Fruit-specific over-expression of human S-adenosylmethionine decarboxylase gene results in polyamine accumulation and affects diverse aspects of tomato fruit development and quality

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 (~50 %) production, ~10 days delay in on-vine ripening and extended post-harvest storage of ~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.