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Authors: Jianhui Ma, Yuke Geng, Hong Liu, Mengqi Zhang, Shujuan Liu, Chenyang Hao, Jian Hou, Youfu Zhang, Daijing Zhang, Weijun Zhang, Xueyong Zhang and Tian Li.
Journal of Integrative Plant Biology (2023)
Abstract: "Drought is a major environmental stress limiting global wheat (Triticum aestivum) production. Exploring drought tolerance genes is important for improving drought adaptation in this crop. Here, we cloned and characterized TaTIP41, a novel drought tolerance gene in wheat. TaTIP41 is a putative conserved component of target of rapamycin (TOR) signaling, and the TaTIP41 homoeologs were expressed in response to drought stress and abscisic acid (ABA). The overexpression of TaTIP41 enhanced drought tolerance and the ABA response, including ABA-induced stomatal closure, while its downregulation using RNA interference (RNAi) had the opposite effect. Furthermore, TaTIP41 physically interacted with TaTAP46, another conserved component of TOR signaling. Like TaTIP41, TaTAP46 positively regulated drought tolerance. Furthermore, TaTIP41 and TaTAP46 interacted with type-2A protein phosphatase (PP2A) catalytic subunits, such as TaPP2A-2, and inhibited their enzymatic activities. Silencing TaPP2A-2 improved drought tolerance in wheat. Together, our findings provide new insights into the roles of TaTIP41 and TaTAP46 in the drought tolerance and ABA response in wheat, and their potential application in improving wheat environmental adaptability."
Authors: Gustavo Ravelo-Ortega, Jesús Salvador López-Bucio and José López-Bucio.
In book: "Mitigation of Plant Abiotic Stress by Microorganisms" (2022)
Abstract: "Microorganisms are integral components of plants for adaptation and surveillance to an ever-changing biosphere. Bacterial cell-to-cell signaling is achieved through biosynthesis, release, and perception of small molecules, which include the N-acyl-l-homoserine lactones (AHLs) and cyclodipeptides. Roots can recognize their prokaryotic partners to modulate waving and skewing and promote branching and absorptive potential. Such reciprocal signaling is achieved by two classes of amino lipids from the plant side, namely, alkamides and N-acyl ethanolamines (NAEs) that behave as structural mimics of AHLs. Abscisic acid (ABA), a canonical phytohormone orchestrating stress adaptation, has been found recently to act not only in rhizobacteria-mediated adaptation to abiotic stress, but also in the decodification of quorum-sensing signaling through cross talk with target of rapamycin (TOR) kinase. Understanding the specific mechanisms of the root adaptive and behavioral traits influenced by prokaryotes should help manage agriculture more appropriately in the long term."
Authors: Yoshiaki Kamiyama, Sotaro Katagiri and Taishi Umezawa.
Plants (2021)
Abstract: "Reversible phosphorylation is a major mechanism for regulating protein function and controls a wide range of cellular functions including responses to external stimuli. The plant-specific SNF1-related protein kinase 2s (SnRK2s) function as central regulators of plant growth and development, as well as tolerance to multiple abiotic stresses. Although the activity of SnRK2s is tightly regulated in a phytohormone abscisic acid (ABA)-dependent manner, recent investigations have revealed that SnRK2s can be activated by group B Raf-like protein kinases independently of ABA. Furthermore, evidence is accumulating that SnRK2s modulate plant growth through regulation of target of rapamycin (TOR) signaling. Here, we summarize recent advances in knowledge of how SnRK2s mediate plant growth and osmotic stress signaling and discuss future challenges in this research field."
Authors: Linxuan Li, Tingting Zhu, Yun Song, Li Feng, Essam Ali Hassan Farag and Maozhi Ren.
Frontiers in Plant Science (2021)
Abstract: "ABSCISIC ACID INSENSITIVE5 (ABI5) is an important regulator of abscisic acid (ABA) signaling pathway involved in regulating seed germination and postgerminative growth in Arabidopsis, which integrates various phytohormone pathways to balance plant growth and stress responses. However, the transcriptional regulatory mechanisms underlying ABI5 and its interacting proteins remain largely unknown. Here, we found that inhibition of AtTOR could increase ABA content by up-regulating the expression levels of ABA biosynthesis-related genes, and thus activated the expression of ABA-responsive genes. Pharmacological assay showed that abi5-1 mutant was insensitive to TOR inhibitor AZD8055, whereas AtABI5 overexpression lines were hypersensitive to AZD8055 in Arabidopsis. Biochemical interaction assays demonstrated that ABI5 physically interacted with the RIBOSOMAL S6 KINASE2 (S6K2) protein in plant cell. S6K2 positively regulated ABA responses during seedling growth and upregulated ABA-responsive genes expression. Furthermore, genetic and physiological analysis indicated that AtS6K2 overexpression lines enhanced resistance to drought treatment while AtS6K2 interference lines were sensitive to drought. These results indicated that AtABI5 interacted with AtS6K2 to positively modulate ABA responses during seedling growth and shed light on a underlying mechanism of the crosstalk between TOR and ABA signaling pathways in modulating seedling growth in Arabidopsis."
