Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Zhen Zhang, Cui Chen, Changyue Jiang, Hong Lin, Yuhui Zhao and Yinshan Guo.

Horticulture Research (2024)

Abstract: "Wounding stress induces the biosynthesis of various secondary metabolites in plants, including anthocyanin. However, the underlying molecular mechanism remains elusive. Here, we reported that a transcription factor, VvWRKY5, promotes wounding-induced anthocyanin accumulation in grape (Vitis vinifera). Biochemical and molecular analyses demonstrated that wounding stress significantly increased anthocyanin content, and VvMYBA1 plays an essential role in this process. VvWRKY5 could interact with VvMYBA1 and amplify the activation effect of VvMYBA1 on its target gene VvUFGT. The transcript level of VvWRKY5 was notably induced by wounding treatment. Moreover, our data demonstrated that VvWRKY5 could promote the synthesis of jasmonic acid (JA), a phytohormone that acts as a positive modulator in anthocyanin accumulation, by directly binding to the W-box element in the promoter of the JA biosynthesis-related gene VvLOX and enhancing its activities, and this activation was greatly enhanced by the VvWRKY5-VvMYBA1 protein complex. Collectively, our findings show that VvWRKY5 plays crucial roles in wounding-induced anthocyanin synthesis in grape and elucidates the transcriptional regulatory mechanism of wounding-induced anthocyanin accumulation."

Authors: Meiying Liu, Chaoran Wang, Hongliang Ji, Maoxiang Sun, Tongyu Liu, Jiahao Wang, Hui Cao and Qinggang Zhu.

Frontiers in Plant Science (2024)

Abstract: "In recent years, the ethylene-mediated ripening and softening of non-climacteric fruits have been widely mentioned. In this paper, recent research into the ethylene-mediated ripening and softening of non-climacteric fruits is summarized, including the involvement of ethylene biosynthesis and signal transduction. In addition, detailed studies on how ethylene interacts with other hormones to regulate the ripening and softening of non-climacteric fruits are also reviewed. These findings reveal that many regulators of ethylene biosynthesis and signal transduction are linked with the ripening and softening of non-climacteric fruits. Meanwhile, the perspectives of future research on the regulation of ethylene in non-climacteric fruit are also proposed. The overview of the progress of ethylene on the ripening and softening of non-climacteric fruit will aid in the identification and characterization of key genes associated with ethylene perception and signal transduction during non-climacteric fruit ripening and softening."

Authors: Yi-Wen Wang and Savithri U. Nambeesan.

BMC Plant Biology (2024)

Abstract: "Background - Blueberry fruit exhibit atypical climacteric ripening with a non-auto-catalytic increase in ethylene coincident with initiation of ripening. Further, application of ethephon, an ethylene-releasing plant growth regulator, accelerates ripening by increasing the proportion of ripe (blue) fruit as compared to the control treatment. To investigate the mechanistic role of ethylene in regulating blueberry ripening, we performed transcriptome analysis on fruit treated with ethephon, an ethylene-releasing plant growth regulator. Results - RNA-Sequencing was performed on two sets of rabbiteye blueberry (‘Powderblue’) fruit: (1) fruit from divergent developmental stages; and (2) fruit treated with ethephon, an ethylene-releasing compound. Differentially expressed genes (DEGs) from divergent developmental stages clustered into nine groups, among which cluster 1 displayed reduction in expression during ripening initiation and was enriched with photosynthesis related genes, while cluster 7 displayed increased expression during ripening and was enriched with aromatic-amino acid family catabolism genes, suggesting stimulation of anthocyanin biosynthesis. More DEGs were apparent at 1 day after ethephon treatment suggesting its early influence during ripening initiation. Overall, a higher number of genes were downregulated in response to ethylene. Many of these overlapped with cluster 1 genes, indicating that ethylene-mediated downregulation of photosynthesis is an important developmental event during the ripening transition. Analyses of DEGs in response to ethylene also indicated interplay among phytohormones. Ethylene positively regulated abscisic acid (ABA), negatively regulated jasmonates (JAs), and influenced auxin (IAA) metabolism and signaling genes. Phytohormone quantification supported these effects of ethylene, indicating coordination of blueberry fruit ripening by ethylene. Conclusion - This study provides insights into the role of ethylene in blueberry fruit ripening. Ethylene initiates blueberry ripening by downregulating photosynthesis-related genes. Also, ethylene regulates phytohormone-metabolism and signaling related genes, increases ABA, and decreases JA concentrations. Together, these results indicate that interplay among multiple phytohormones regulates the progression of ripening, and that ethylene is an important coordinator of such interactions during blueberry fruit ripening.

Authors: Takuya Uragami, Takatoshi Kiba, Mikiko Kojima, Yumiko Takebayashi, Yuzuru Tozawa, Yuki Hayashi, Toshinori Kinoshita and Hitoshi Sakakibara.

bioRxiv (2024)

Abstract: "The directional and sequential flow of cytokinin in plants is organized by a complex network of transporters. Genes involved in several aspects of cytokinin transport have been characterized, but a large part of the elaborate system remains elusive. In this study, we have identified ABCC4 as a cytokinin efflux transporter gene. Using a transient expression system in tobacco leaves, we screened Arabidopsis transporter genes and isolated ATP-BINDING CASSETTE TRANSPORTER C4 (ABCC4). Further validation through drug-induced expression in Arabidopsis and heterologous expression in budding yeast revealed that ABCC4 effluxes the active form of cytokinins. During the seedling stage, ABCC4 was highly expressed in roots, and its expression was up-regulated in response to cytokinin application. Loss-of-function mutants of ABCC4 displayed enhanced primary root elongation, similar to mutants impaired in cytokinin biosynthesis or signaling, which was suppressed by exogenous trans-zeatin treatment. In contrast, overexpression of the gene led to suppression of root elongation. These results suggest that ABCC4 plays a role in the efflux of active cytokinin, thereby contributing to root growth regulation. Our findings contribute to unraveling the many complexities of cytokinin flow and enhance our understanding of the regulatory mechanisms underlying root system development in plants."

Authors: Benjamin Hubert, Olivier Leprince and Julia Buitink.

Journal of Experimental Botany (2024)

Abstract: "To ensure their vital role in disseminating the species, dormant seeds have developed adaptive strategies to protect themselves against pathogens and predators. This is orchestrated through the synthesis of an array of constitutive defenses that are put in place in a developmentally regulated manner, which are the focus of this review. We summarize the defense activity and the nature of the molecules coming from the exudate of imbibing seeds that leak into its vicinity, also referred to as the spermosphere. As a second layer of protection, the dual role of the seed coat will be discussed; as a physical barrier and a multi-layered reservoir of defense compounds that are synthesized during seed development. Since imbibed dormant seeds can persist in the soil for extended times, we address the question if during this period, a constitutively regulated defense program is switched on to provide further protection, using the well-defined pathogenesis-related (PR) protein family. In addition, we review the hormonal and signaling pathways that might be involved in the interplay between dormancy and defense and point out questions that need further attention."