Enhanced tolerance to heat stress in transgenic tomato seeds and seedlings overexpressing a trehalose-6-phosphate synthase/phosphatase fusion gene

A fusion gene coding for trehalose-6-phosphate synthase/phosphatase (TPSP) derived from Escherichia coli was introduced into tomato plants (Solanum lycopersicum cv. Joyful) to generate overexpressing lines and enhance the level of trehalose in the seeds. Trehalose has been implicated in tolerance to abiotic stress in plants, so the response to heat stress of seeds from the transgenic lines and seeds from wild-type plants were compared. Wild-type heat-treated seeds had a germination rate of 17%, while four transgenic lines had germination rates over 50% following heat stress. In one heat-treated transgenic line, 100% of the seeds germinated, and therefore had a germination rate six times that of seeds from wild-type plants. Moreover, quantitative PCR revealed that the expression of diverse genes that respond to heat stress was enhanced in TPSP transgenic seeds compared to wild-type seeds 150min after the onset of heat stress. The enhanced germination rate and expression of these genes in the transgenic seeds were essentially mimicked in wild-type seeds treated with 1mM exogenous trehalose. Therefore, accumulated trehalose and associated metabolites may act as signaling molecules that enhance the expression of heat stress-responsive genes and confer heat-stress tolerance to seeds.