Heterologous Expression of BoPAP1 in Tomato Induces Stamen Specific Anthocyanin Accumulation and Enhances Tolerance to a Long-Term Low Temperature Stress

Abstract

Anthocyanins are ubiquitous plant secondary products that possess nutritive values and serve essential functions in plant defense. The purple kale (Brassica oleracea var. acephala f. tricolor) BoPAP1 gene, which encodes a MYB transcription factor associated with anthocyanin biosynthesis, was introduced into tomato (Solanum lycopersicum) under the control of the CaMV 35S promoter. Transgenic tomato plants exhibited restricted accumulation of anthocyanins in stamens under normal growth conditions. qPCR analysis revealed that the expression of the anthocyanin biosynthetic genes such as SlF3′5′H, SlDFR, and SlANS, as well as a bHLH gene SlTT8, was specifically induced in transgenic stamens. A yeast two-hybrid assay revealed that BoPAP1 was a transcription activator and could interact with SlTT8. Despite the absence of anthocyanins in seedlings under normal conditions, overexpression of BoPAP1 led to high levels of anthocyanins and chlorophylls in the transgenic seedlings that were exposed to low temperature for 2 weeks, which conferred chilling tolerance on transgenic tomato plants. The consistency of SlTT8 expression and anthocyanin accumulation was observed in both purple stamens and low temperature treated seedlings in transgenic lines. These results suggest that the endogenous bHLH gene SlTT8 could be a candidate bHLH gene involved in the tomato anthocyanin pathway. Considering that the inducible type of anthocyanins apparently does not interfere with the normal growth of the plant; it provides an optimized transgenic strategy for crop improvement.