Comparative transcript profiling explores differentially expressed genes associated with sexual phenotype in kiwifruit

Background
Kiwifruit is a perennial, deciduous and functionally dioecious plant. However, very little is known about the whole-genome molecular mechanisms contributing to distinct sexual phenotypes. To gain a global view of genes differentially expressed between male and female flowers, we analyzed genome-wide gene expression profiles in the flowers of male and female plants using high-throughput RNA sequencing.
Results
A total of 53.5 million reads were generated. Based on the alignments of unigenes to kiwifruit genome predicted genes, a total of 39,040 unique genes with a mean length of 970 bp were identified. There were 2,503 UniGenes differentially expressed between female and male flowers, with 1,793 up-regulated and 710 down-regulated in the female flowers. Moreover, the gene expression pattern of 17 out of 19 unigenes differentially expressed between male and female flowers revealed by RNA-Seq was confirmed by real-time quantitative PCR (qRT-PCR).
Conclusions
Here, we obtained a large number of EST sequences from female and male flowers of kiwifruit. This comparative transcriptome analysis provides an invaluable resource for gene expression, genomics, and functional genomic studies in A. chinensis and its related species. This study also represents a first step toward the investigation of genes involved in kiwifruit sex determination.

背景
猕猴桃为多年生落叶功能性雌雄异株植物。目前学界对调控其独特性别表型的全基因组分子机制仍鲜有研究。为全面解析雌雄花间差异表达基因的整体特征，本研究采用高通量RNA测序技术，对雌雄猕猴桃植株的花组织开展全基因组基因表达谱分析。
结果
本研究共获得5350万条测序读段。将单基因（unigene）与猕猴桃基因组预测基因进行序列比对后，共鉴定得到39040个独特基因，其平均长度为970 bp。雌雄花间共有2503个单基因呈现差异表达，其中雌花中有1793个基因上调表达，710个基因下调表达。此外，本研究通过实时定量聚合酶链式反应（real-time quantitative PCR, qRT-PCR），验证了RNA测序筛选出的19个雌雄差异表达单基因中17个的表达模式。
结论
本研究从猕猴桃雌雄花组织中获取了大量表达序列标签（expressed sequence tag, EST）。此项比较转录组分析为中华猕猴桃（Actinidia chinensis, A. chinensis）及其近缘物种的基因表达、基因组学及功能基因组学研究提供了宝贵的研究资源。本研究同时为解析猕猴桃性别决定相关基因的功能研究迈出了第一步。