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

INTRODUCTION: 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. METHODS: 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. RESULTS: 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. CONCLUSION: These results lay the foundation to study the function of TaAAO genes, and provide candidate genes for breeding stress-resistant wheat varieties.