Comprehensive analysis of ABA-aldehyde oxidase genes associated with drought and salt stress tolerance in wheat (Triticum aestivum L.).

ABA-aldehyde oxidase (AAO) acts as the final rate-limiting enzyme in ABA biosynthesis, and plays a critical role in plant growth and abiotic stress response. However, comprehensive analysis of AAO genes has not been reported in wheat. In this study, a total of 30 TaAAO genes were identified, and their physicochemical properties, evolutionary relationships, gene structures, cis-acting elements, expression patterns, upstream transcription factors, interacting proteins and drought-resistant superior haplotypes were systematically analyzed. Phylogenetic analysis showed that AAO proteins were divided into five subfamilies, and TaAAOs belonged to subfamilies A, B, C and E. All TaAAOs contained MoCo and FAD domains, and TaAAOs with closer evolutionary relationships exhibited the more similar composition of conserved motifs and exon-intron structures. Promoter analysis showed that ABRE, MeJA-responsive elements, MYC and STRE elements were the most enriched. qRT-PCR assay indicated that most TaAAO genes were significantly induced by drought and salt stresses. Especially, TaAAO2-A, TaAAO3-A, TaAAO4-A, TaAAO5-A, TaAAO7-A, TaAAO8-A and TaAAO10-A were significantly induced under both drought and salt stress. The upstream transcription factors and interacting proteins were also analyzed, and Y2H assay showed that TaAAO2-A could interact with Whirly transcription factor TaWHY1-7D. Haplotype analysis showed that TaAAO2-A-Hap II was the candidate drought-resistant haplotype with higher survival rate and expression level under drought stress. These results lay the foundation to study the function of TaAAO genes, and provide candidate genes for breeding stress-resistant wheat varieties.