Genome-wide analysis R2R3-MYB transcription factors in Xanthoceras sorbifolium Bunge and functional analysis of XsMYB30 in drought and salt stresses tolerance

Xanthoceras sorbifolium Bunge, commonly called yellowhorn, is a unique woody oil plant and virescence forestation trees species with environmental stress tolerance in northern China. The R2R3-MYB transcription factor family plays a critical role in the response of plants to abiotic stress. Until now, genome-wide identification and characterization of yellowhorn R2R3-MYB genes has not been elucidated. In this study, 126 putative R2R3-MYB genes were found in the yellowhorn genome. The phylogenetic analysis showed yellowhorn R2R3-MYBs and Arabidopsis R2R3-MYBs were clustered into 33 subgroups, and 28 subgroups of them included members from 2 species, while 4 subgroups were specific to one species. A total of 9 and 34 gene pairs were found to have tandem duplication and segmental duplication events, the latter might have been the main contributor to the expansion of yellowhorn R2R3-MYB genes. Moreover, the promoter region of these gene contains multiple cis-acting regulatory elements involved in plant adversity and phytohormone responses. Subsequently, we cloned XsMYB30 gene and its expression was strongly upregulated by treatment with drought, salt, ABA, MeJA and SA. Silencing of XsMYB30 markedly weakened tolerance to both drought and salt stresses, probably because of more ROS production and MDA content but less antioxidative enzyme activities, proline and ABA are accumulated in the silenced plants. Furthermore, silencing of XsMYB30 decreased the expression levels of several stress-related genes involved in encoding the key enzymes in ROS-scavenging system, proline biosynthesis and ABA signaling pathway after stress treatments. Our findings provide important information for future research on the function and regulation mechanisms of yellowhorn R2R3-MYB transcription factors.