Overexpression of tomato SlbHLH22 transcription factor gene enhances fruit sensitivity to exogenous phytohormones and shortens fruit shelf-life

Abstract

The basic helix-loop-helix (bHLH) proteins comprise the second largest superfamily of transcription factor that mediate various biochemical, physiological, and developmental processes in plants. The biological roles of these TFs are unknown, particularly in tomato. In this study, we isolated the tomato SlbHLH22 expressing significantly in fruits at early and later stages of development. The SlbHLH22 was overexpressed under control of CaMV 35S promoter. The transgenic tomato fruits exhibited sensitivity to exogenous phytohormone, such as ABA and IAA and ripened fast than WT fruits. However, the fruits remain insensitive to GA. It was observed that the transcript abundance of ABA and IAA related genes were also significantly upregulated in fruits overexpressing SlbHLH22. Compared to WT, the activities of peroxidase, superoxide dismutase, and catalase was lower in the transgenic fruits, while the MDA concentration was higher than in WT fruits. Similarly, the induced expressions of cell wall metabolism related genes (SlEXP1, SlLoxA, SlMAN, SlPE, and SlXTH5) were also observed in transgenic fruits. These results demonstrate that tomato SlbHLH22 expressions were regulated by phytohormones and identification of SlbHLH22 roles in post-harvest helps limit losses during handling, storage, and transportation.