Characterizing the transcriptome and microsatellite markers for almond (Amygdalus communis L.) using the Illumina sequencing platform

BACKGROUND The almond tree (Prunus amygdalus Batsch) is an important nut tree grown in subtropical regions that produces nutrient-rich nuts. However, a paucity of genomic information and DNA markers has restricted the development of modern breeding technologies for almond trees. RESULTS In this study, almonds were sequenced with Illumina paired-end sequencing technology to obtain transcriptome data and develop simple sequence repeats (SSR) markers. We generated approximately 64 million clean reads from the various tissues of mixed almonds, and a total of 42,135 unigenes with an average length of 988 bp were obtained in the present study. A total of 27,586 unigenes (57.7% of all unigenes generated) were annotated using several databases. A total of 112,812 unigenes were annotated with the Gene Ontology (GO) database and assigned to 82 functional sub-groups, and 29,075 unigenes were assigned to the KOG database and classified into 25 function classifications. There were 9470 unigenes assigned to 129 Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways from five categories in the KEGG pathway database. We further identified 8641 SSR markers from 48,012 unigenes. A total of 100 SSR markers were randomly selected to validate quality, and 82 markers could amplify the specific products of A. communis L., whereas 70 markers were successfully transferable to five species (A. ledebouriana, A. mongolica, A. pedunculata, A. tangutica, and A. triloba). CONCLUSIONS Our study was the first to produce public transcriptome data from almonds. The development of SSR markers will promote genetics research and breeding programmes for almonds.