Generation and analysis of expressed sequence tags from poplar (Populus alba × P. tremula var. glandulosa) suspension cells

We have analyzed 8962 expressed sequence tags (ESTs) obtained from poplar cell suspension culture to gain an insight into the changes in gene expression during their growth phase in suspension culture. Single pass sequencing from 5′-end of 8962 randomly selected cDNA clones resulted in 7586 high quality ESTs with average reading length of 517 bp. A total of 3378 unigenes, consisting of 1337 contigs and 2041 singletons, were formed after assembly using CAP3 program. Among them, 2091 unigenes (61.9%) were found to significantly match (BLASTX score more than 80) the proteins with known function and 949 (28.1%) matched significantly with those having unknown function in the public databases. The remaining 338 unigenes (10.0%) failed to show significant homology to any proteins in the public databases, suggesting that they represent novel sequences. A significant portion of highly expressed genes in poplar cells encodes cell wall-related proteins, such as extensin, polygalacturonase inhibiting protein and proline-rich protein. The potentiality of the ESTs resource in studying of the regulation of cell growth was proved by growth phase-dependent expression of several selected genes.