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Sweet potato starch is in high demand globally for food and industry. However, starch content is negatively correlated with fresh yield. It is urgent to uncover the genetic basis and molecular mechanisms underlying the starch yield of sweet potato. Here we systematically explore source-sink synergy-mediated sweet potato starch yield formation: the production, loading, and transport of photosynthates in leaves, as well as their unloading and allocation in storage roots, lead to starch content divergence between sweet potato varieties. Moreover, we find that six haplotypes of IbPMA1 encoding a plasma membrane H + -ATPase are significantly linked with starch accumulation. Overexpression of IbPMA1 in sweet potato results in significantly increased starch and sucrose contents, while its knockdown exhibits an opposing effect. Furthermore, a basic helix-loop-helix (bHLH) transcription factor IbbHLH49 directly targets IbPMA1 and activates its transcription. Overexpression of IbbHLH49 notably improves source-sink synergy-mediated fresh yield and starch accumulation in sweet potato. Both IbbHLH49 and IbPMA1 substantially influence sugar transport and starch biosynthesis in source and sink tissues. These findings expand our understanding of starch yield formation and provide strategies and candidate genes for high starch breeding in root and tuber crops., (© 2024. The Author(s).)

As a major worldwide root crop, the mechanism underlying storage root yield formation has always been a hot topic in sweet potato [Ipomoea batatas (L.) Lam.]. Previously, we conducted the transcriptome database of differentially expressed genes between the cultivated sweet potato cultivar "Xushu18," its diploid wild relative Ipomoea triloba without storage root, and their interspecific somatic hybrid XT1 with medium-sized storage root. We selected one of these candidate genes, IbNF-YA1, for subsequent analysis. IbNF-YA1 encodes a nuclear transcription factor Y subunit alpha (NF-YA) gene, which is significantly induced by the natural auxin indole-3-acetic acid (IAA). The storage root yield of the IbNF-YA1 overexpression (OE) plant decreased by 29.15-40.22% compared with the wild type, while that of the RNAi plant increased by 10.16-21.58%. Additionally, IAA content increased significantly in OE plants. Conversely, the content of IAA decreased significantly in RNAi plants. Furthermore, real-time quantitative reverse transcription-PCR (qRT-PCR) analysis demonstrated that the expressions of the key genes IbYUCCA2, IbYUCCA4, and IbYUCCA8 in the IAA biosynthetic pathway were significantly changed in transgenic plants. The results indicated that IbNF-YA1 could directly target IbYUCCA4 and activate IbYUCCA4 transcription. The IAA content of IbYUCCA4 OE plants increased by 71.77-98.31%. Correspondingly, the storage root yield of the IbYUCCA4 OE plant decreased by 77.91-80.52%. These findings indicate that downregulating the IbNF-YA1 gene could improve the storage root yield in sweet potato., (© 2024 Society for Experimental Biology and John Wiley & Sons Ltd.)

Basic helix-loop-helix (bHLH) transcription factors extensively affect various physiological processes in plant metabolism, growth, and abiotic stress. However, the regulation mechanism of bHLH transcription factors in balancing anthocyanin biosynthesis and abiotic stress in sweet potato ( Ipomoea batata (L.) Lam.) remains unclear. Previously, transcriptome analysis revealed the genes that were differentially expressed among the purple-fleshed sweet potato cultivar 'Jingshu 6' and its anthocyanin-rich mutant 'JS6-5'. Here, we selected one of these potential genes, IbMYC2 , which belongs to the bHLH transcription factor family, for subsequent analyses. The expression of IbMYC2 in the JS6-5 storage roots is almost four-fold higher than Jingshu 6 and significantly induced by hydrogen peroxide (H 2 O 2 ), methyl jasmonate (MeJA), NaCl, and polyethylene glycol (PEG)6000. Overexpression of IbMYC2 significantly enhances anthocyanin production and exhibits a certain antioxidant capacity, thereby improving salt and drought tolerance. In contrast, reducing IbMYC2 expression increases its susceptibility. Our data showed that IbMYC2 could elevate the expression of anthocyanin synthesis pathway genes by binding to IbCHI and IbDFR promoters. Additionally, overexpressing IbMYC2 activates genes encoding reactive oxygen species (ROS)-scavenging and proline synthesis enzymes under salt and drought conditions. Taken together, these results demonstrate that the IbMYC2 gene exercises a significant impact on crop quality and stress resistance.

Sweet potato (Ipomoea batatas [L.] Lam.) is a crucial staple and bioenergy crop. Its abiotic stress tolerance holds significant importance in fully utilizing marginal lands. Transcriptional processes regulate abiotic stress responses, yet the molecular regulatory mechanisms in sweet potato remain unclear. In this study, a NAC (NAM, ATAF1/2, and CUC2) transcription factor, IbNAC087, was identified, which is commonly upregulated in salt- and drought-tolerant germplasms. Overexpression of IbNAC087 increased salt and drought tolerance by increasing jasmonic acid (JA) accumulation and activating reactive oxygen species (ROS) scavenging, whereas silencing this gene resulted in opposite phenotypes. JA-rich IbNAC087-OE (overexpression) plants exhibited more stomatal closure than wild-type (WT) and IbNAC087-Ri plants under NaCl, polyethylene glycol, and methyl jasmonate treatments. IbNAC087 functions as a nuclear transcriptional activator and directly activates the expression of the key JA biosynthesis-related genes lipoxygenase (IbLOX) and allene oxide synthase (IbAOS). Moreover, IbNAC087 physically interacted with a RING-type E3 ubiquitin ligase NAC087-INTERACTING E3 LIGASE (IbNIEL), negatively regulating salt and drought tolerance in sweet potato. IbNIEL ubiquitinated IbNAC087 to promote 26S proteasome degradation, which weakened its activation on IbLOX and IbAOS. The findings provide insights into the mechanism underlying the IbNIEL-IbNAC087 module regulation of JA-dependent salt and drought response in sweet potato and provide candidate genes for improving abiotic stress tolerance in crops., (© 2024 The Authors. Journal of Integrative Plant Biology published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.)

