germination. However, the molecular mechanisms by which flooding stress repress land crops seed germination are largely unknown so far. Here, by using soybean (Glycine max), one of the most important oil crops worldwide, we report that flooding represses seed germination by mediating glycometabolism, anaerobic respiration and phytohormones biosynthesis related cascades. Phenotypic analysis showed that the flooding stress significantly decreases seed vigor and thus seed germination. Biochemical analysis demonstrated flooding leads to a decrease in several types of sugar contents during seed imbibition and an increase of cell conductivity as well as ethanol level, which remarkably inhibits seed germination. Subsequent transcriptomics and qPCR assays revealed that the expression levels of ABA (abscisic acid) and GA (gibberellin) biosynthesis/signaling and glycometabolism as well as anaerobic respiration related genes are consistent with the phenotypic and biochemical evidences. Furthermore, the exogenous sucrose or GA treatments can partially rescue the flooding or hypoxia-mediated repression of seed germination. Taken together, this study reveals that flooding stress impairs seed germination by decreasing sugar and phytohormones biosynthesis as well as promote anaerobic respiration."
Authors: Mahwish Ejaz, Stefano Bencivenga, Rafael Tavares, Max Bush and Robert Sablowski.
PNAS (2021)
Significance: A major issue in plant biology is how plants are shaped by the interaction between internal genetic programs—for example, those that form boundaries between leaves and the stem—and environmental signals such as light quality, which induces stem elongation in shade conditions. In many plant species, stem growth is suppressed during the vegetative phase, resulting in a compact whorl of leaves called a rosette. We show that the rosette habit of Arabidopsis is conferred by a gene involved in organ boundary formation, together with gibberellin hormone signaling, both of which antagonize genes that mediate organ growth in response to light. In this way, a common type of plant architecture results from localized inhibition of environmentally responsive growth.
Abstract: "The diversity and environmental plasticity of plant growth results from variations of repetitive modules, such as the basic shoot units made of a leaf, axillary bud, and internode. Internode elongation is regulated both developmentally and in response to environmental conditions, such as light quality, but the integration of internal and environmental signals is poorly understood. Here, we show that the compressed rosette growth habit of Arabidopsis is maintained by the convergent activities of the organ boundary gene ARABIDOPSIS THALIANA HOMEOBOX GENE 1 (ATH1) and of the gibberellin-signaling DELLA genes. Combined loss of ATH1 and DELLA function activated stem development during the vegetative phase and changed the growth habit from rosette to caulescent. Chromatin immunoprecipitation high-throughput sequencing and genetic analysis indicated that ATH1 and the DELLA gene REPRESSOR OF GA1-3 (RGA) converge on the regulation of light responses, including the PHYTOCHROME INTERACTING FACTORS (PIF) pathway, and showed that the ATH1 input is mediated in part by direct activation of BLADE ON PETIOLE (BOP1 and BOP2) genes, whose products destabilize PIF proteins. We conclude that an organ-patterning gene converges with hormone signaling to spatially restrict environmental responses and establish a widespread type of plant architecture."
Authors: Haiqi Zhang, Wei Han, Huibin Wang, Liu Cong, Rui Zhai, Chengquan Yang, Zhigang Wang and Lingfei Xu.
Research Square (2021)
Abstract: "Background: Parthenocarpy results in traits attractive to both consumers and breeders, and it overcomes the obstacle of self-incompatibility in the fruit set of horticultural crops, including pear (Pyrus bretschneideri). However, there is limited knowledge regarding the genetic and molecular mechanisms that regulate parthenogenesis. Results: Here, in a transcriptional comparison between pollination-dependent and GA4-induced parthenocarpy, PbCYP78A6 was identified and proposed as a candidate gene involved in parthenocarpy. PbCYP78A6 is similar to Arabidopsis thaliana CYP78A6 and is highly expressed in pear hypanthia. The increased PbCYP78A6 expression, as assessed by RT-qPCR, was induced by pollination and GA4 exposure. The ectopic overexpression of PbCYP78A6 contributed to parthenocarpic fruit production in tomato. The PbCYP78A6 expression coincided with fertilized and parthenocarpic fruitlet development and the expression of fruit development-related genes as assessed by cytological observations and RT-qPCR, respectively. PbCYP78A6 RNA interference and overexpression revealed that the gene is an upstream regulator of fruit development-related genes in pear. Conclusions: Our findings indicate that PbCYP78A6 plays a critical role in cell proliferation and provide insights into controlling parthenocarpy."
