The TSJT1 protein belongs to the class-II glutamine amidotransferase (GATase) superfamily. Research on the functions and underlying mechanisms of TSJT1 in plants is limited. In this study, the abscisic acid (ABA)-inducible gene IbTSJT1 was isolated from drought-tolerant sweetpotato line Xushu 55-2. Its expression was strongly induced by PEG6000 and ABA. The IbTSJT1 protein was localized in the nucleus and cell membrane. IbTSJT1-overexpressing sweetpotato plants exhibited significantly enhanced drought tolerance. Their ABA and proline contents and superoxide dismutase (SOD) and peroxidase (POD) activities were increased, and their reactive oxygen species (ROS) scavenging-related genes were upregulated under drought stress. The stomatal aperture assay confirmed that the IbTSJT1-overexpressing plants had greater sensitivity to ABA. The results of yeast one-hybrid (Y1H) assay, electrophoretic mobility shift assay (EMSA), luciferase reporter assay and ChIP-qPCR assay indicated that IbABF2 can directly bind to the cis-acting ABA-responsive element (ABRE) in the IbTSJT1 promoter to activate the expression of IbTSJT1. These findings suggest that IbTSJT1 mediates ABA-dependent drought stress responses and enhances drought tolerance by inducing stomatal closure and activating the ROS scavenging system in transgenic sweetpotato. Our study provides a novel gene for improving drought tolerance in sweetpotato and other plants.

A glutathione S-transferase (GST) gene IbGSTL2 was cloned and characterized from sweetpotato. It harbored a variation associated with starch content in storage roots. Overexpression of IbGSTL2 increased starch content and amylopectin proportion, decreased gelatinization temperature, and improved degree of crystallinity in sweetpotato storage roots, while its RNA interference resulted in the opposite trends. IbGSTL2 physically interacted with IbcPGM, an enzyme of sucrose metabolism, and improve starch content and quality by regulating genes involved in starch biosynthesis.

Sweetpotato (Ipomoea batatas (L.) Lam.) is a widely grown food crop especially in developing countries. Increasing storage-root yield and dry-matter content has been the main breeding objective of the crop, and DNA marker-assisted breeding is needed for this purpose. In this study, using a mapping population of 500 F₁ individuals from a cross between Xushu 18 (female) and Xu 781 (male), we constructed a high-density genetic linkage map of sweetpotato using 601 simple-sequence repeat (SSR) primer pairs. The Xushu 18 map contained 90 linkage groups with 5547 SSR markers and spanned 18,263.5 cM, and the Xu 781 map contained 90 linkage groups with 4599 SSR markers and spanned 18,043.7 cM, representing the highest genome coverage yet reported for sweetpotato. We identified 33 QTL for storage-root yield and 16 QTL for dry-matter content, explaining respectively 6.5%–47.5% and 3.2%–18.9% of variation. These results provide a foundation for fine-mapping and cloning of QTL and for marker-assisted breeding in sweetpotato.

Simple sequence repeat (SSR) markers have been proved to be a very powerful tool for quantitative trait locus (QTL) mapping, marker-assisted selection and comparative genomics research in many crop species. However, a high-density SSR genetic linkage map is still lacking because there are only a few SSR markers available in sweet potato. In this study, a total of 2545 simple sequence repeat (SSR) primer pairs, including 1215 genomic SSR (gSSR) primer pairs and 1330 BES-SSR (bSSR) primer pairs designed from the genome sequence and BAC-end sequence of sweet potato, respectively, were screened with sweet potato cultivars Luoxushu 8 and Zhengshu 20 and their randomly sampled two F₁ individuals and 571 of them generated polymorphic bands. The selected 571 polymorphic SSR primer pairs and 35 EST-based SSR (eSSR) primer pairs developed at our laboratory were used to genotype 240 F₁ individuals derived from a cross between Luoxushu 8 and Zhengshu 20. A double pseudo-test-cross strategy was applied for linkage analysis. The Luoxushu 8 map included 90 linkage groups with 5057 SSR markers and covered 13,299.9 cM with a marker density of 2.6 cM, and the Zhengshu 20 map contained 90 linkage groups with 3009 SSR markers and covered 11,122.9 cM with a marker density of 3.7 cM. Fifteen homologous groups were identified in both parent maps. These are the first SSR linkage maps consisting of the complete 90 linkage groups and 15 homologous groups, which are consistent with the autohexaploid nature of sweetpotato, and are also the linkage maps with the highest SSR marker density reported to date. These results provide a basis for QTL mapping, marker-assisted breeding and comparative genomics research of sweet potato.

Sucrose non-fermenting-1-related protein kinase-1 (SnRK1) regulates carbon and nitrogen metabolism in plants. However, its roles and their underlying mechanisms in tolerance to abiotic stresses are little known. The present study indicated that the IbSnRK1 gene was strongly induced by NaCl, polyethylene glycol (PEG) 6000, hydrogen peroxide (H₂O₂), cold (4 ℃), and abscisic acid (ABA). Its overexpression significantly increased salt, drought, and cold tolerance in transgenic sweet potato plants. ABA, proline, and K⁺ contents were significantly increased, whereas malondialdehyde (MDA), Na⁺ and H₂O₂ contents and O₂⁻ production rate were significantly decreased in the transgenic plants under salt, drought, and cold stresses. Overexpression of the gene up-regulated genes involved in ABA biosynthesis, stress response, and stomatal closure; increased enzyme activities in the reactive oxygen species (ROS) scavenging system; and controlled stomatal closure under salt, drought, and cold stresses. These results show that the IbSnRK1 gene confers salt, drought, and cold tolerance in sweet potato by activating the ROS scavenging system and controlling stomatal closure via the ABA signaling pathway.