El-Sharkawy Islam, Sherif Sherif, Abdulla Mahboob, Jayasankar Subramanian
Florida A&M University, Center of Viticulture and Small Fruit Research, Tallahassee, Florida, United States of America.
Faculty of Agriculture, Damanhour University, Damanhour, Egypt.
PLoS One. 2017 Jan 11;12(1):e0169440. doi: 10.1371/journal.pone.0169440. eCollection 2017.
Fruit growth depends on highly coordinated hormonal activities. The phytohormone gibberellin (GA) promotes growth by triggering degradation of the growth-repressing DELLA proteins; however, the extent to which such proteins contribute to GA-mediated fruit development remains to be clarified. Three new plum genes encoding DELLA proteins, PslGAI, PslRGL and PslRGA were isolated and functionally characterized. Analysis of expression profile during fruit development suggested that PslDELLA are transcriptionally regulated during flower and fruit ontogeny with potential positive regulation by GA and ethylene, depending on organ and developmental stage. PslGAI and PslRGL deduced proteins contain all domains present in typical DELLA proteins. However, PslRGA exhibited a degenerated DELLA domain and subsequently lacks in GID1-DELLA interaction property. PslDELLA-overexpression in WT Arabidopsis caused dramatic disruption in overall growth including root length, stem elongation, plant architecture, flower structure, fertility, and considerable retardation in development due to dramatic distortion in GA-metabolic pathway. GA treatment enhanced PslGAI/PslRGL interaction with PslGID1 receptors, causing protein destabilization and relief of growth-restraining effect. By contrast, PslRGA protein was not degraded by GA due to its inability to interact with PslGID1. Relative to other PslDELLA-mutants, PslRGA-plants displayed stronger constitutive repressive growth that was irreversible by GA application. The present results describe additional complexities in GA-signalling during plum fruit development, which may be particularly important to optimize successful reproductive growth.
果实生长依赖于高度协调的激素活动。植物激素赤霉素（GA）通过触发抑制生长的DELLA蛋白降解来促进生长；然而，这类蛋白对GA介导的果实发育的贡献程度仍有待阐明。分离并对三个编码DELLA蛋白的李属新基因PslGAI、PslRGL和PslRGA进行了功能表征。果实发育过程中的表达谱分析表明，PslDELLA在花和果实个体发育过程中受到转录调控，根据器官和发育阶段的不同，可能受到GA和乙烯的正向调控。PslGAI和PslRGL推导的蛋白质包含典型DELLA蛋白中存在的所有结构域。然而，PslRGA表现出一个退化的DELLA结构域，随后缺乏GID1-DELLA相互作用特性。在野生型拟南芥中过表达PslDELLA会导致整体生长出现显著破坏，包括根长、茎伸长、植株结构、花结构、育性，并且由于GA代谢途径的显著扭曲而导致发育严重迟缓。GA处理增强了PslGAI/PslRGL与PslGID1受体的相互作用，导致蛋白质不稳定并解除生长抑制作用。相比之下，PslRGA蛋白由于无法与PslGID1相互作用而不会被GA降解。相对于其他PslDELLA突变体，PslRGA植株表现出更强的组成型抑制生长，GA处理无法使其恢复。目前的结果描述了李属果实发育过程中GA信号传导的额外复杂性，这对于优化成功的生殖生长可能尤为重要。
