The TaMYB44-TaMYB1 module regulates grain amylose biosynthesis and flour viscosity in wheat

Starch content and composition in wheat endosperm are the important factors determining wheat yield and quality. The amylose content is one of the key parameters to characterize the starch viscosity in wheat flour, which affects pasting time and peak viscosity (PV), and then affects the eating quality of flour-based food. However, the transcriptional regulatory mechanisms of amylose biosynthesis in wheat remain poorly understood. Here, we identified a MYB transcription factor, TaMYB44-4D that can bind to the TaWx-7A promoter through yeast one-hybrid screening. EMSA, Y1H and Transactivation assays demonstrated that TaMYB44-4D could bind to the TaWx-7A promoters and repress their transcription activity. Knock-out TaMYB44-A/B/D simultaneously increased the amylose content, total starch content, swelling power, and RVA parameters, whereas overexpression of TaMYB44-4D decreased these parameters. These results indicated that TaMYB44 functions as a transcriptional repressor of starch biosynthesis. We confirmed that TaMYB44 interacted with TaMYB1, and the similar phenotypes were observed in both the tamyb44-KO and tamyb1-KO lines, as well as in the TaMYB44-4D-OE and TaMYB1-6B-OE lines, suggesting that they acted as co-repressors. Finally, a single nucleotide polymorphism (SNP) T/C was found in the promoter of TaMYB44-D in different wheat varieties and had been confirmed to be associated with the expression levels of TaMYB44. Association analysis of phenotype and genotype in a wheat natural population revealed that varieties with the CC haplotype exhibited higher amylose content than those with the TT haplotype. In conclusion, our findings are of great significance for understanding the transcriptional regulation mechanism of wheat amylose synthesis and genetic improvement of wheat starch quality.