Background:Dioscorea opposita Thunb. is one of the top 10 most important edible tuber and root plants worldwide, have been widely cultivated for nutritional and medicinal purposes. Yam is susceptible to various biological and abiotic stresses that will affect the yield and quality of the tubers. The WRKY gene family are widely distributed in plants growth and respond to abiotic stresses. However, current information on WRKY characteristics in yam is limited. Results: This study identifed 22 DoWRKYgenes from transcriptome of Dioscorea spp., which were divided into 6 clades based on phylogenetic analysis. Analysis of conserved motifs showed that there were 10 conserved motifs, with lengths ranging between 17 and 50 amino acids. Expression pattern analysis showed DoWRKYgenes are expressed in different growth and development stages and responsed to a variety of abiotic stress. DoWRKY71 was up-regulated in the late stage of tuber expansion, and it was differentially expressed in cold and ABA stress. Therefore, further study indicated that DoWRKY71 protein was localized in the nucleus. Overexpression of DoWRKY71 enhanced the cold tolerance of transgenic tobacco, promoted abscisic acid-mediated stomatal closure. Conclusions: This paper is the first systematic analysis the WRKY gene family in Dioscorea spp., and provide a new insight for further studying WRKY transcription factors in Dioscorea spp.. The functional study of DoWRKY71 laid a theoretical foundation for further exploring the regulatory function of DoWRKY71 gene in the growth and development related signaling pathway of yam.

Yam (Dioscorea opposita) is a kind of vegetables with important nutritional, medicinal and economic value. To reveal the relationship between starch synthesis and gene expression in yam tubers at gene transcription level, transcriptome profiling was conducted by RNA-Seq in Bikeqi yam (Dioscorea opposita Thunb.) tubers at five key developmental stages (105, 120, 135, 150, and 165 days after sowing, DAS). Based on transcriptome sequencing data, a total of 45,867 unigenes were obtained. The results showed that 135 days after sowing are the key period of starch accumulation. During yam tuber development, 1,941 candidate differentially expressed genes (DEGs) were successfully classified into three GO categories, respectively, and there were 292, 267 and 478 unigenes in cellular component, molecular function and biological process. There were 767, 90 and 73 DEGs enriched in metabolic, plant hormone signal transduction and Plant-pathogen interaction pathway by Kyoto Encyclopedia of Genes and Genomes (KEGG), individually. Especially 72 DEGs were enriched in starch and sucrose metabolism pathway. In this pathway, the metabolic process was mainly positive regulated by genes encoding sucrose synthase, glucose-1-phosphate adenylyltransferase, alpha-trehalase, and so on. There was negative regulated by genes encoding beta-glucosidase. 10 DEGs involved in starch synthesis were selected to prove the accuracy of the RNA-Seq data by qPCR, 85% (34/40) of the results were consistent. The results lay a theoretical foundation be used for further understanding the starch synthesis mechanism of yam tubers development and accelerating breeding progress.

β-amylase (BAM) plays an important role in plant development and response to abiotic stresses. In this study, 5 DoBAM members were identified in yam (Dioscorea opposita Thunb.). A novel β-amylase gene BAM1, (named DoBAM1), was isolated from yam varieties Bikeqi and Dahechangyu. The open reading frame (ORF) of DoBAM1 is 2806 bp and encodes 543 amino acids. Subcellular localization analysis indicates that DoBAM1 localizes to the cell membrane and cytoplasm. In the yam variety Dahechangyu, the starch content, β-amylase activity, and expression of DoBAM1 were characterized and found to all be higher than in Bikeqi. DoBAM1 overexpression in tobacco is shown to promote the accumulation of soluble sugar and chlorophyll content and to increase the activities of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and β-amylase. Under cold treatment, we observed the induced upregulation of DoBAM1 and lower starch content and malondialdehyde (MDA) accumulation than in WT plants. In conclusion, these results demonstrate that DoBAM1 overexpression plays an advanced role in cold tolerance, at least in part by raising the levels of soluble sugars that are capable of acting as osmolytes or antioxidants.