VabHLH137 promotes proanthocyanidin and anthocyanin biosynthesis and enhances resistance to in grapevine.

Proanthocyanidins (PAs) and anthocyanins are involved in the response of plants to various environmental stresses. However, the mechanism behind defense-induced PA biosynthetic regulation is still not completely elucidated, also in grapevine. This study performed a transcriptome sequencing analysis of grape berries infected with to highlight the induction of the VabHLH137 factor from the basic helix-loop-helix (bHLH) XII subfamily by the fungus, which appeared to be significantly co-expressed with PA-related genes. The functional analysis of VabHLH137 overexpression and knockdown in transgenic grape calli showed that it positively regulated PA and anthocyanin biosynthesis. Moreover, VabHLH137 overexpression in the grape calli significantly increased resistance to A yeast one-hybrid and electrophoretic mobility shift assay revealed that VabHLH137 directly bound to the promoter, enhancing its activity and interacting with VaMYBPAR, a transcriptional activator of PA biosynthesis. Furthermore, transient experiments showed that although the VabHLH137 + VaMYBPAR complex activated expression, it failed to further enhance expression compared to VaMYBPAR alone. The findings indicated that VabHLH137 enhanced PA biosynthesis by activating of expression, providing new insight into the transcriptional regulation of defense-induced PA biosynthesis in grapevine.