Authors: Yan Lv, Jinjing Pan, Houping Wang, Russel J. Reiter, Xia Li, Zongmin Mou, Jiemei Zhang, Zhengping Yao, Dake Zhao and Diqiu Yu.
Journal of Pineal Research (2021)
Abstract: "Seed germination, an important developmental stage in the life cycle of seed plants, is regulated by complex signals. Melatonin is a signaling molecule associated with seed germination under stressful conditions, although the underlying regulatory mechanisms are largely unknown. In this study, we showed that a low concentration (10 µM or 100 µM) of melatonin had no effect on seed germination, but when the concentration of melatonin increased to 500 µM or 1000 µM, seed germination was significantly inhibited in Arabidopsis. RNA sequencing analysis showed that melatonin regulated seed germination correlated to phytohormones abscisic acid (ABA), gibberellin (GA), and auxin. Further investigation revealed that ABA and melatonin synergistically inhibited seed germination, while GA and auxin antagonized the inhibitory effect of seed germination by melatonin. Disruption of the melatonin biosynthesis enzyme gene serotonin N‐acetyltransferase (SNAT), or N‐acetylserotonin methyltransferase (ASMT) promoted seed germination, while overexpression of ASMT inhibited seed germination. Taken together, our study sheds new light on the function and mechanism of melatonin in modulating seed germination in Arabidopsis."
Authors: Qian Liu, Kun Wu, Nicholas P. Harberd and Xiangdong Fu.
Molecular Plant (2021)
Excerpts: "Previous studies of Arabidopsis thaliana had discovered DELLA proteins (DELLAs), key components of the mechanism enabling the phytohormone gibberellin (GA) to promote growth. DELLAs are nuclear-localized growth inhibitors, and GA promotes plant growth by overruling their growth-inhibitory activity (Peng et al., 1997)."
"These advances had begun to solve the mystery of how GR genes work: GR alleles confer semi-dwarfism and increased yield through enhanced DELLA accumulation. Nevertheless, a major puzzle remained. The Rht-B1b and Rht-D1b open reading frames both contain premature stop codons shortly following the translation initiation AUG codon (Peng et al., 1999) (Figure 1A)."
"An important new report now provides a molecular test of this hypothesis (Van De Velde et al., 2021). First, expression of constructs designed to express tagged versions of the proposed N-terminally truncated Rht-B1b protein in transgenic wheat confers semi-dwarfism. Second, this expression generates a truncated Rht-B1b protein that is resistant to GA-promoted degradation, and presumably confers the observed semi-dwarf phenotype. Further experiments test an alternative hypothesis, that Rht-B1b and Rht-D1b semi-dwarfing phenotypes are conferred by a putative short peptide initiated at the original start codon and terminating at the premature mutant stop codons (Figure 1A)."
"The new knowledge that Rht-B1b and Rht-D1b encode N-terminally truncated DELLAs that are active in shoot but not in grain (Van De Velde et al., 2021) now makes possible new breeding strategies for improved GR varieties exhibiting enhanced NUE and grain yield (Figure 1B), thus reducing environmental impact."
Authors: Fanmiao Wang, Hideki Yoshida and Makoto Matsuoka.
Plant and Cell Physiology (2021)
Abstract: "Traditional breeding for high-yielding crops has mainly relied on the widespread cultivation of gibberellin (GA)-deficient semi-dwarf varieties, as dwarfism increases lodging resistance and allows for high nitrogen use, resulting in high grain yield. Although the adoption of semi-dwarf varieties in rice and wheat breeding brought big success to the “Green Revolution” in the 20th century, it consequently increased the demand for nitrogen-based fertilizer, which causes severe threat to ecosystems and sustainable agriculture. In order to make the “Green Revolution” truly green, it is necessary to develop new varieties with high nitrogen-use efficiency (NUE). Under this demand, research on NUE, mainly for rice, has made great strides in the last decade. This mini-review focuses on three aspects of recent epoch-making findings on rice breeding for high NUE. The first one on “NUE genes related to GA signaling” shows how promising it is to improve NUE in semi-dwarf Green Revolution Varieties. The second aspect centers around the nitrate transporter1.1B, NRT1.1B; studies have revealed a nutrient signaling pathway through the discovery of the nitrate-NRT1.1B-SPX4-NLP3 cascade. The last one is based on the recent finding that the Teosinte branched1, Cycloidea, Proliferating cell factor (TCP)-domain protein 19 underlies the genomic basis of geographical adaptation to soil nitrogen; OsTCP19 regulates the expression of a key transacting factor, DLT/SMOS2, which participates in the signaling of four different phytohormones, GA, auxin, brassinosteroid and strigolactone. Collectively, these breakthrough findings represent a significant step towards breeding high NUE rice in the future."
