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e identification of key genes of economical and biologi cal interests. Complementary to the 4μ8C whole genome sequences, Expressed Sequenced Tags present an alternative valuable resource for research and breeding as they provide the most comprehensive information regarding the dynamics of cucumber transcriptome. It has been reported that ESTs have played significant roles 4μ8C in accelerating gene discovery including gene family expansion, improving genome annotation, elucidating phylogenetic relationships, facilitating breeding programs for both plants and animals by pro viding SSR and SNP markers, and large scale expression analysis, In addition, ESTs are a robust method for rapid identification of transcripts involved in specific biological processes.
Currently there are more than 64 million ESTs in the NCBI public collection, dbEST database, However, only around 8,000 EST sequences are available for cucumber and approximately 150,000 for all the species in the Cucurbitaceae family, of which GSK525762 50,000 are in the dbEST database Neuroblastoma and 100,000 recently generated melon ESTs are available in the Cucur bit Genomics Database, as compared to more than 1. 5 and 2 million ESTs available for Arabidopsis and maize, respectively. Recent advances in next generation sequencing tech nologies allow us to generate large scale ESTs efficiently and cost effectively. In this study, we report the genera tion of more than 350,000 high quality cucumber ESTs from flower buds of two near isogenic lines, a gynoecious plant which bears only female flowers and a her maphroditic plant which bears bisexual flowers, using Roche 454 massive parallel pyrosequencing tech nology.
These ESTs, together with GSK525762 5,600 high quality cucumber EST and mRNA sequences available in public domains, were clustered and assembled into 81,401 uni genes, which were further aligned to cucumber genome predicted genes and annotated extensively in this study. We then performed comparative digital expression profil ing analysis to systematically characterize the differences of mRNA expression levels between the two flowers with different sex types, in an attempt to identify genes playing roles in cucumber sex determination. Furthermore, puta tive SNP and SSR markers were identified from these ESTs.
Results and discussion Cucumber EST sequence generation and assembly We performed a half 454 GS FLX run on each of the two flower bud samples which were 4μ8C collected from two near isogenic lines, a gynoecious line which bears only female flowers and a hermaphroditic line which bears only bisexual flow ers. We obtained a total of approximately 405,000 raw reads. After removing low quality regions, adaptors and all possible contaminations, we obtained a total of 353,941 high quality ESTs with an average length of 175 bp and a total length of 61. 9 Mb, among which 188,255 were from WI1983G and 165,686 from WI1983H, The length distribution of these high quality ESTs is shown in Figure 1A. Despite a significant number of ESTs were very short, more than 80% fell between 100 and 300 bp in length. The ESTs generated in this study, together with 5,196 high quality ESTs and 420 mRNA sequences available in GenBank, GSK525762 were subjected to cluster and assembly analy ses.
A total of 81,401 unigenes were obtained, among which 28,452 were contigs and 52,949 were singletons. The unigenes had an average length of 231. 5 bp and a total length of 4μ8C approximately 18. 8 Mb, The length distributions of singletons, contigs and unigenes, GSK525762 respectively, are shown in Figure 1B, revealing that more than 8,000 contigs are greater than 400 bp, while only around 400 singletons are greater than 400 bp. The distribution of the number of ESTs in cucumber unigenes is shown in Figure 2. From our EST collection, we were able to identify a number of highly abundant transcripts in cucumber flowers. Around 4,400 tran scripts have more than 10 EST members and these 4,400 transcripts contain 62% of the EST reads. Alternative Splicing in Cucumber Alternativ