Genome-wide analysis of R2R3-MYB transcription factors reveals their differential responses to drought stress and ABA treatment in desert poplar (Populus euphratica)

The R2R3-MYB transcription factors are widely involved in the regulation of plant growth, biotic and abiotic stress responses. Meanwhile, seed germination, which is stimulated by internal and external environments, is a critical stage in the plant life cycle. However, the identification, characterization, and expression profiling of the Populus euphratica R2R3-MYB family in drought response during seed germination have been unknown. Our study attempted to identify and characterize the R2R3-MYB genes in P. euphratica (PeR2R3-MYBs) and explore how R2R3-MYBs trigger the drought and abscisic acid (ABA) response mechanism in its seedlings. Based on the analysis of comparative genomics, 174 PeR2R3-MYBs were identified and expanded driven by whole genome duplication or segment duplication events. The analysis of Ka/Ks ratios showed that, in contrast to most PeR2R3-MYBs, the other PeR2R3-MYBs were subjected to positive selection in P. euphratica. Further, the expression data of PeR2R3-MYBs under drought stress and ABA treatment, together with available functional data for Arabidopsis thaliana MYB genes, supported the hypothesis that PeR2R3-MYBs involved in response to drought are dependent or independent on ABA signaling pathway during seed germination, especially PeR2R3-MYBs with MYB binding sites (MBS) cis-element and/or tandem duplication. This study is the first report on the genome-wide analysis of PeR2R3-MYBs, as well as the other two Salicaceae species. The duplication events and differential expressions of PeR2R3-MYBs play important roles in enhancing the adaptation to drought desert environment. Our results provide a reference for prospective functional studies of R2R3-MYBs of poplars and lay the foundation for new breeding strategies to improve the drought tolerance of P. euphratica.

Automated summary

This study aimed to identify, characterize, and analyze the expression profiles of R2R3-MYB genes in Populus euphratica (P. euphratica) during seed germination in response to drought stress and abscisic acid (ABA) treatment. Comparative genomics analysis identified 174 PeR2R3-MYB genes, many of which underwent whole genome duplication or segment duplication events. The expression data supported the hypothesis that PeR2R3-MYBs are involved in drought response through the ABA signaling pathway, especially those with MYB binding sites and/or tandem duplication. This study provides valuable insights for understanding the functions of R2R3-MYBs in P. euphratica and lays the foundation for breeding strategies to enhance drought tolerance.