Authors: Inhye Lee, Eunsun Kim, Soobin Choi, Dayoung Kim, Wangyu Hong, Jungki Choi, Hyunmo Choi, Jimin Kim, Ganesh A. Sable, Kesavan Markkandan, Dongyeol Lim, Soon Ki Park, Soo Young Kim, Sumin Lee, and Moon-Soo Soh.
PNAS (2021)
Significance: Seed dormancy is an important developmental trait for plants, which ensures seed germination under more favorable spatiotemporal environments. A smoke compound, 3,4,5-trimethylfuran-2(5H)-one, which is called TMB for short, has been identified to inhibit seed germination in a still elusive way. Here, we presented several lines of evidence that TMB inhibits seed germination through the induction of physiological dormancy. Furthermore, by isolating TMB-resistant Arabidopsis mutants, we demonstrated that TMB RESISTANT1, encoding a Raf-like kinase, is critically required for the TMB-induced seed dormancy. These results suggest the presence of a smoke sensory pathway that takes part in the multiple layers of the dormancy regulatory network in higher plants.
Abstract: "Plants sense and integrate diverse stimuli to determine the timing for germination. A smoke compound, 3,4,5-trimethylfuran-2(5H)-one (trimethylbutenolide, TMB), has been identified to inhibit the seed germination of higher plants. To understand the mode of action, we examined various physiological and molecular aspects of the TMB-dependent inhibition of seed germination in Arabidopsis thaliana. The results indicated that the effect of TMB is due to the enhanced physiological dormancy, which is modulated by other dormancy regulatory cues such as after-ripening, stratification, and ABA/GA signaling. In addition, gene expression profiling showed that TMB caused genome-wide transcriptional changes, altering the expression of a series of dormancy-related genes. Based on the TMB-responsive physiological contexts in Arabidopsis, we performed mutant screening to isolate genetic components that underpin the TMB-induced seed dormancy. As a result, the TMB-RESISTANT1 (TES1) gene in Arabidopsis, encoding a B2 group Raf-like kinase, was identified. Phenotypic analysis of the tes1 mutant implicated that TES1 has a critical role in the TMB-responsive gene expression and the inhibition of seed germination. Taken together, we propose that plants have been equipped with a TMB sensory pathway through which the TMB induces the seed dormancy in a TES1-dependent way."
Authors: Yuanyuan Liu, Jing Wen, Xiaochun Ke, Jie Zhang, Xudong Sun, Chuntao Wang and Yongping Yang.
Protoplasma (2021)
Abstract: "Turnip is a member of the Brassica rapa species and is characterized by a swollen taproot that develops from the hypocotyl and part of the root. Gibberellins (GAs) are plant growth regulators involved in promoting cell elongation and play important roles in many aspects of plant growth and development. Interestingly, exogenous application of GA3 was found to significantly inhibit taproot formation in turnip. Moreover, endogenous GA contents decreased during the early developmental stages of taproot formation, suggesting that GA plays a negative role in taproot formation. We examined the anatomical structure of the taproot and found that lignification of the xylem cell wall was enhanced after treatment with GA3. Yeast two-hybrid assays suggested the occurrence of protein interactions between DELLAs and NACs in turnip. We also found that the expression of NAC-targeted genes involved in lignification of the secondary cell wall was significantly upregulated upon GA3 treatment. Taken together, these results supported the hypothesis that GA induced DELLA proteins degradation to release NAC proteins and induced xylem lignification, therefore inhibiting taproot formation, providing new insight into the molecular mechanism underlying turnip taproot formation."
