Abstract
Transient increases in ethylene biosynthesis, achieved by tight regulation of transcription of specific ACC oxidase and ACC synthase genes, play a role in activation of grapevine bud dormancy release. The molecular mechanisms regulating dormancy release in grapevine buds are as yet unclear. It has been hypothesized that its core involves perturbation of respiration which induces an interplay between ethylene and ABA metabolism that removes repression and allows regrowth. Roles for hypoxia and ABA metabolism in this process have been previously supported. The potential involvement of ethylene biosynthesis in regulation of dormancy release, which has received little attention so far, is now explored. Our results indicate that (1) ethylene biosynthesis is induced by hydrogen cyanamide (HC) and azide (AZ), known artificial stimuli of dormancy release, (2) inhibitors of ethylene biosynthesis and signalling antagonize dormancy release by HC/AZ treatments, (3) ethylene application induces dormancy release, (4) there are two sets of bud-expressed ethylene biosynthesis genes which are differentially regulated, (5) only one set is transiently upregulated by HC/AZ and during the natural dormancy cycle, concomitant with changes in ethylene levels, and (6) levels of ACC oxidase transcripts and ethylene sharply decrease during natural dormancy release, whereas ACC accumulates. Given these results, we propose that transient increases in ethylene biosynthesis prior to dormancy release, achieved primarily by regulation of transcription of specific ACC oxidase genes, play a role in activation of dormancy release.
Highlights
Our previous efforts to understand the molecular mechanisms regulating dormancy release in grapevine buds resulted in a working model that outlines biochemical pathways potentially involved in artificially-induced bud dormancy release (Ophir et al 2009)
Our working model proposed that ethylene biosynthesis is triggered by artificial stimuli of grapevine bud break, and affects a cascade of biochemical events that leads to endodormancy release
Our current and previous results indicate that (1) ethylene biosynthesis is induced by HC and AZ, known stimuli of grapevine bud dormancy release, (2) biosynthesis and signaling of ethylene is essential for dormancy release, and (3) ethylene itself can serve as a stimulus of dormancy release (Fig. 1; Ophir et al 2009; Zheng et al 2015)
Summary
Our previous efforts to understand the molecular mechanisms regulating dormancy release in grapevine buds resulted in a working model that outlines biochemical pathways potentially involved in artificially-induced bud dormancy release (Ophir et al 2009). In this model, perturbation of mitochondrial cytochrome-pathway activity leads to respiratory stress resulting in an energy crisis. Our further results supported the predictive power of the model with respect to involvement of respiratory stress, hypoxia and ABA in bud endodormancy regulation (Ophir et al 2009; Vergara et al 2017; Zheng et al 2015). ACS and ACO genes occur as multigene families
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