A Chinese jujube (Ziziphus jujuba Mill.) fruit-expressed sequence tag (EST) library: Annotation and EST-SSR characterization

- Chinese jujube (Ziziphus jujuba Mill), native to China, is an economically important plant species of the Rhamnaceae family.
- A cDNA library was constructed from fruits of Z. jujuba Mill 'Dongzao', and a number of ESTs were added to facilitate functional genomics and other studies in Chinese jujube.
- An SSR marker set containing 119 markers was developed, and was shown to be transferable to related species.

Characterization of gene expression in plants is important to understanding their physiology and breeding programs. This can be approached by generating partial mRNA transcript sequences, known as expressed sequence tags (ESTs). ESTs are useful for gene discovery and to identify molecular markers, such as simple sequence repeats (SSRs). In this study, we constructed a cDNA library using the fruit of Chinese jujube Ziziphus jujuba 'Dongzao', and obtained 1942 high-quality sequences. ESTs were assembled into 965 unigenes, including 239 contigs and 726 singletons. BLAST searches confirmed that 782 (81.0%) unigenes had homology to previously identified plant genes, and the remainder may represent unique clones not previously explored. Sequences with annotations were further clustered with Gene Ontologies (GO). A total of 686 (71.1%) unigenes were functionally classified into one or more categories. Furthermore, we identified 334 simple sequence repeats (SSRs) in the unigenes. Of the 219 primer pairs, 119 amplified successfully in 'Dongzao', among which 66 randomly selected could amplify in sour jujube (Z. acidojujuba C.Y. Cheng et M.J. Liu (Z. spinosa Hu.)) and another four Chinese jujube cultivars. The newly characterized genes and gene-derived markers from our EST library will facilitate genome annotations, novel gene discovery, molecular breeding and comparative genomics in Chinese jujube and related species.