Molecular cloning of Oncidium lip-development related genes that are disturbed by high temperature

Oncidium Grower Ramsey is one of major cut flower species in Taiwan, and the flower production is all over the year. However, high temperature of summer and autumn results in the poor quality of cut flowers, by that not only the branching and floral number of inflorescence drop severely, but the length of inflorescence is shorter than that developed in cool seasons. Besides, high temperature might cause the floral lips smaller and slightly deformed. I focused my study in the cloning of floral development-related genes that are interfered by high temperature. Pot plants with developing inflorescences were cultivated in growth chambers setting at regular (28/23℃) or high temperature (35/30℃), and floral lips at various developmental stages were collected for RNA extraction. By using DDRT-PCR technique, 1323 gene fragments shown differential expression were collected and 324 of them were cloned and sequenced. After Blast alignment, ten clones possessing high homology with known genes related to cell wall metabolism and cell expansion were selected and used as probes to examine the gene expression pattern during floral development. The expression of six genes（OACS, OPHAN1, OV-ATPase, OKTN, OExp1 and OAuxRFP）in lip tissues increased along with the normal development of floral bud; and high temperature hampered their gene activities. The expression of other four genes（OASD, OCCR, OEGase and OGA2ox）which were selected from high temperature-treated lips was confirmed to be enhanced by high temperature. OGA2ox was predicted to encode GA-2-oxidase which is a well-known enzyme to regulate the level of biologically active GAs in plant tissues. Although the GA content in floral lips were not determined, exogenous GA application to floral buds grown at high temperature was conducted to test the effect of GA on lip development. The results suggested that GA should be involved in the regulation of lip expansion.