The SIFSR gene controls fruit shelf-life in tomato

Fruit ripening represents a process that changes flavor and appearance and also a process that dramatically increases fruit softening. Fruit softening and textural variations mainly result from disruptions to the cell walls of the fruit throughout ripening, but the exact mechanisms and specific modifications of the cell wall remain unclear. Plant-specific GRAS proteins play a critical role in development and growth. To date, few GRAS genes have been functionally categorized in tomato. The expression of a novel GRAS gene described in this study and designated as SIFSR (fruit shelf-life regulator) specifically increased during fruit ripening, but was significantly decreased in the tomato mutant rin (ripening inhibitor). RNAi repression of SIFSR resulted in reduced expression of multiple cell wall modification-related genes, decreased the activities of PG (polygalacturonase), TBG (tomato (beta-galactosidase), CEL (cellulase), and XYL (beta-D-xylosidase), and significantly prolonged fruit shelf-life. Furthermore, overexpression of SIFSR in mutant rin gave rise to up-regulated expression of multiple cell wall modification-related genes, such as PG, TBG4, CEL2, XYL1, PL, PE, MAN1, EXP1, and XTH5, and significantly shortened the fruit shelf-life. These findings reveal some of the genetic mechanisms underlying fruit cell wall metabolism and suggest that the SIFSR gene is another potential biotechnological target for the control of tomato fruit shelf-life.