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Fruit development is orchestrated by a complex network of interactions between hormone signaling pathways. The phytohormone gibberellin (GA) is known to regulate a diverse range of developmental processes; however, the mechanisms of GA action in perennial fruit species are yet to be elucidated. In the current study, a GA signaling gene PslSLY1 , encoding a putative F-box protein that belongs to the SLY1 (SLEEPY1)/ GID2 (gibberellin-insensitive dwarf2) gene family, was isolated from Japanese plum (Prunus salicina). PslSLY1 transcript abundance declined as fruit development progressed, along with potential negative feedback regulation of PslSLY1 by GA. Subcellular localization and protein–protein interaction assays suggested that PslSLY1 functions as an active GA signaling component that interacts with the ASK1 (Arabidopsis SKP1) subunit of an SCF–ubiquitin ligase complex and with PslDELLA repressors, in a GA-independent manner. By using a domain omission strategy, we illustrated that the F-box and C-terminal domains of PslSLY1 are essential for its interactions with the downstream GA signaling components. PslSLY1 overexpression in wild-type and Arabidopsis sly1.10 mutant backgrounds resulted in a dramatic enhancement in overall plant growth, presumably due to triggered GA signaling. This includes germination characteristics, stem elongation, flower structure, and fertility. Overall, our findings shed new light on the GA strategy and signaling network in commercially important perennial crops. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ripening is a highly coordinated, irreversible event involving a series of physiological and biochemical changes, leading to the development of a soft fruit. One of the limiting factors that influence the economic value of fruit is the relatively short ripening period and limited shelf-life. In climacteric fruit, ethylene is a key regulator of ripening; however, recent research has shown that auxin also plays an important role during the event. To understand the contributions of ethylene, auxin and their interaction in ripening, two plum cultivars with widely varying fruit ripening behaviors were compared. The early cultivar, EG, exhibited a brief ripening process in association with rapid decline in firmness. The late cultivar, V9, displayed slow ripening behavior accompanying by notable extension in fruit firmness, resulting in prolonged shelf-life along with preserved fruit quality traits. Auxin has been suggested to play an indirect role in promoting fruit ripening via stimulating the transcription of several ethylene components, resulting in ethylene-induced fruit ripening and softening. This study shows further that there is a direct involvement of auxin in advancing ripening events independent of ethylene action through stimulating the transcription of several genes that encode cell-wall metabolism-related proteins critical for determining the fruit softening rate and potential shelf-life. These results support the hypothesis that the autonomous role played by auxin is as important as that of ethylene in determining not only fruit ripening behavior, but also in mediating other fruit quality traits including shelf-life. [ABSTRACT FROM AUTHOR]