Genome-wide analysis of the R2R3-MYB transcription factor gene family expressed in Juglans regia under abiotic and biotic stresses

MYB transcription factors are important in plant stress response. However, the MYB genes of walnut (Juglans regia), an important oil crop, have yet to be analyzed comprehensively. Using bioinformatics methods, 226 walnut R2R3-MYB genes were discovered at the genome level in this study. The genes were classified into 23 subgroups based on their evolutionary relationships and were unequally distributed across 16 walnut chromosomes. The genes of the same subgroup exhibit similar but not identical gene structure and conserved motifs. The promoter region carries several cis-acting elements connected with plant stress response. Tandem and segmental duplications primarily contributed to R2R3-MYB gene amplification in walnut. A total of 232, 54 and 14 walnut R2R3-MYB genes were homologous to Populus trichocarpa, Arabidopsis thaliana, and Zea mays genes, respectively. The results of publicly available transcriptome sequencing and real-time quantitative PCR analysis revealed that the Juglans R2R3-MYB genes were induced to express after Colletotrichum gloeosporioides infection and various abiotic stress treatments. Results of co-expression studies indicated that walnut R2R3-MYB genes may be involved in the regulation of the ICE1-CBF pathway in cold signal transduction. Our findings offer new insight into the potential role of R2R3-MYB transcription factors in biotic and abiotic stresses and provide a theoretical groundwork for the molecular mechanisms underlying walnut adaptation to such stress.