Transcriptome profile analysis of floral sex determination in cucumber

Cucumber has been widely studied as a model for floral sex determination. In this investigation, we performed genome-wide transcriptional profiling of apical tissue of a gynoecious mutant (Csg-G) and the monoecious wild-type (Csg-M) of cucumber in an attempt to isolate genes involved in sex determination, using the Solexa technology. The profiling analysis revealed numerous changes in gene expression attributable to the mutation, which resulted in the down-regulation of 600 genes and the up-regulation of 143 genes. The Solexa data were confirmed by reverse transcription polymerase chain reaction (RT-PCR) and real-time quantitative RT-PCR (qRT-PCR). Gene ontology (GO) analysis revealed that the differentially expressed genes were mainly involved in biogenesis, transport and organization of cellular component, macromolecular and cellular biosynthesis, localization, establishment of localization, translation and other processes. Furthermore, the expression of some of these genes depended upon the tissue and the developmental stage of the flowers of gynoecious mutant. The results of this study suggest two important concepts, which govern sex determination in cucumber. First, the differential expression of genes involved in plant hormone signaling pathways, such as ACS, Asr1, CsIAA2, CS-AUX1 and TLP, indicate that phytohormones and their crosstalk might play a critical role in the sex determination. Second, the regulation of some transcription factors, including EREBP-9, may also be involved in this developmental process.