PpyGAST1 is potentially involved in bud dormancy release by integrating the GA biosynthesis and ABA signaling in ‘Suli’ pear (Pyrus pyrifolia White Pear Group)

Bud dormancy establishment is essential for perennial plants to survive cold winters, while dormancy release is important for the resumption of growth and flowering. Gibberellins (GAs) and abscisic acid (ABA) are involved in bud dormancy release, but the details of the regulatory pathway are still obscure. First, we measured the GAs contents in pear buds during dormancy transition. The content of GA1, one of the bioactive GAs, increased during dormancy release while GA4 was not detectable. Based on a ‘Suli’ pear (Pyrus pyrifolia White Pear Group) RNA sequencing analysis, we found that PpyGAST1, a GA-stimulated transcripts (GAST) gene family member, was rapidly up-regulated during dormancy release, with a concurrent up-regulation of PpyGA20OX2 and active GA level. Overexpression of PpyGAST1 in Arabidopsis resulted in earlier seed germination under mock-, ABA- and GA-treatment conditions, but there was no difference under paclobutrazol-treatment conditions, compared with the wild type. Additionally, the transgenic Arabidopsis lines showed higher AtGA20ox2, AtGA3ox1 and AtEXPA1 expression levels. We identified 17 GAST genes differentially expressed during dormancy transitions, with higher transcript abundancy levels during dormancy release. The expression levels of some GAST genes in the buds were regulated by both GA and ABA treatments during dormancy release. Together, these results indicate that GAST genes may be involved in the ABA- and GA-responsive pathway and their expressions are correlated with pear bud dormancy release. Our findings provide new insights into the possible molecular mechanisms integrating GA biosynthesis and ABA signaling during bud dormancy release.