MYB Superfamily in Brassica napus : Evidence for Hormone-Mediated Expression Profiles, Large Expansion, and Functions in Root Hair Development.

MYB proteins are involved in diverse important biological processes in plants. Herein, we obtained theMYBsuperfamily from the allotetraploidBrassica napus, which contains 227MYB-related (BnMYBR/Bn1R-MYB), 429R2R3-MYB(Bn2R-MYB), 22R1R2R3-MYB(Bn3R-MYB), and twoR1R2R2R1/2-MYB(Bn4R-MYB) genes. Phylogenetic analysis classified the Bn2R-MYBs into 43 subfamilies, and the BnMYBRs into five subfamilies. Sequence characteristics and exon/intron structures within each subfamily of theBn2R-MYBs andBnMYBRs were highly conserved. The whole superfamily was unevenly distributed on 19 chromosomes and underwent unbalanced expansion inB. napus. Allopolyploidy betweenB. oleraceaandB. rapamainly contributed to the expansion in their descendentB. napus, in whichB. rapa-derived genes were more retained. Comparative phylogenetic analysis of 2R-MYB proteins from nine Brassicaceae and seven non-Brassicaceae species identified five Brassicaceae-specific subfamilies and five subfamilies that are lacking from the examined Brassicaceae species, which provided an example for the adaptive evolution of the 2R-MYB gene family alongside angiosperm diversification. Ectopic expression of fourBn2R-MYBs under the control of the viralCaMV35Sand/or native promoters could rescue the lesser root hair phenotype of theArabidopsis thaliana wermutant plants, proving the conserved negative roles of the2R-MYBs of the S15 subfamily in root hair development. RNA-sequencing data revealed that theBn2R-MYBs andBnMYBRs had diverse transcript profiles in roots in response to the treatments with various hormones. Our findings provide valuable information for further functional characterizations ofB. napusMYBgenes.