Expressed sequence tags from organ-specific cDNA libraries of tea (Camellia sinensis) and polymorphisms and transferability of EST-SSRs across Camellia species

Tea is one of the most popular beverages in the world and the tea plant, Camellia sinensis (L.) O. Kuntze, is an important crop in many countries. To increase the amount of genomic information available for C. sinensis, we constructed seven cDNA libraries from various organs and used these to generate expressed sequence tags (ESTs). A total of 17,458 ESTs were generated and assembled into 5,262 unigenes. About 50% of the unigenes were assigned annotations by Gene Ontology. Some were homologous to genes involved in important biological processes, such as nitrogen assimilation, aluminum response, and biosynthesis of caffeine and catechins. Digital northern analysis showed that 67 unigenes were expressed differentially among the seven organs. Simple sequence repeat (SSR) motif searches among the unigenes identified 1,835 unigenes (34.9%) harboring SSR motifs of more than six repeat units. A subset of 100 EST-SSR primer sets was tested for amplification and polymorphism in 16 tea accessions. Seventy-one primer sets successfully amplified EST-SSRs and 70 EST-SSR loci were polymorphic. Furthermore, these 70 EST-SSR markers were transferable to 14 other Camellia species. The ESTs and EST-SSR markers will enhance the study of important traits and the molecular genetics of tea plants and other Camellia species.