Authors: Yi-Ran Ren, Qiang Zhao, Yu-Ying Yang, Rui Zhang, Xiao-Fei Wang, Tian-En Zhang, Chun-Xiang You, He-Qiang Huo and Yu-Jin Hao.
Plant Physiology (2021)
One-sentence summary: The BTB-TAZ protein interacts with and promotes ubiquitination and degradation of DELLA protein, thus regulating plant growth in response to nitrate.
Abstract: "Nitrate acts as a vital signal molecule in the modulation of plant growth and development. The phytohormones gibberellin (GA) is also involved in this process. However, the exact molecular mechanism of how nitrate and GA signaling pathway work together in regulating plant growth remains poorly understood. In this study, we found that a nitrate-responsive BTB/TAZ protein MdBT2 participates in regulating nitrate-induced plant growth in apple (Malus × domestica). Yeast two-hybridization, protein pull-down, and bimolecular fluorescence complementation (BiFC) assays showed that MdBT2 interacts with a DELLA protein MdRGL3a, which is required for the ubiquitination and degradation of MdRGL3a proteins via a 26S proteasome-dependent pathway. Furthermore, heterologous expression of MdBT2 partially rescued growth inhibition caused by overexpression of MdRGL3a in Arabidopsis. Taken together, our findings indicate that MdBT2 promotes nitrate-induced plant growth partially through reducing the abundance of the DELLA protein MdRGL3a."
Authors: Huayang Lv, Xiao Li, Hui Li, Yufeng Hu, Hanmei Liu, Shengjuan Wen, Yangping Li, Yinghong Liu, Huanhuan Huang, Guowu Yu, Yubi Huang and Junjie Zhang.
PLoS ONE (2021)
Abstract: "Proper development of the maize kernel is of great significance for high and stable maize yield to ensure national food security. Gibberellin (GA), one of the hormones regulating plant growth, is involved in modulating the development of maize kernels. Cellulose, one of the main components of plant cells, is also regulated by gibberellin. The mechanism of hormone regulation during maize grain development is highly complicated, and reports on GA-mediated modulation of cellulose synthesis during maize grain development are rare. Our study revealed that during grain growth and development, the grain length and bulk density of GA-treated corn kernels improved significantly, and the cellulose content of grains increased, while seed coat thickness decreased. The transcription factor basic region/leucine zipper motif 53 (bZIP53), which is strongly correlated with cellulose synthase gene 1 (CesA1) expression, was screened by transcriptome sequencing and the expression of the cellulose synthase gene in maize grain development after GA treatment was determined. It was found that bZIP53 expression significantly promoted the expression of CesA1. Further, analysis of the transcription factor bZIP53 determined that the gene-encoded protein was localized in the cell and nuclear membranes, but the transcription factor bZIP53 itself showed no transcriptional activation. Further studies are required to explore the interaction of bZIP53 with CesA1."
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Authors: Ming Zhong, Bingjie Zeng, Dongying Tang, Jiaxing Yang, Lina Qu, Jindong Yan, Xiaochuan Wang, Xin Li, Xuanming Liu and Xiaoying Zhao.
Molecular Plant (2021)
Abstract: "Light is a critical environmental cue that regulates a variety of diverse plant developmental processes. Cryptochrome 1 (CRY1) is the major photoreceptor mediating blue light-dependent photomorphogenic responses, such as inhibition of hypocotyl elongation. Gibberellin (GA) participates in repressing photomorphogenesis and promotes hypocotyl elongation. However, the antagonistic interaction between blue light and GA is not well understood. Here, we show that blue light represses GA-induced degradation of DELLA proteins (DELLAs), which are key negative regulators in the GA signaling pathway, via CRY1, thereby inhibiting the GA response during hypocotyl elongation. Data from our in vitro and in vivo biochemical analyses demonstrate that CRY1 physically interacts with GA receptors—GA INSENSITIVE DWARF 1 proteins (GID1s)—and DELLAs in a blue light-dependent manner. Furthermore, we show that CRY1 inhibits the association between GID1s and DELLAs. Genetically, CRY1 antagonizes the function of GID1s to repress the expression of cell elongation-related genes and hypocotyl elongation. Taken together, our findings demonstrate that CRY1 signals by stabilizing DELLAs through binding and inactivating GID1s and provide new insight into the mechanism by which blue light antagonizes the function of GA in photomorphogenesis."
