Transcriptome analysis of Oncidium petals provides new insights into the initiation of petal senescence

The Oncidium Gower Ramsey orchid is both an important cut flower plant and a potential good model plant for study the ethylene-sensitive floral senescence. Though significant progress has been made in understanding the physiological and molecular events occurred in petal senescence, little is known regarding the regulatory mechanism underlying onset of petal senescence. In this study, RNA sequencing and transcriptome analysis of petals during the transition from Oncidium flower opening to senescence were employed to identify novel regulatory genes and pathways in the initiation of ethylene-sensitive petal senescence. The petal senescence is a very active process accompanying differential expressions of a large number of genes. The key genes involved in the biosynthesis of gibberellin (GA), brassinosteroid (BR) and salicylic acid (SA), cytokinin (CK) homeostasis, CK and jasmonate (JA) signalling were found to be down-regulated in opening stage but up-regulated in senescent stage, and a gene in ethylene signalling was the reverse, suggesting that these hormones might play a role in the start of petal senescence. The transition-pattern expressions of major circadian clock genes showed that the timing of petal senescence might be under the circadian clock regulation. Moreover, epigenetic and transcriptional regulations were involved in the onset of petal senescence.