Identification of SSRs and differentially expressed genes in two cultivars of celery (Apium graveolens L.) by deep transcriptome sequencing

Celery (Apium graveolens L.) is one of the most important and widely grown vegetables in the Apiaceae family. Due to the lack of comprehensive genomic resources, research on celery has mainly utilized physiological and biochemical approaches, rather than molecular biology, to study this crop. Transcriptome sequencing has become an efficient and economic technology for obtaining information on gene expression that can greatly facilitate molecular and genomic studies of species for which a sequenced genome is not available. In the present study, 15 893 516 and 19 818 161 high-quality sequences were obtained by RNA-seq from two celery varieties 'Ventura' and 'Jinnan Shiqin', respectively. The obtained reads were assembled into 39 584 and 41 740 unigenes with mean lengths of 683 bp and 690 bp, respectively. A total of 1939 simple sequence repeat (SSR) markers were identified in 'Ventura' and 2004 SSRs in 'Jinnan Shiqin'. Di-nucleotide repeats were the most common repeat motif, accounting for 55.49% and 54.84% in 'Ventura' and 'Jinnan Shiqin', respectively. A comparison of expressed genes between the two libraries, identified 338 differentially expressed genes (DEGs). Three hundred and three of the DEGs were annotated based on a sequence similarity search utilizing eight public databases. Additionally, the expression profile of eight annotated DEGs was characterized in response to abiotic stresses. The collective data generated in the present research represent a valuable resource for further genetic and molecular studies in celery.