Benzoxazinoid biosynthesis helps young wheat plants to cope with both biotic and abiotic stresses

Wheat plants are continuously exposed to insect attack, which might lead even to total yield loss. Benzoxazinoids are specialized metabolites that play a broad range of roles, including: antifeedant, insecticidal, antimicrobial, and allelopathic activities. Although their biosynthesis has been studied for several decades, the regulatory mechanisms of the benzoxazinoid pathway remain unknown. In our research, we found that the transcription factor TaMYB31 functions as a regulator of benzoxazinoid-biosynthetic genes. Transcriptomic analysis of the tetraploid wheat Triticum turgidum 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. Moreover, TaMYB31-silenced plants were more susceptible to cereal aphids. We evaluated the interaction of TaMYB31 transcription factor and benzoxazinoid promoters in planta using a dual fluorescence assay. The assay results indicated that TaMYB31 binds to the Bx1 and Bx4 promoters, thereby activating the transcription of benzoxazinoid-involved genes. A comprehensive transcriptomic analysis of hexaploid wheat revealed that the TaMYB31 gene is co-expressed with the target benzoxazinoid-encoded genes under several biotic and environmental conditions. Therefore, we measured the effect of abiotic stresses on benzoxazinoid levels and detected a high accumulation of these compounds. Altogether, our finding is the first report on the transcriptional regulation mechanism of the benzoxazinoid pathway.