Authors: Li Chen, Bin Lu, Liantao Liu, Wenjing Duan, Dan Jiang, Jin Li, Ke Zhang, Hongchun Sun, Yongjiang Zhang, Cundong Li and Zhiying Bai.
Plant Physiology and Biochemistry (2021)
Highlights: • 20 μM exogenous melatonin enhanced the cotton germination rate and hypocotyl length as well as the content of endogenous melatonin during seed germination. • Melatonin enhances salt tolerance in cotton seeds by regulating ABA and GA related genes. • Melatonin promoted seed germination by mediating the expression of plant hormone signal transduction genes. • Melatonin can reduce salt stress damage to the cotton seeds and promote seed germination.
Abstract: "Although previous studies have found that melatonin can promote seed germination, the phytohormone regulation mechanism by which exogenous melatonin mediates salt tolerance during cotton seed germination is still largely unknown. The effects of melatonin on germination traits and physiological parameters of GXM9 cotton seeds (Gossypium hirsutum L.) under three salt stress treatments (CK, germination of seeds pretreated with water alone; S, germination of seeds pretreated in 150 mM NaCl under salt stress; SM, germination of seeds pretreated in 20 μM melatonin under 150 mM NaCl solution) in the laboratory was investigated. The results showed that salt stress (150 mM) inhibited cotton seed germination and endogenous melatonin accumulation, and pretreatment with 20 μM exogenous melatonin enhanced the cotton germination rate and hypocotyl length as well as the content of endogenous melatonin during seed germination. This suggests that exogenous melatonin promotes seed germination from a morphological perspective. The contents of starch, α-amylase (EC3.3.1.1), β-galactosidase (EC3.2.1.23), abscisic acid (ABA), and gibberellin (GA) were determined simultaneously. The results showed that the α-amylase and β-galactosidase contents in the cotton seeds decreased by 56.97% and 20.18%, respectively, under salt stress compared with the control, while the starch content increased by 11.53% compared with the control at day 7. The ABA content increased by 25.18% and GA content decreased by 27.99% under salt stress compared with the control at 24 h. When exogenous melatonin was applied to the cotton seeds, the content of α-amylase and β-galactosidase increased by 121.77% and 32.76%, respectively, whereas the starch contents decreased by 13.55% compared with the S treatment at day 7. Similarly, the ABA content increased by 12.20% and the GA content increased by 4.77% at 24 h. To elucidate the molecular mechanism by which melatonin promotes seed germination under salt stress, the effects of ABA- and GA-related genes on plant hormone signal transduction were analyzed by quantitative real-time PCR and RNA sequencing. The results indicated that melatonin regulated the expression of ABA and GA genes in the plant signal transduction pathway, induced embryo root development and seed germination, and alleviated dormancy. The expression of the ABA signaling gene GhABF2 was up-regulated and GhDPBF2 was down-regulated, and the expression of GA signaling genes (e.g., GhGID1C and GhGID1B) was up-regulated by melatonin. In conclusion, melatonin enhances salt tolerance in cotton seeds by regulating ABA and GA and by mediating the expression of hormone-related genes in plant hormone signal transduction. This should help us to explore the regulatory mechanisms of cotton resistance and provide a foundation for the cultivation of new varieties."
Authors: Wenrong Tan, Qing Han, Yan Li, Feng Yang, Jiafeng Li, Pengxu Li, Xiumei Xu, Honghui Lin and Dawei Zhang.
New Phytologist (2021)
Abstract: "Trichome initiation and leaf growth are two critical developmental processes in the plant life cycle, which need to be optimized in accordance with developmental stages and immediate surroundings. To a large extent, this optimization is achieved by fine‐tuning of hormonal pathways, including the Gibberellins (GAs) pathway. However, the mechanism by which plants control GA homeostasis to optimize these two developmental processes is unknown. Here, we report HAT1, an HD‐ZIP II transcriptional factor, negatively regulates the GA‐mediated trichome initiation and cotyledon expansion. Both the transcript and protein levels of HAT1 are induced by GA, while increased HAT1, in return, suppresses GA biosynthesis and signaling, thus forming a negative feedback regulatory loop that controls GA homeostasis to fine‐tune trichome development and cotyledon expansion. We also find that HAT1 interacts with DELLAs, including GAI and RGA. GAI inhibits both the protein stability and the binding activity of HAT1 regarding to its target genes. Overexpression of HAT1 in della5 can totally suppress the enhanced trichome initiation and enlarged cotyledon of della5. Our findings demonstrate that HAT1 functions as a critical repressor to regulate the GA‐mediated trichome initiation and cotyledon growth; meanwhile they uncover a novel mechanism by which the plant regulates trichome initiation and cotyledon expansion through HAT1‐DELLA regulatory module under various GA concentrations."
