Vigna is a genus of flowering plants in the legume family, and about 100 species belong to this genus, including azuki bean, blackgram and mungbean which are well-known in Asia. Among the species in Vigna genus, Vigna reflexo-pilosa has its own unique characteristic form as allotetraploid (2n=4x=44), whereas other Vigna species exist as a diploid form (2n=2x=22). In this study, we de novo assembled V. reflexo-pilosa genome and 22 accessions of 18 Vigna species’ transcriptome using NGS platform and calculated the Ks values of synteny blocks within V. reflexo-pilosa to determine the whole-genome duplication event existence. Two WGD events had occurred on V. reflexo-pilosa unlike V. radiata which only occurred once. Also, we tried to find out which progenitor had contributed to formation of V. reflexo-pilosa using transcriptome assemble results of 22 Vigna accessions. Ks value calculation between the transcriptome assemble results and predicted gene sets of V. reflexo-pilosa has been excuted. V. trinervia showed 2 peaks (0.0075, 0.0495) on its Ks value bin distribution and confirmed as A-type genome donor. Based on the peak value, we considered the predicted genes of V. reflexo-pilosa in Ks value range from 0.033 to 0.072 as B-type genes, inherited from other progenitor. Re-calculating the Ks values of 4,796 predicted genes in B-type with the transcriptome assemble results of 22 Vigna accessions, we were able to find 6 Vigna species, V. umbelleta(CIAT34386), V. umbelleta(2004T2), V. nakashimae, V. nepalensis, V. riukiuensis, V. minima as candidate B-type genome donor.

Mungbean (Vigna radiata) is a fast-growing, warm-season legume crop that is primarily cultivated in developing countries of Asia. We constructed a draft genome sequence of mungbean to facilitate genome research into the subgenus Ceratotropis and to enable a better understanding of the evolution of leguminous species. The draft genome sequence covers 80% of the estimated genome, of which 50.1% consists of repetitive sequences. In total, 22,427 high confidence protein-coding genes were predicted. Based on the de novo assembly of additional wild mungbean species, the divergence of what was eventually domesticated and the sampled wild mungbean species appears to have predated domestication. Moreover, the de novo assembly of a tetraploid Vigna species (Vigna reflexo-pilosa var. glabra) provided genomic evidence of a recent allopolyploid event. To further study speciation, we compared de novo RNA-seq assemblies of 22 accessions of 18 Vigna species and protein sets of Glycine max and Cajanus cajan. The species tree was constructed by a Bayesian Markov chain Monte Carlo method using highly confident orthologs shared by all 24 accessions. The present assembly of V. radiata var. radiata will facilitate genome research and accelerate molecular breeding of the subgenus Ceratotropis.