Abstract
MYB proteins are involved in diverse important biological processes in plants. Herein, we obtained the MYB superfamily from the allotetraploid Brassica napus, which contains 227 MYB-related (BnMYBR/Bn1R-MYB), 429 R2R3-MYB (Bn2R-MYB), 22 R1R2R3-MYB (Bn3R-MYB), and two R1R2R2R1/2-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 the Bn2R-MYBs and BnMYBRs were highly conserved. The whole superfamily was unevenly distributed on 19 chromosomes and underwent unbalanced expansion in B. napus. Allopolyploidy between B. oleracea and B. rapa mainly contributed to the expansion in their descendent B. napus, in which B. 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 four Bn2R-MYBs under the control of the viral CaMV35S and/or native promoters could rescue the lesser root hair phenotype of the Arabidopsis thaliana wer mutant plants, proving the conserved negative roles of the 2R-MYBs of the S15 subfamily in root hair development. RNA-sequencing data revealed that the Bn2R-MYBs and BnMYBRs had diverse transcript profiles in roots in response to the treatments with various hormones. Our findings provide valuable information for further functional characterizations of B. napus MYB genes.
Highlights
MYB proteins are characterized by a conserved DNA-binding domain comprising 1–4 conserved MYB repeats (R1–R3) [1,2,3]
To ensure that no MYB proteins were eliminated by lack of correspondence to the consensus, a representative sequence from each subfamily of the MYB-related proteins (MYBRs), 2R-MYB, 3R-MYB, and 4R-MYB proteins [4,5,22] was used as a query in the BLASTP search with a low-stringency stringent criterion
A total of 680 non-redundant putative BnMYBs were identified in B. napus Darmor–bzh [24] including 227 BnMYBR (33.4%), 429 Bn2R-MYB (63.1%), 22 Bn3R-MYB (3.2% including 17 typical Bn3R-MYB and five Bn3R-MYB-like genes) and two Bn4R-MYB (0.3%) genes
Summary
MYB proteins are characterized by a conserved DNA-binding domain comprising 1–4 conserved MYB repeats (R1–R3) [1,2,3]. Given an evident boosting trend of new subfamilies in the 2R-MYB family, to gain further insights into the evolutionary mechanisms of this gene family, we conducted a phylogenetic analysis of all putative 2R-MYB genes identified in 16 species (including nine Brassicaceae and seven closely related non-Brassicaceae species). These data allowed us to provide a more detailed classification and assessment of the evolutionary patterns of differentiation and proliferation of the 2R-MYB family in higher plants. To identify the BnMYB genes, which act in the roots in a hormone-dependent manner, we analyzed the RNA-sequencing (RNA-seq) data of the roots of B. napus MYB plants exposed to various hormone treatments
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