Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Weifeng Chen, Zhengcao Xiao, Yule Wang, Jinxiao Wang, Rui Zhai, Kui Lin-Wang, Richard Espley, Fengwang Ma and Pengmin Li.

Horticulture Research (2021)

Abstract: "Flavonoids play important roles in regulating plant growth and development. In this study, three kaempferol 3-O-glycosides were identified and mainly accumulated in flowers but not in leaves or fruits of Malus. In Malus, flower petal color is normally white, but some genotypes have red flowers containing anthocyanin. Anthocyanin biosynthesis appears to be in competition with kaempferol 3-O-glycosides production and controlled by the biosynthetic genes. The white flower Malus genotypes had better-developed seeds than the red flower genotypes. In flowers, the overexpression of MYB10 in Malus domestica enhanced the accumulation of anthocyanin, but decreased that of kaempferol 3-O-glycosides. After pollination the transgenic plants showed slower pollen tube growth and fewer developed seeds. Exogenous application of different flavonoid compounds suggested that kaempferol 3-O-glycosides, especially kaempferol 3-O-rhamnoside, regulated pollen tube growth and seed set rather than cyanidin or quercetin 3-O-glycosides. It was found that kaempferol 3-O-rhamnoside might regulate pollen tube growth through effects on auxin, the Rho of plants (ROP) GTPases, calcium and the phosphoinositides signaling pathway. With the inhibition of auxin transport, the transcription levels of Heat Shock Proteins (HSPs) and ROP GTPases were downregulated while the levels were not changed or even enhanced when blocking calcium signaling, suggesting that HSPs and ROP GTPases were downstream of auxin signaling, but upstream of calcium signaling. In summary, kaempferol glycoside concentrations in pistils correlated with auxin transport, the transcription of HSPs and ROP GTPases, and calcium signaling in pollen tubes, culminating in changes to pollen tube growth and seed set."

Authors: Huaying Ma, Tuo Yang, Yu Li, Jie Zhang, Ting Wu, Tingting Song, Yuncong Yao and Ji Tian.

The Plant Cell (2021)

Abstract: "Anthocyanin pigments contribute to plant coloration and are valuable sources of antioxidants in the human diet as components of fruits and vegetables. Their production is known to be induced by light in (Malus domestica) apple fruit; however, the underlying molecular mechanism responsible for early-stage light-induced anthocyanin biosynthesis remains unclear. Here, we identified an ERF (ethylene response factor) protein, ERF109, involved in light-induced anthocyanin biosynthesis and found that it promotes coloration by directly binding to anthocyanin-related gene promoters. Promoter::GUS (β-glucuronidase) reporter analysis and Hi-C sequencing showed that a long non-coding RNA (lncRNA), MdLNC499, located upstream from MdERF109, induces the expression of MdERF109. A W-box cis-element in the MdLNC499 promoter was found to be regulated by a transcription factor, MdWRKY1. Transient expression in apple fruit and stable transformation of apple calli allowed us to reconstruct a MdWRKY1-MdLNC499-MdERF109 transcriptional cascade in which MdWRKY1 is activated by light to increase the transcription of MdLNC499, which in turn induces MdERF109. The MdERF109 protein induces the expression of anthocyanin-related genes and the accumulation of anthocyanins in the early stages of apple coloration. Our results provide a platform for better understanding the various regulatory mechanisms involved in light-induced apple fruit coloration."

Authors: Amy M. LaFountain and Yao‐Wu Yuan.

New Phytologist (2021)

Abstract: "Anthocyanins play a variety of adaptive roles in both vegetative tissues and reproductive organs of plants. The broad functionality of these compounds requires sophisticated regulation of the anthocyanin biosynthesis pathway to allow proper localization, timing, and optimal intensity of pigment deposition. While it is well‐established that the committed steps of anthocyanin biosynthesis are activated by a highly conserved MYB‐bHLH‐WDR (MBW) protein complex in virtually all flowering plants, anthocyanin repression seems to be achieved by a wide variety of protein and small RNA families that function in different tissue types and in response to different developmental, environmental, and hormonal cues. In this review, we survey recent progress in the identification of anthocyanin repressors and the characterization of their molecular mechanisms. We find that these seemingly very different repression modules act through a remarkably similar logic, the so‐called "double negative logic". Much of the double‐negative regulation of anthocyanin production involves signal‐induced degradation or sequestration of the repressors from the MBW protein complex. We discuss the functional and evolutionary advantages of this logic design compared with simple or sequential positive regulation. These advantages provide a plausible explanation to why plants have evolved so many anthocyanin repressors."

Authors: Jingyu Zhang, Yuhao Cao, Jia Tang, Xujie He, Ming Li, Chen Li, Xiaolin Ren and Yuduan Ding.

Horticulturae (2023)

Abstract: "Gibberellins (GAs) are plant hormones indispensable in regulating the growth and development of fruits. Recent studies have shown that GAs play important roles in delaying horticultural crop ripening and senescence, enhancing the internal and external quality of horticultural crops and resistance to stress and disease. We reviewed the role of GAs in the postharvest physiology of fruits in recent years. GAs are closely related to their ability to retard fruit senescence. GAs could effectively improve fruit storage quality and significantly increase flesh hardness, reduce respiration intensity, inhibit the release of endogenous ethylene, and effectively inhibit fruit softening and ripening. It can also improve the intrinsic and extrinsic quality of fruit storage by improving fruit shape, regulating color, delaying the reduction of soluble solids, promoting sugar accumulation, and delaying vitamin loss. GAs also play a role in postharvest biotic and abiotic stress resistance. The GA treatment effectively reduces the cold damage index, reduces the production and accumulation of superoxide anion(O2−), improves the antioxidant capacity of fruits, and maintains the integrity of cell membranes during low-temperature storage. Moreover, GAs could effectively control some postharvest fruit diseases. In conclusion, GAs play an important role in the physiological regulation of postharvest fruits and have important application prospects in postharvest fruits."