Authors: Li-Jun Huang, Jianjun Luo, Yukun Wang and Ning Li.
Plant Signaling & Behavior (2021)
Abstract: "Rice tillering is an important characteristic that responds to both GA (gibberellin) and nitrogen-based fertilizers. How plants balance these two responses? A newly identified NGR5 (NITROGEN-MEDIATED TILLER GROWTH RESPONSE 5) protein reveals its important role in controlling the balance between GA-regulated dwarfism and nitrogen-regulated tillering. NGR5 directly interacts with PRC2 (Polycomb Repressive Complex 2) to form a repressive complex at the shoot branching inhibitory genes in nitrogen-dependent way, thereby repressing branching inhibitors and promoting tillering in response to nitrogen fertilizers. The GA receptor GID1 (GIBBERELLIN INSENSITIVE DWARF1) targets NGR5 for proteolysis by the 26S proteasome. The rice DELLA proteins of GA signaling way competitively inhibit GID1-NGR5 interaction, thereby protecting NGR5 from degradation and enhancing nitrogen-induced tiller number."
Authors: Zong-You Lv, Wen-Jing Sun, Rui Jiang, Jun-Feng Chen, Xiao Ying, Lei Zhang and Wan-Sheng Chen.
World Journal of Traditional Chinese Medicine (2021)
Abstract: "Until recently, many studies on the role of phytohormones in plant secondary metabolism focused on jasmonic acid (JA), salicylic acid (SA), gibberellins (GA), and abscisic acid (ABA). It is now clear that phytohormone-induced regulation of signaling occurs via regulation of the biosynthetic pathway genes at the transcriptional level or through posttranslational regulation, or an increase in secondary metabolite deposition (e.g., trichomes). Here, we summarize recent advances, updating the current reports on the molecular machinery of phytohormones JA, SA, GA, and ABA involved in plant secondary metabolites. This review emphasizes the differences and similarities among the four phytohormones in regulating various secondary metabolic biosynthetic pathways and also provides suggestions for further research."
Authors: Hagai Shohat, Hadar Cheriker, Himabindu Vasuki, Natanella Illouz-Eliaz, Shula Blum, Ziva Amsellem, Danuše Tarkowská, Asaph Aharoni, Yuval Eshed and David Weiss.
bioRxiv (2021)
Abstract: "Plants reduce transpiration to avoid dehydration during drought episodes by stomatal closure and inhibition of canopy growth. While abscisic acid (ABA) has a primary role in ‘drought avoidance’, previous studies suggest that gibberellin (GA), might also be involved. Here we show in tomato (Solanum lycopersicum) that shortage of water inhibited the expression of the GA biosynthesis genes GA20 oxidase1 (GA20ox1) and GA20ox2 and induced the GA-deactivating gene GA2ox7 in leaves and guard cells, resulting in reduced bioactive GA levels. Drought regulation of GA metabolism was mediated by ABA-dependent and independent pathways, and by the transcription factor DEHYDRATION RESPONSIVE ELEMENT BINDING (DREB), TINY1. Mutations in GA20ox1 and GA20ox2 reduced water loss due to the smaller canopy area. On the other hand, loss of GA2ox7 did not affect leaf size, but attenuated stomatal response to water deficiency; during soil dehydration, ga2ox7 plants closed their stomata and reduced transpiration later than WT, suggesting that ga2ox7 stomata are hyposensitive to soil dehydration. Together, the results suggest that drought-induced GA deactivation in guard cells contributes to stomatal closure at the early stages of soil dehydration, whereas inhibition of GA synthesis in leaves promotes mainly the long-term reduction in canopy growth to reduce transpiration area."
Authors: Limin Wang, Boyang Yu, Yanan Zhao, Yongzhou Li, Jing Guo and YuanDi Zhu.
