Isolation and Characterization of Fruit-specific Promoters ACS4 and EXP1 from Tomato (Solanum lycopersicum L)

Promoter engineering in plants holds a great promise for understanding complexity of genetic regulatory system in response to specific internal and external cues and for crop improvement. In the present investigation, we report characterization of two fruit-specific promoters SlACS4 and SlEXP1 that were isolated from tomato (Solanum lycopersicum L cv Pusa Ruby). In silico analysis of the cloned promoter sequences revealed the presence of a seed-specific cis-element in SlACS4 and several putative seed, embryo and endosperm-specific cis-elements in SlEXP1 in addition to fruit-specific ethylene responsive regulatory elements. The fruit- and seed-specific expression of both the promoters was analyzed in transgenic tomato lines expressing the promoter::GUS fusion constructs. The SlACS4 promoter (−1 to -373) showed GUS activity restricted specifically to flower buds and seeds in fruits. On the contrary, the SlEXP1 promoter (−1 to -769) showed high level of expression in seeds as compared to fruit tissues at different stages of fruit ripening. No GUS expression was observed in leaves satisfying the fruit-specific nature of both the promoters. Based on deletion analysis, minimal promoters SlACS4DL2 (−1 to -126) and SlEXP1DL1 (−1 to -254) were identified which can be used to drive tissue-specific expression of transgenes for introducing traits of agronomic importance such as resistance to fruit borer and for enhancing both nutritional and keeping quality of tomato fruits.