An expressed sequence tag (EST) set from Citrus sinensis L.!Osbeck whole seedlings and the implications of further perennial source investigations

Compared with the large-scale single pass cDNA sequencing entries from annual plants, the NCBI database has very little sequence information from perennial plant species. Although similar to annuals in many biochemical pathways, perennials are unique in the fact that they posses long generation times. Without short cycle reproduction as an escape mechanism, perennials have evolved alternative survival mechanisms to pathogen attack and environmental stresses. The study of these alternate strategies by way of functional genomics will greatly increase the understanding of the biochemical changes underlining stress responses in perennials. Herein we analyze a set of expressed sequence tags (ESTs) produced from a 180-day-old whole immature sweet orange citrus seedling cDNA library. From this library, 7680 cDNAs were single pass sequenced from the 5' end, generating 6443 high quality ESTs. In the analysis, 2272 ESTs (35%) were found to significantly match (E-value less than or equal to 10(-10)) proteins with known function in the public databases using BLASTX. Additionally, 1457 ESTs (23%) significantly matched proteins with unknown function and 1619 ESTs (25%) matched to proteins described as putative. The remaining 1095 ESTs (17%) failed to match with significance to any protein sequence found in the public databases. ESTs matching to the photosynthetic proteins chlorophyll A/B binding protein, plastocyanin and ribulose-1,5-bisphosphate carboxylase were abundant, 6.0% of the total. Interestingly, stress related proteins such as low molecular weight heat shock proteins, peroxidases, lipid transfer proteins and metallothionein-like proteins were also abundant, 3.6% of the total, suggesting a role for these genes in citrus seedling development. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.