Acta Physiologiae Plantarum (2021)
Abstract: "Columnar apples are a labor saving and productive tree form that has long been of interest to apple breeders and producers. MdCo31, which encodes a putative 2OG-Fe(II) oxygenase, is a potential candidate gene involved in controlling the internode length of columnar growth of apple. In this study, a putative regulation in internode length was conducted by exogenous application of GA3 and paclobutrazol. The results showed that the MdCo31-GFP fusion protein was specifically localized in the cytoplasm. Heterologous over-expression of MdCo31 in tobacco produced stunted phenotypes with high chlorophyll content in leaves, and delayed the timing of seed germination and flowering. The over-expression tobacco plants were more sensitive to exogenous application of GA3 but insensitive to paclobutrazol, and their growth correlated to lower concentrations of endogenous GA1 and lower expression levels of the gibberellin-regulated family gene NtGASA6. The higher the MdCo31 expression levels were identified in more dwarf transformants with the shorter internodes. This research proposed that the decrease in endogenous GA1, resulting from high MdCo31 expression, induced dwarf phenotypes and shorted internodes, which indicated that MdCo31 is responded to gibberellins’ deficiency conferring the internodal growth of columnar apples."
Authors: Li Tai, Hong-Jin Wang, Xiao-Jing Xu, Wei-Hang Sun, Lan Ju, Wen-Ting Liu, Wen-Qiang Li, Jiaqiang Sun and Kun-Ming Chen
Journal of Experimental Botany (2021)
Abstract: "With the growth of the global population and the increasing frequency of natural disasters, crop yields must be steadily increased to enhance human adaptability to risks. Pre-harvest sprouting (PHS), a term mainly used to describe the phenomenon in which grains germinate on the mother plant directly before harvest, is a serious global problem for agricultural production. After domestication, the dormancy level of cultivated crops was generally lower than that of their wild ancestors. Although the shortened dormancy period likely improved the industrial performance of cereals such as wheat, barley, rice, and maize, the excessive germination rate has caused frequent PHS in areas with higher rainfall, resulting in great economic losses. Here, we systematically review the causes of PHS and its consequences, the major indicators and methods for PHS assessment, and emphasize the biological significance of PHS in crop production. Wheat quantitative trait loci functioning in the control of PHS are also comprehensively summarized in a meta-analysis. Finally, we use Arabidopsis as a model plant to develop more complete PHS regulatory networks for wheat. The integration of this information is conducive to the development of custom-made cultivated lines suitable for different demands and regions, and is of great significance for improving crop yields and economic benefits."
Authors: Jing Xiong, Xuanjun Feng, Weixiao Zhang, Xianqiu Wang, Yue Hu, Xuemei Zhang, Fengkai Wu, Wei Guo, Wubing Xie, Qingjun Wang, Jie Xu and Yanli Lu.
bioRxiv (2021)
Abstract: "Lateral organ boundaries domain (LBD) proteins are plant-specific transcription factors. Class I LBD members are widely reported to be pivotal for organ development, however, the role of class II members is unknown in cereal crops. Class II LBD proteins are distinguished from class I by the lack of a Gly-Ala-Ser (GAS) peptide and leucine-zipper-like coiled-coil domain, which is thought to be essential for protein dimerization. In this study, ZmLBD5 and ZmLBD33 form homo- and hetero-dimers, like class I members. At seedling stage, ZmLBD5 promoted biomass accumulation (shoot dry weight and root dry weight), root development (root length, root number, and root volume), and organ expansion (leaf area), while ZmLBD33 repressed these processes and display a dwarf phenotype. Both ZmLBD5 and ZmLBD33 displayed negative roles in drought tolerance mainly by increasing stomatal density and stomatal aperture. RNA sequencing, gene ontology enrichment analysis, and transient luciferase expression assays indicated that ZmLBD5 and ZmLBD33 are mainly involved in the regulation of the TPS-KS-GA2ox gene module, which comprises key enzymatic genes upstream of GA and ABA biosynthesis. GA1 content increased in ZmLBD5-overexpressing seedlings, while GA3 and abscisic acid content decreased in both transgenic seedlings. Consequently, exogenous GA1 or GA3 undoubtedly rescued the dwarf phenotype of ZmLBD33-overexpressing plants, with GA1 performing better. The study of ZmLBD5 and ZmLBD33 sheds light on the function of the class II LBD gene family in maize."
