Transcriptional Profiling of Rapidly Growing Cucumber Fruit by 454-Pyrosequencing Analysis

Fruit development proceeds from cell division to expansion, maturation, and ripening. Expansion is critical for size, yield, and quality; however, this period of development has received little attention. We used 454-pyrosequencing to develop a cucumber (Cucumis sativus) fruit transcriptome, identify highly expressed transcripts, and characterize key functions during exponential fruit growth. The resulting 187,406 expressed sequence tags (ESTs) were assembled into 13,878 contigs. Quantitative real-time polymerase chain reaction (qRT-PCR) verification of differentially expressed genes from fruit of different ages, and high correlation in transcript frequency between replicates, indicated that number of reads/contig reflects transcript abundance. Putative homologs were identified in Arabidopsis thulium, for 89% of the contigs represented by at least 10 ESTs; another 4% had homologs in other species. The remainder had homologs only in cucurbit species. The most highly expressed contigs were strongly enriched for growth (aquaporins, vacuolar ATPase, phloem proteins, tubulins, actins, cell wall-associated, and hormone-related), lipid, latex, and defense-related homologs. These results provide a resource for gene expression analysis in cucumber, profile gene expression in rapidly growing fruit, and shed insight into an important, but poorly characterized, developmental stage influencing fruit yield and quality.