Transcriptome analysis of female and male flower buds of Idesia polycarpa Maxim. var. vestita   Diels

Background: Idesia polycarpa Maxim. var. vestita Diels, a dioecious plant, is widely used for biodiesel due to the high oil content of its fruits. However, it is hard to distinguish its sex in the seedling stage, which makes breeding and production problematic as only the female tree can produce fruits, and the mechanisms underlying sex determination and differentiation remain unknown due to the lack of available genomic and transcriptomic information. To begin addressing this issue, we performed the transcriptome analysis of its female and male flower.
Results: 28,668,977 and 22,227,992 clean reads were obtained from the female and male cDNA libraries, respectively. After quality checks and de novo assembly, a total of 84,213 unigenes with an average length of 1179 bp were generated and 65,972 unigenes (78.34%) could be matched in at least one of the NR, NT, Swiss-Prot, COG, KEGG and GO databases. Functional annotation of the unigenes uncovered diverse biological functions and processes, including reproduction and developmental process, which may play roles in sex determination and differentiation. The Kyoto Encyclopedia of Genes and Genomes pathway analysis showed many unigenes annotated as metabolic pathways, biosynthesis of secondary metabolites pathways, plant–pathogen interaction, and plant hormone signal transduction. Moreover, 29,953 simple sequence repeats were identified using the microsatellite software.
Conclusion: This work provides the first detailed transcriptome analysis of female and male flower of I. polycarpa and lays foundations for future studies on the molecular mechanisms underlying flower bud development of I. polycarpa.

Keywords
Dioecious; Floral homeotic genes; Flower development; Functional annotation; Next generation sequencing technology; RNA sequencing (RNA-seq); Sex determination; Sex differentiation; Simple sequence repeats (SSR); Transcription factors; Transcriptome profiling