Abstract
Gibberellins (GAs) regulate numerous developmental processes in grapevine (Vitis vinifera) such as rachis elongation, fruit set, and fruitlet abscission. The ability of GA to promote berry enlargement has led to its indispensable use in the sternospermocarpic ('seedless') table grape industry worldwide. However, apart from VvGAI1 (VvDELLA1), which regulates internode elongation and fruitfulness, but not berry size of seeded cultivars, little was known about GA signalling in grapevine. We have identified and characterized two additional DELLAs (VvDELLA2 and VvDELLA3), two GA receptors (VvGID1a and VvGID1b), and two GA-specific F-box proteins (VvSLY1a and VvSLY1b), in cv. Thompson seedless. With the exception of VvDELLA3-VvGID1b, all VvDELLAs interacted with the VvGID1s in a GA-dependent manner in yeast two-hybrid assays. Additionally, expression of these grape genes in corresponding Arabidopsis mutants confirmed their functions in planta. Spatiotemporal analysis of VvDELLAs showed that both VvDELLA1 and VvDELLA2 are abundant in most tissues, except in developing fruit where VvDELLA2 is uniquely expressed at high levels, suggesting a key role in fruit development. Our results further suggest that differential organ responses to exogenous GA depend on the levels of VvDELLA proteins and endogenous bioactive GAs. Understanding this interaction will allow better manipulation of GA signalling in grapevine.
Highlights
Bioactive gibberellins (GA) are phytohormones involved in major physiological processes (Fleet and Sun, 2005; Yamaguchi, 2008)
Spatiotemporal analysis of VvDELLAs showed that both VvDELLA1 and VvDELLA2 are abundant in most tissues, except in developing fruit where VvDELLA2 is uniquely expressed at high levels, suggesting a key role in fruit development
VvGID1a is located on chromosome 14, and its intron size is 900 bp meaning it is encoded by a 1935 bp sequence, while VvGID1b is located on chromosome 7, and is encoded by a 1817 bp sequence containing a 782 bp intron
Summary
Bioactive gibberellins (GA) are phytohormones involved in major physiological processes (Fleet and Sun, 2005; Yamaguchi, 2008). The most common bioactive GAs in higher plants are GA1, GA4, and GA7, a small subset of the more than 136 GAs identified (MacMillan, 2001). The richest sources of GAs in most plants are seeds (Dennis Jr. and Nitsch, 1966), inflorescences, and nodes (Kaufman et al., 1976). GA is synthesized in the embryo (Kaneko et al, 2003), while the tapetum of anthers, stamens, flower receptacles, and rosette leaves constitute specific synthesis sites in flowering plants (Kaneko et al, 2003; Hu et al, 2008). GA levels are elevated in reduced GA-response mutant backgrounds, and vice versa (Thomas et al, 1999; Ueguchi-Tanaka et al, 2005; Griffiths et al, 2006)
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