Cloning And Expression Analysis Of OnACO₂and OnERS1Gene From Oncidium Gower Ramsey

The Oncidium Gower Ramsey is a major orchid cut flower types with high ornamental value in the world. Flowers life is an important indicator of flower quality and an important horticultural character. The research on flower senescence of Oncidium orchid has important theoretical and practical significance. Ethylene plays an important regulatory role on many developmental processes such as cut flower and fruit senescence.1-aminocyclopropane-l-carboxylate (ACC) oxidase (ACO) is a rate-limiting enzyme in the biosynthesis of ethylene and ETR1receptor plays an important role in ethylene signal transduction. OnACO2gene (GeneBank accession number is KP410730) and OnERS1(GeneBank accession number is KP410729) was cloned from Oncidium Gower Ramsey using rapid amplification of cDNA ends (RACE) technology. The results of bioinformatics and expression analysis were as follows:1. OnACO2gene has a full-length cDNA of1376bp, presumably encoding a non-transmembrane protein of324amino acid, with a molecular weight of36413.5, an isoelectric point (IP) of5.71. The deduced OnACO2protein sequence contains DIOX_N and20G-Fe Ⅱ_Oxy domains and shares a sequence similarity of66%-91%with OnACO1and ACO proteins in other plant species. OnERS1is a gene encoded a trans-membrane protein of631amino acids with a molecular weight of70773.7, an isoelectric point (IP) of6.82. OnERS1shared a similarity of74%-99%among the ethylene receptor proteins of other plant species and belonged to the ETR1subfamily.2. The expression patterns of OnACO2gene were investigated by quantitative real-time PCR (qRT-PCR). Results showed that the relative expression was highest in gynandria, followed by sepals, lateral petals and leaves, lowest in roots, stems and lip petals. During the senescence of Oncidium cut flower, expression level of OnACO2in different parts of the flower increased dramatically, followed by the corresponding sharp increase in ethylene production. Gene expression analysis demonstrated that OnERSl gene had the highest expression levels in roots and gynandria, followed by those in sepals, lateral petals and leaves, lowest in stems and lip petals; during the cut flower senescence, the expression levels in various flower organs continually increased to a maximum at6d, and then declined sharply. At the same time, ethylene production increased slowly until8d, and then dramatically increased.The space-time specific expression of OnACO2and OnERSl gene in Oncidium senescence indicated that the cloned genes were a function gene for the flower senescence. As the OnACO2and OnERS1are important candidate genes for Oncidium flower anti-senescence improvement via molecule modification, the results will lay a foundation for gene engineering for Oncidium cut flower senescence.