Authors: Mohammad Shah Jahan, Sheng Shu, Yu Wang, Md. Mahadi Hasan, Ahmed Abou El-Yazied, Nadiyah M. Alabdallah, Dina Hajjar, Muhammad Ahsan Altaf, Jin Sun and Shirong Guo.
Frontiers in Plant Science (2021)
Abstract: "Heat stress and abscisic acid (ABA) induce leaf senescence, whereas melatonin (MT) and gibberellins (GA) play critical roles in inhibiting leaf senescence. Recent research findings confirm that plant tolerance to diverse stresses is closely associated with foliage lifespan. However, the molecular mechanism underlying the signaling interaction of MT with GA and ABA regarding heat-induced leaf senescence largely remains undetermined. Herein, we investigated putative functions of melatonin in suppressing heat-induced leaf senescence in tomato and how ABA and GA coordinate with each other in the presence of MT. Tomato seedlings were pretreated with 100 μM MT or water and exposed to high temperature (38/28°C) for 5 days (d). Heat stress significantly accelerated senescence, damage to the photosystem and upregulation of reactive oxygen species (ROS), generating RBOH gene expression. Melatonin treatment markedly attenuated heat-induced leaf senescence, as reflected by reduced leaf yellowing, an increased Fv/Fm ratio, and reduced ROS production. The Rbohs gene, chlorophyll catabolic genes, and senescence-associated gene expression levels were significantly suppressed by MT addition. Exogenous application of MT elevated the endogenous MT and GA contents but reduced the ABA content in high-temperature-exposed plants. However, the GA and ABA contents were inhibited by paclobutrazol (PCB, a GA biosynthesis inhibitor) and sodium tungstate (ST, an ABA biosynthesis inhibitor) treatment. MT-induced heat tolerance was compromised in both inhibitor-treated plants. The transcript abundance of ABA biosynthesis and signaling genes was repressed; however, the biosynthesis genes MT and GA were upregulated in MT-treated plants. Moreover, GA signaling suppressor and catabolic gene expression was inhibited, while ABA catabolic gene expression was upregulated by MT application. Taken together, MT-mediated suppression of heat-induced leaf senescence has collaborated with the activation of MT and GA biosynthesis and inhibition of ABA biosynthesis pathways in tomato."
Authors: I. S. Sukhikh, V. J. Vavilova, A. G. Blinov and N. P. Goncharov.
Russian Journal of Genetics (2021)
Abstract: "The review is devoted to the description of allelic variants of Rht genes and their effect on the traits associated with the growth, development, and yield of wheat plants. The effect of Rht genes on the growth and development of wheat plants through DELLA proteins is considered. A new classification of wheat plants by the height (stem length) based on the presence/absence of strictly defined alleles of Rht genes determined by molecular genetic methods in their genotypes is proposed."
Authors: Backiyarani Suthanthiram, Sasikala Rajendran, Sharmiladevi Simeon and Uma Subbaraya.
Research Square (2021)
Abstract: "Banana, one of the most important staple, delicious fruit among global consumers is highly sterile owing to natural parthenocarpy. Identification of genetic factors responsible for parthenocarpy would facilitate the conventional breeders to improve the seeded accessions. We have constructed Protein-protein interaction (PPI) network through mining differentially expressed genes and the genes used for transgenic studies with respect to parthenocarpy. Based on the topological and pathway enrichment analysis of proteins in PPI network, 12 candidate genes were shortlisted. By exploring the PPI of candidate genes from the putative network, we postulated a putative pathway that bring insights into the significance of cytokinin mediated CLV-WUSHEL signaling pathway in addition to gibberellin mediated auxin signaling pathway in parthenocarpy. Further validation of candidate genes in seeded and seedless accession of Musa spp using qRT-PCR put forward AGL8, MADS16, IAA (GH3.8), RGA1, EXPA1, GID1C, HK2 and BAM1 as possible target genes in natural parthenocarpy. In contrary, expression profile of ACLB-2 and ZEP is anticipated to highlight the difference in artificially induced and natural parthenocarpy. Our analysis is the first attempt to identify candidate genes and to hypothesize a putative mechanism that bridges the gaps in understanding natural parthenocarpy through protein-protein interaction network."
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