The effect of heat and salicylic acid on the DAHPS expression and activity in grape cells

High temperatures affect grape berry set and development, alter the normal sugar content of the fruit, and reduce the accumulation of anthocyanins. Also, peaks of high temperature may stop the ripening progress. Despite its impact in fruit and wine quality, the mechanisms contributing to the reduction of anthocyanin levels under high temperature are still elusive. Some studies indicate that this reduction is caused by a downregulation of the genes responsible for anthocyanin synthesis, while others propose that heat upregulates anthocyanin degradation. The enzyme 3-deoxy-D-arabino-heptulo-sonate 7-phosphate synthase (DAHPS), which as two isoforms in plants (DAHPS-01 cytosolic and Co2+ activated; DAHPS-02 plastidial and Mn2+ activated), catalyzes the first step of the Shikimate pathway by condensing phosphoenolpyruvate and D-erythrose 4-phosphate to form 3-deoxy-D-arabino-heptulo-sonate 7-phosphate. The final product of this pathway is phenylalanine that fuels the Flavonoid pathway responsible for the biosynthesis of anthocyanins and proanthocyanidins (condensed tannins). Despite its recognized importance, very little is known about the role of DAHPS in the synthesis and accumulation of important secondary metabolites under heat stress. In this study, we aim at the elucidation of the genetic and biochemical steps that regulate anthocyanin accumulation in grape cells under heat. Results on the effect of high temperature and salicylic acid (SA), a plant hormone involved in abiotic stress response, on the expression and biochemical activity of DAHPS in grape cell suspensions are presented and discussed.This work is supported by FCT (PTDC/AGR-ALI/100636/2008) Henrique Noronha is supported by FCT, grant ref. SFRH/BD/75257/201