DEVELOPING EXPRESSED SEQUENCED TAGS (ESTS) FOR WATERMELON FRUIT

Abstract

A cDNA library was assembled using mRNA of watermelon fruit. The cDNA library was normalized and subtracted by hybridization with leaf cDNA of the same watermelon cultivar (Illini Red). 1,046 cDNA clones were sequenced to identify genes associated with fruit development and quality. Of 1,046 cDNA clones sequenced, 832 were unique sequences and designated as expressed sequenced tags (ESTs). Of the 832 ESTs, 205 (24.6%) have not been reported in any other plant species. Additionally, 186 ESTs (22.4%) correspond to genes with unknown function, while 441 ESTs (53.0%) correspond to genes with known function in other plant species. These ESTs are mainly associated with primary metabolism, membrane transport, cytoskeleton synthesis and structure, cell wall and cell division, signal transduction, nucleic acid binding and transcription factors, and defense and stress response. Differential expression of the ESTs was examined using microarray analysis. About 200 (24%) of the 832 ESTs showed differential expression during the development and ripening of watermelon fruit. The ESTs were also screened for simple sequence repeat (SSR) motifs. Of 832 ESTs screened, 177 contain SSR motifs. Primer pairs are being designed for these ESTs, and will be used for development of EST-SSR markers and for mapping on a genetic linkage map constructed for watermelon. This study provides valuable information on genes controlling watermelon fruit development and quality.