Genome-wide analysis of the R2R3-MYB family reveals potential regulators of lignin and tricin metabolism in the model grass Setaria viridis.

R2R3-MYBs constitute one of the largest families of plant transcription factors and several members are involved in the regulation of distinct branches of the phenylpropanoid pathway, acting as activators or repressors of the biosynthesis of a plethora of specialized metabolites. Although R2R3-MYBs have been extensively characterized as regulators of lignin deposition in distinct cellular contexts and species, still little is known about their roles in regulating specific aspects of grass lignification. Here, we report on the genome-wide characterization of the R2R3-MYB family in the model grass Setaria viridis and identification of members potentially involved in the regulation of lignin/tricin metabolism. A total of 132 genes encoding R2R3-MYBs were found in S. viridis, which clustered in 43 well-supported subgroups. Comprehensive in silico expression, co-expression, and RT-qPCR analyses allowed the identification of 4 candidate SvMYBs that showed (i) similar expression profiles to that observed for lignin biosynthetic genes in a set of different organs/conditions of S. viridis; (ii) similar expression patterns to that of lignin biosynthetic genes along the S. viridis elongating internode; (iii) co-expression with several phenylpropanoid- and lignin-related genes in public transcriptomic databases; (iv) high expression levels in the top of the S. viridis elongating internode, a tissue undergoing active lignification. Three of these SvMYBs activated the promoters of lignin and tricin biosynthetic genes in transactivation assays using tobacco protoplasts. Altogether, our results suggest that these three transcription factors control grass-specific aspects of lignin deposition and further studies might confirm their ability to control lignin deposition and tricin metabolism in S. viridis.