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Authors: Borja Belda-Palazón, Mónica Costa, Tom Beeckman, Filip Rolland and Elena Baena-González.
PNAS (2022)
Abstract: "The phytohormone abscisic acid (ABA) promotes plant tolerance to major stresses such as drought, partly by modulating growth through poorly understood mechanisms. Here, we show that ABA-triggered repression of cell proliferation in the Arabidopsis thaliana root meristem relies on the swift subcellular relocalization of SNF1-RELATED KINASE 1 (SnRK1). Under favorable conditions, the SnRK1 catalytic subunit, SnRK1α1, is enriched in the nuclei of root cells, and this is accompanied by normal cell proliferation and meristem size. Depletion of two key drivers of ABA signaling, SnRK2.2 and SnRK2.3, causes constitutive cytoplasmic localization of SnRK1α1 and reduced meristem size, suggesting that, under nonstress conditions, SnRK2s promote growth by retaining SnRK1α1 in the nucleus. In response to ABA, SnRK1α1 translocates to the cytoplasm, and this is accompanied by inhibition of target of rapamycin (TOR), decreased cell proliferation, and reduced meristem size. Blocking nuclear export with leptomycin B abrogates ABA-driven SnRK1α1 relocalization to the cytoplasm and ABA-elicited inhibition of TOR. Furthermore, fusing SnRK1α1 to an SV40 nuclear localization signal leads to defective ABA-dependent TOR repression. Altogether, we demonstrate that SnRK2-dependent changes in SnRK1α1 subcellular localization are crucial for inhibiting TOR and root growth in response to ABA. Rapid relocalization of central regulators such as SnRK1 may represent a general strategy of eukaryotic organisms to respond to environmental changes."
Authors: Borja Belda-Palazón, Mónica Costa, Tom Beeckman, Filip Rolland and Elena Baena-González.
bioRxiv (2021)
Abstract: "The phytohormone abscisic acid (ABA) promotes plant tolerance to major stresses like drought, partly by modulating plant growth and development. However, the underlying mechanisms are poorly understood. Here, we show that cell proliferation in the Arabidopsis thaliana root meristem is controlled by the interplay between three kinases, SNF1-RELATED KINASE 2 (SnRK2), the main driver of ABA signaling, the SnRK1 energy sensor, and the growth-promoting TARGET OF RAPAMYCIN (TOR) kinase. Under favorable conditions, the SnRK1α1 catalytic subunit is enriched in the nuclei of root meristematic cells and this is accompanied by normal cell proliferation and meristem size. Depletion of SnRK2s in a snrk2.2 snrk2.3 double mutant causes constitutive cytoplasmic localization of SnRK1α1 and a reduction in meristem size, suggesting that, under non-stress conditions, SnRK2s enable growth by retaining SnRK1α1 in the nucleus. In response to elevated ABA levels, SnRK1α1 translocates to the cytoplasm and this is accompanied by inhibition of TOR, decreased cell proliferation and meristem size. Blocking nuclear export with leptomycin B abrogates ABA-driven SnRK1α1 relocalization to the cytoplasm and the inhibition of TOR. Fusion of SnRK1α1 to an SV40 nuclear localization signal leads to defective TOR repression in response to ABA, demonstrating that SnRK1α1 nuclear exit is a premise for this repression. Finally, the SnRK2-dependent changes in SnRK1α1 subcellular localization are specific to the proliferation zone of the meristem, underscoring the relevance of this mechanism for growth regulation."
Authors: Björn Heinemann and Tatjana M. Hildebrandt.
Journal of Experimental Botany (2021)
Abstract: "The adaptation of plant metabolism to abiotic stress involves profound changes in amino acid metabolism. Unfavorable environmental conditions often lead to an impairment of photosynthesis. In response to the resulting lack of energy, plants activate respiratory pathways that use amino acids as alternative substrates. This review highlights recent progress in understanding these amino acid oxidation pathways, their regulation during stress, and the role of amino acids as signaling molecules. We present an updated map of the degradation pathways for lysine and the branched-chain amino acids including the last missing step in plant lysine catabolism, which has recently been identified, and several new steps involved in the degradation of leucine, isoleucine, and valine. The adaptation of amino acid metabolism to energy deprivation is mediated by the balance between TOR and SnRK signaling. The coordinated induction of several catabolic pathways during starvation is achieved by SnRK1 kinase via formation of a ternary complex including bZIP transcription factors. Recent findings indicate that some amino acids might act as TOR activators and thus promote a shift from catabolic to anabolic pathways. The metabolism of the sulfur containing amino acid cysteine is highly interconnected with TOR and SnRK signaling. Mechanistic details have recently been elucidated for cysteine signaling during the abscisic acid dependent drought response. Local cysteine synthesis triggers abscisic acid production and in addition, cysteine degradation produces the gaseous messenger hydrogen sulfide, which promotes stomatal closure via protein persulfidation. Amino acid signaling in plants is still an emerging topic with potential for fundamental discoveries."
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