Genome-Wide Identification and Expression Pattern of the N-acetylserotonin deacetylase (ASDAC) Gene Family in Orchidaceae

Orchids are a kind of horticultural plant with highly ornamental and medical value. N-acetylserotonin deacetylase (ASDAC) is the only reverse enzyme of the melatonin biosynthesis pathway, and plays an important role in regulating the balance of melatonin. Melatonin as a multifunctional molecule, is typically involved in plant growth and development regulation, as well as abiotic stress tolerance. Here, we aimed at identifying ASDAC genes from the orchid genome to provide valuable information for further study of the role of melatonin in orchids. In this study, a total of 7 ASDAC genes were identified from the 7 orchid genome with one member in each species. The 7 orchid ASDACs have an HDAC functional domain, and cluster together with functionally confirmed OsHDAC10 and AtHDAC14, it shows that these members may have function of N-acetylserotonin deacetylase. Furthermore, based on the phylogenetic, motif, and gene structure analysis, the same clusters orchid ASDAC or ASDAC-like genes generally contained similar introns and motifs, suggesting the distribution pattern of exons/introns and motifs were strongly related to phylogeny on an evolutionary basis. Interestingly, homologous genes of OsHDAC10 and AtHDAC14 in Gastrodia elata have low homology and not cluster together with rice and A.thaliana ASDACs, showing that ASDAC gene family may lost in the holomycoheterotrophic orchids. The Ka/Ks ratios of ASDAC gene pairs from lower plant to higher plant were less than one, suggested that ASDAC genes have undergone purifying selection during the evolution process. Cis-acting element analysis results showed that the promoter regions of orchid ASDAC genes contained plant growth and development, phytohormone, and stress-responsive elements. Moreover, most orchid ASDACs were expressed in the roots, stems, leaves, flowers, and seeds. Combined cis-acting element and tissue expression analysis, indicating orchid ASDAC genes are involved in melatonin regulation of growth and development, as well as melatonin responding to various stresses in orchids. These findings of orchid ASDAC genes may provide valuable information for further study of the role of melatonin in orchids.