Polyamines (PAs) have been implicated in fruit ripening where they antagonize the action of ethylene: a ripening inducing phytohormone. S-adenosylmethionine decarboxylase (SAMDC) is a key enzyme involved biosynthesis of higher PAs- spermidine and spermine. Here, we report the genetic modification of tomato fruit ripening and quality by over-expressing human-SAMDC driven by fruit-specific promoter (2A11). The PA analysis of ripening fruits from these transgenics showed elevated PA levels in comparison to wild-type (WT). The increased levels of higher PAs are correlated with the accumulation of heterologous SAMDC transcripts in such fruits. Transgenic fruits exhibited reduced levels of ethylene (similar to 50 %) production, similar to 10 days delay in on-vine ripening and extended post-harvest storage of similar to 11 days as compared to the WT fruits. As a result, these fruits showed improvement in various ripening traits like enhanced lycopene, vitamin C and total soluble solid. In Lesam fruits, an up-regulated expression of SlySAMDC, SlyEXP1, SlyTBG4, SlyDXS 1 and SlyPSY 1 was observed, while ethylene biosynthesis genes were down-regulated. Here, we have demonstrated the important role of PAs in altering the molecular and biochemical processes underlying fruit ripening by interfering with the ethylene biosynthesis.
