Mung bean (Vigna radiate (L.) Wilczek) is an important traditional food legume crop, with high economic and nutritional value. It is widely grown in China and other Asian countries. Despite its importance, genomic information is currently unavailable for this crop plant species or some of its close relatives in the Vigna genus. In this study, more than 103 million high quality cDNA sequence reads were obtained from mung bean using Illumina paired-end sequencing technology. The processed reads were assembled into 48,693 unigenes with an average length of 874 bp. Of these unigenes, 25,820 (53.0%) and 23,235 (47.7%) showed significant similarity to proteins in the NCBI non-redundant protein and nucleotide sequence databases, respectively. Furthermore, 19,242 (39.5%) could be classified into gene ontology categories, 18,316 (37.6%) into Swiss-Prot categories and 10,918 (22.4%) into KOG database categories (E-value < 1.0E-5). A total of 6,585 (8.3%) were mapped onto 244 pathways using the Kyoto Encyclopedia of Genes and Genome (KEGG) pathway database. Among the unigenes, 10,053 sequences contained a unique simple sequence repeat (SSR), and 2,303 sequences contained more than one SSR together in the same expressed sequence tag (EST). A total of 13,134 EST-SSRs were identified as potential molecular markers, with mono-nucleotide A/T repeats being the most abundant motif class and G/C repeats being rare. In this SSR analysis, we found five main repeat motifs: AG/CT (30.8%), GAA/TTC (12.6%), AAAT/ATTT (6.8%), AAAAT/ATTTT (6.2%) and AAAAAT/ATTTTT (1.9%). A total of 200 SSR loci were randomly selected for validation by PCR amplification as EST-SSR markers. Of these, 66 marker primer pairs produced reproducible amplicons that were polymorphic among 31 mung bean accessions selected from diverse geographical locations. The large number of SSR-containing sequences found in this study will be valuable for the construction of a high-resolution genetic linkage maps, association or comparative mapping and genetic analyses of various Vigna species.

The adzuki bean (Vigna angularis (Ohwi) Ohwi and Ohashi) is an important grain legume of Asia. It is cultivated mainly in China, Japan and Korea. Despite its importance, few genomic resources are available for molecular genetic research of adzuki bean. In this study, we developed EST-SSR markers for the adzuki bean through next-generation sequencing. More than 112 million high-quality cDNA sequence reads were obtained from adzuki bean using Illumina paired-end sequencing technology, and the sequences were de novo assembled into 65,950 unigenes. The average length of the unigenes was 1,213 bp. Among the unigenes, 14,547 sequences contained a unique simple sequence repeat (SSR) and 3,350 sequences contained more than one SSR. A total of 7,947 EST-SSRs were identified as potential molecular markers, with mono-nucleotide A/T repeats (99.0%) as the most abundant motif class, followed by AG/CT (68.4%), AAG/CTT (30.0%), AAAG/CTTT (26.2%), AAAAG/CTTTT (16.1%), and AACGGG/CCCGTT (6.0%). A total of 500 SSR markers were randomly selected for validation, of which 296 markers produced reproducible amplicons with 38 polymorphic markers among the 32 adzuki bean genotypes selected from diverse geographical locations across China. The large number of SSR-containing sequences and EST-SSR markers will be valuable for genetic analysis of the adzuki bean and related Vigna species.

Rice bean (Vigna umbellata (Thunb.) Ohwi & Ohashi) is a warm season annual legume mainly grown in East Asia. Only scarce genomic resources are currently available for this legume crop species and no simple sequence repeat (SSR) markers have been specifically developed for rice bean yet. In this study, approximately 26 million high quality cDNA sequence reads were obtained from rice bean using Illumina paired-end sequencing technology and assembled into 71,929 unigenes with an average length of 986 bp. Of these unigenes, 38,840 (33.2%) showed significant similarity to proteins in the NCBI non-redundant protein and nucleotide sequence databases. Furthermore, 30,170 (76.3%) could be classified into gene ontology categories, 25,451 (64.4%) into Swiss-Prot categories and 21,982 (55.6%) into KOG database categories (E-value < 1.0E-5). A total of 9,301 (23.5%) were mapped onto 118 pathways using the Kyoto Encyclopedia of Genes and Genome (KEGG) pathway database. A total of 3,011 genic SSRs were identified as potential molecular markers. AG/CT (30.3%), AAG/CTT (8.1%) and AGAA/TTCT (20.0%) are the three main repeat motifs. A total of 300 SSR loci were randomly selected for validation by using PCR amplification. Of these loci, 23 primer pairs were polymorphic among 32 rice bean accessions. A UPGMA dendrogram revealed three major clusters among 32 rice bean accessions. The large number of SSR-containing sequences and genic SSRs in this study will be valuable for the construction of high-resolution genetic linkage maps, association or comparative mapping and genetic analyses of various Vigna species.