Pollination-Induced Transcriptome and Phylogenetic Analysis in Cymbidium tortisepalum (Orchidaceae)

Abstract

Orchids comprise a group of ecologically and evolutionarily significant plants, and the Orchidaceae is one of the most abundant angiosperm families. Yet little is understood about the genetic control of its flower development. Like many orchids, Cymbidium tortisepalum ovaries develop only following pollination. In this study, high-throughput RNA-seq technology was used to characterize the C. tortisepalum transcriptome and to identify differentially expressed genes during floral development. A total number of 45 165 976 reads were generated and assembled into 60 301 unigenes. 38 643 unigenes matched to proteins in the NCBI database. To compare the transcriptomes of pre-pollinated and post-pollinated gynostemia, an RNA-seq method was used. RNA-seq abundance analysis identified potentially all of the transcribed genes in this species’ gynostemium before and after pollination, including 488 943 in the pre-pollinated gynostemium transcriptome, and 88 829 transcripts in the post-pollinated gynostemium. Further comparison of the transcripts revealed that 7252 genes had either been up-regulated or down-regulated in post-pollinated compared with pre-pollinated gynostemium development. The preponderance of auxin and ethylene biosynthesis and signaling pathway factors in these transcriptomes suggested that the early pollination-induced ovary development involves these two hormones, as has been observed in other species. The C. tortisepalum gynostemium RNA-sequencing data were compared to transcriptome data of Oryza sativa and Arabidopsis thaliana, including pre-pollination and post-pollination stages and total 11 conserved orthologs related to protein kinase were found by phylogenetic analysis. Therefore, the sequence and expression data produced from this study provides the most comprehensive sequence resource available for C. tortisepalum study to date.