Genes impinging on tolerance to seasonal abiotic stresses in peach

Dormancy plays a crucial role in plant meristem survival during the cold period in temperate climates. Meristem growth cessation and specific mechanisms for stress tolerance operate during this period, alleviating the deleterious effect of low temperature and water deprivation. We have performed gene expression studies in buds undergoing dormancy release in order to identify putative factors and pathways involved in stress tolerance in dormant buds. We have identified PpSAP1 and PpeS6PDH genes coding respectively for a stress associated protein-like and a sorbitol-6-phosphate dehydrogenase enzyme, both of which are downregulated in dormancy released flower buds of peach. Overexpression of PpSAP1 in transgenic plums reduces water loss under desiccation conditions and impairs cell growth. Gene expression studies indicate PpSAP1 could modulate water loss and cell growth by an ubiquitin-dependent mechanism affecting transcriptional regulation of specific targets. On the other hand, PpeS6PDH is a key enzyme involved in sorbitol synthesis, as stated by biochemical assays of purified recombinant protein. PpeS6PDH shows higher expression in dormant buds, in concordance with sorbitol accumulation data. Sorbitol has been described as a compatible solute and cryoprotectant in different species, which suggests its participation in freezing and water stress tolerance mechanisms in dormant buds.