Ascorbate oxidases in bread wheat: gene regulatory network, transcripts profiling, and interaction analyses provide insight into their role in plant development and stress response

Ascorbate oxidases (AAOs) are apoplastic enzymes of the multi-copper oxidase family and have a significant role in redox homeostasis. Herein, we identified 14 TaAAO genes consisting of two to five exons in the bread wheat genome. These genes are present on the A, B, and D subgenomes of chromosomes 5 and 7. Analyses of gene regulatory networks revealed the occurrence of growth and development, phytohormones, light, and stress-responsive cis-regulatory elements, which interact with a diverse range of transcription factors in the promoter region of these genes. Additionally, a few TaAAO genes showed miRNA-mediated regulation. The TaAAO proteins consisted of three conserved domains; Cu_oxidase1, Cu_oxidase2, and Cu_oxidase3, and clustered into two phylogenetic groups. The majority of TaAAOs showed higher expression in roots, and mostly upregulated at 6 h of salt stress. Further, a few genes also showed modulated expression in other vegetative and reproductive tissues, and in heat stress, drought stress and fungal infestations. The interaction of TaAAO proteins with antioxidant enzymes such as dehydroascorbate reductases, ascorbate peroxidases, monodehydroascorbate reductases, etc., and related molecules like ascorbic acid and dehydroascorbate exposed their synchronized functioning in redox homeostasis. These results revealed the varied functions of TaAAOs from development to the stress response. The current study will lay the groundwork to find out the detailed function of each gene in upcoming investigations.