Expressing the sweet potato orange gene in transgenic potato improves drought tolerance and marketable tuber production.

Potato (Solanum tuberosum L.) is generally considered to be sensitive to drought stress. Even short periods of water shortage can result in reduced tuber production and quality. We previously reported that transgenic potato plants expressing the sweet potato orange gene (IbOr) under the control of the stress-inducible SWPA2 promoter (referred to as SOR plants) showed increased tolerance to methyl viologen-mediated oxidative stress and high salinity, along with increased carotenoid contents. In this study, in an effort to improve the productivity and environmental stress tolerance of potato, we subjected transgenic potato plants expressing IbOr to water-deficient conditions in the greenhouse. The SOR plants exhibited increased tolerance to drought stress under greenhouse conditions. IbOr expression was associated with slightly negative phenotypes, including reduced tuber production. Controlling IbOr expression imparted the same degree of drought tolerance while ameliorating these negative phenotypic effects, leading to levels of tuber production similar to or better than those of wild-type plants under drought stress conditions. In particular, under drought stress, drought tolerance and the production of marketable tubers (over 80g) were improved in transgenic plants compared with non-transgenic plants. These results suggest that expressing the IbOr transgene can lead to significant gains in drought tolerance and tuber production in potato, thereby improving these agronomically important traits.

Development of molecular markers, based on chloroplast and ribosomal DNA regions, to discriminate three popular medicinal plant species, Cynanchum wilfordii, Cynanchum auriculatum, and Polygonum multiflorum.

Identification of plant species is important for standardizing herbal medicine. Cynanchum wilfordii (Baekshuoh in Korean) and Polygonum multiflorum (Hashuoh in Korean) are important oriental medicinal herbs in Korea, Japan, and China. Cynanchum auriculatum is a faster growing and more productive plant than C. wilfordii; and, it is not recognized as a medicinal plant in the Korean Pharmacopoeia. C. wilfordii, P. multiflorum, and C. auriculatum are often misidentified in the Korean herbal medicine marketplace due to their morphological similarities and similar names. In this study, we investigated molecular authentication of these three medicinal plants using DNA sequences in the TrnL-F chloroplast intergenic region. Specific species identification was achieved by detecting allelic variations of single nucleotide polymorphisms (SNPs) using amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and high resolution melting curve analysis. Our results demonstrate that the intraspecific genetic distance between C. wilfordii and C. auriculatum is relatively low. We also developed a quantitative PCR assay using species-specific TrnL-F primers, which allowed us to estimate the ratio of C. wilfordii and C. auriculatum using varying ratios of mixed genomic DNA template from the two species. Additionally, to identify species in hybrid plants produced by cross-fertilization, we analyzed nuclear ribosomal DNA internal transcribed spacer regions in C. wilfordii and C. auriculatum by ARMS-PCR. Our results indicate that SNP-based molecular markers, usable to barcode tools could provide efficient and rapid authentication of these closely related medicinal plant species, and will be useful for preventing the distribution of products contaminated with adulterants.

Overexpression of the sweet potato IbOr gene results in the increased accumulation of carotenoid and confers tolerance to environmental stresses in transgenic potato.

In a previous study, we have evidenced that the overexpression of the IbOr gene isolated from sweet potato conferred a tolerance activity against salinity and methyl viologen (MV) treatment in transgenic sweet potato calli along with an enhanced carotenoid content. In this study, to further examine the function of the IbOr gene in heterologous organism, we transformed the IbOr gene into potato under the direction of SWPA2 promoter, a strong inducible promoter upon treatment with various environmental stresses. Consistently with our previous study of sweet potato calli, the level of total carotenoid was elevated up to 2.7-fold (38.1 µg g(-1)DW) compared to the non-transgenic control, Atlantic cultivar. However, the composition of carotenoid was not influenced by the overexpression of the IbOr gene since only pre-existing carotenoids in the non-transgenic control including violaxanthin, lutien and ß-carotene were elevated at a similar level of total carotenoids. In general, the transcript levels for most of carotenogenesis-related genes were elevated in transgenic tuber, whereas they remained at similar levels in transgenic leaf tissues compared to those of non-transgenic controls. The increased levels of carotenoid content in the leaf or tuber tissue of transgenic lines were correlated with the enhanced tolerance activity against salt- or MV-mediated oxidative stresses and DPPH radical-scavenging activity. Our preliminary results suggest that further investigation is required for the development of a crop tolerant to salinity and other environmental stresses through the overexpression of the IbOr gene.