Zhaniya S Batyrshina
Reut Shavit
Beery Yaakov
Samuel Bocobza
Vered Tzin

Benzoxazinoids are specialized metabolites that are highly abundant in staple crops, such as maize and wheat. Although their biosynthesis has been studied for several decades, the regulatory mechanisms of the benzoxazinoid pathway remain unknown. Here, we report that the wheat transcription factor TaMYB31 functions as a regulator of benzoxazinoid biosynthesis genes. A transcriptomic analysis of the tetraploid wheat (Triticum turgidum) tissue revealed the upregulation of both TaMYB31 homoeologous genes upon aphid and caterpillar feeding. TaMYB31 gene silencing in the hexaploid wheat Triticum aestivum significantly reduced benzoxazinoid metabolite levels and led to the plants' susceptibility to herbivores. Thus, aphid progeny production, caterpillar body weight gain, and spider mite oviposition significantly increased in TaMYB31-silenced plants. A comprehensive transcriptomic analysis of hexaploid wheat revealed that the TaMYB31 gene is co-expressed with the target benzoxazinoid-encoded genes, Bx, under several biotic and environmental conditions. Thus, we analyzed the effect of abiotic stresses on benzoxazinoid levels and discovered a strong accumulation of these compounds in the leaves. The results of a dual fluorescence assay indicated that TaMYB31 binds to the Bx1 and Bx4 gene promoters, thereby activating the transcription of benzoxazinoid-involved genes. Our finding is the first report of the transcriptional regulation mechanism of the benzoxazinoid pathway.