Authors: Claudio Ponce, Nathalie Kuhn, Macarena Arellano, Alson Time, Salvatore Multari, Stefan Martens, Esther Carrera, Boris Sagredo, José Manuel Donoso and Lee A. Meisel.

Journal of Agriculture and Food Chemistry (2021) 

Abstract: "Color acquisition is one of the most distinctive features of fruit development and ripening processes. The color red is closely related to the accumulation of polyphenolic compounds, mainly anthocyanins, during sweet cherry fruit maturity. In non-climacteric fruit species like sweet cherry, the maturity process is mainly controlled by the phytohormone abscisic acid (ABA), though other hormones may also play a role. However, the coordinated stage-specific production of polyphenolic compounds and their relation with hormone content variations have not been studied in depth in sweet cherry fruits. To further understand the accumulation dynamics of these compounds (hormones and metabolites) during fruit development, two sweet cherry cultivars (“Lapins” and “Glenred”) with contrasting maturity timing phenotypes were analyzed using targeted metabolic analysis. The ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) approach revealed that phenolic acids, flavonols, and flavan-3-ols accumulated mainly until the straw-yellow stage in the early-maturing cultivar, while accumulation was mainly at the green stage in the mid-maturing cultivar, suggesting a cultivar-dependent stage-specific production of secondary metabolites. In the mid-maturing cultivar, anthocyanins were detected only from the red stage onward, whereas detection began at the pink stage in the early-maturing cultivar. ABA negatively correlated (p-value < 0.05) with the flavonols and flavan-3-ols in both cultivars. ABA and anthocyanin content increased at the same time in the early-season cultivar. In contrast, anthocyanins accumulated and the pink color initiation started several days after the ABA increase in the mid-maturing cultivar. Differential accumulation patterns of GA4, a ripening antagonizing hormone, between the cultivars could explain this difference. These results showed that both red-colored cultivars presented different accumulation dynamics of phenolic compounds and plant hormones during fruit development, suggesting underlying differences in the sweet cherry fruit color evolution."

Authors: Xiaobai Li, Yan Hong, Aaron Jackson and Fangqi Guo.

Scientific Reports (2021)

Abstract: "Blueberry is rich in anthocyanins which accumulate during fruit maturation. Previous studies mostly focus on their translational/transcriptional regulation, but usually underestimate their post-transcriptional regulation, e.g. small RNAs. This study aimed to identify sRNAs and their potential pathways associated with anthocyanin biosynthesis. During three typical phases of fruit maturation (green, pink, and blue), we investigated dynamic changes of sRNA by deep sequencing sRNA and examined the interaction of sRNAs with their target genes by degradome and RLM-PCR. During maturation, up-regulation of VcmiRNA156 and VcmiR393 resulted in down-regulation of VcSPLs and VcTIR1/AFBs, respectively. An important gene of anthocyanin biosynthesis, VcDFR, was substantially down-regulated at both the mRNA and protein levels, and potentially responded to regulation of VcSPLs and VcTIR1/AFBs. Additionally, indole acetic acid (IAA) and abscisic acid (ABA) were involved in the regulation of anthocyanin biosynthesis by interacting with VcmiR393-TIR1/AFBs and VcmiRNA319-VcMYBs respectively. This information provides another insight into blueberry anthocyanin biosynthesis."

Authors: Yicheng Wang, Zuolin Mao, Huiyan Jiang, Zongying Zhang, Nan Wang and Xuesen Chen.

Journal of Experimental Botany (2021)

Abstract: "The flavonoid content, which is an important indicator of the nutritional value of fruits and vegetables, directly determines the marketability of many fruit crops, including apple (Malus domestica). Brassinosteroids (BRs) are steroid hormones that affect flavonoid biosynthesis in plants, but the underlying regulatory mechanism remains unclear. In this study, treatments with brassinolide (the most active BR) and brassinazole (a BR biosynthesis inhibitor) respectively decreased and increased the flavonoid, anthocyanin, and proanthocyanidin (PA) contents in red-fleshed apple seedlings and calli. We subsequently demonstrated that a BZR family transcription factor (TF), MdBEH2.2, participates in BR-regulated flavonoid biosynthesis. Specifically, MdBEH2.2 inhibits the accumulation of flavonoids, anthocyanins, and PAs in apple seedlings; however, a brassinazole treatment can weaken the inhibitory effect. Additionally, we confirmed that a BR-induced MYB TF, MdMYB60, interacts with MdBEH2.2. The resulting MdBEH2.2–MdMYB60 complex further enhances the inhibitory effect of MdBEH2.2 or MdMYB60 on the transcription of structural genes. These results imply that brassinolide decreases flavonoid contents through the MdBEH2.2–MdMYB60 regulatory module. Our findings further clarify the molecular mechanism mediating the regulation of flavonoid biosynthesis by BR signals in horticultural crops."