Root development influences plant responses to environmental conditions, and well-developed rooting enhances plant survival under abiotic stress. However, the molecular and genetic mechanisms underlying root development and abiotic stress tolerance in plants remain unclear. In this study, we identified the MYB transcription factor-encoding gene IbMYB73 by cDNA-amplified fragment length polymorphism and RNA-seq analyses. IbMYB73 expression was greatly suppressed under abiotic stress in the roots of the salt-tolerant sweet potato (Ipomoea batatas) line ND98, and its promoter activity in roots was significantly reduced by abscisic acid (ABA), NaCl, and mannitol treatments. Overexpression of IbMYB73 significantly inhibited adventitious root growth and abiotic stress tolerance, whereas IbMYB73-RNAi plants displayed the opposite pattern. IbMYB73 influenced the transcription of genes involved in the ABA pathway. Furthermore, IbMYB73 formed homodimers and activated the transcription of ABA-responsive protein IbGER5 by binding to an MYB binding sites I motif in its promoter. IbGER5 overexpression significantly inhibited adventitious root growth and abiotic stress tolerance concomitantly with a reduction in ABA content, while IbGER5-RNAi plants showed the opposite effect. Collectively, our results demonstrated that the IbMYB73-IbGER5 module regulates ABA-dependent adventitious root growth and abiotic stress tolerance in sweet potato, which provides candidate genes for the development of elite crop varieties with well-developed root-mediated abiotic stress tolerance., Competing Interests: Conflict of interest statement. None declared., (© American Society of Plant Biologists 2023. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Sweet potato ( Ipomoea batatas (L.) Lam.) is one of the most important food, feed, industrial raw materials, and new energy crops, and is widely cultivated around the world. China is the largest sweet potato producer in the world, and the sweet potato industry plays an important role in China's agriculture. During the growth of sweet potato, it is often affected by biotic stresses, such as fungi, nematodes, insects, viruses, and bacteria. These stressors are widespread worldwide and have severely restricted the production of sweet potato. In recent years, with the rapid development and maturity of biotechnology, an increasing number of stress-related genes have been introduced into sweet potato, which improves its quality and resistance of sweet potato. This paper summarizes the discovery of biological stress-related genes in sweet potato and the related mechanisms of stress resistance from the perspectives of genomics analysis, transcriptomics analysis, genetic engineering, and physiological and biochemical indicators. The mechanisms of stress resistance provide a reference for analyzing the molecular breeding of disease resistance mechanisms and biotic stress resistance in sweet potato.

Sucrose synthases (SUS; EC 2.4.1.13) encoded by a small multigene family are the central system of sucrose metabolism and have important implications for carbon allocation and energy conservation in nonphotosynthetic cells of plants. Though the SUS family genes ( SUSs ) have been identified in several plants, they have not been explored in sweet potato. In this research, nine, seven and seven SUSs were identified in the cultivated sweet potato ( Ipomoea batatas , 2 n = 6 x = 90) as well as its two diploid wild relatives I. trifida (2 n = 2 x = 30) and I. triloba (2 n = 2 x = 30), respectively, and divided into three subgroups according to their phylogenetic relationships. Their protein physicochemical properties, chromosomal localization, phylogenetic relationship, gene structure, promoter cis -elements, protein interaction network and expression patterns were systematically analyzed. The results indicated that the SUS gene family underwent segmental and tandem duplications during its evolution. The SUSs were highly expressed in sink organs. The IbSUSs especially IbSUS2 , IbSUS5 and IbSUS7 might play vital roles in storage root development and starch biosynthesis. The SUSs could also respond to drought and salt stress responses and take part in hormone crosstalk. This work provides new insights for further understanding the functions of SUSs and candidate genes for improving yield, starch content, and abiotic stress tolerance in sweet potatoes.

Phytochrome-interacting factors (PIFs) are essential for plant growth, development, and defense responses. However, research on the PIFs in sweet potato has been insufficient to date. In this study, we identified PIF genes in the cultivated hexaploid sweet potato ( Ipomoea batatas ) and its two wild relatives, Ipomoea triloba , and Ipomoea trifida . Phylogenetic analysis revealed that IbPIFs could be divided into four groups, showing the closest relationship with tomato and potato. Subsequently, the PIFs protein properties, chromosome location, gene structure, and protein interaction network were systematically analyzed. RNA-Seq and qRT-PCR analyses showed that IbPIFs were mainly expressed in stem, as well as had different gene expression patterns in response to various stresses. Among them, the expression of IbPIF3.1 was strongly induced by salt, drought, H 2 O 2 , cold, heat, Fusarium oxysporum f. sp. batatas ( Fob ), and stem nematodes, indicating that IbPIF3.1 might play an important role in response to abiotic and biotic stresses in sweet potato. Further research revealed that overexpression of IbPIF3 .1 significantly enhanced drought and Fusarium wilt tolerance in transgenic tobacco plants. This study provides new insights for understanding PIF-mediated stress responses and lays a foundation for future investigation of sweet potato PIFs.

Plant flavonoids are valuable natural antioxidants. Sweet potato (Ipomoea batatas) leaves are rich in flavonoids, regenerate rapidly, and can adapt to harsh environments, making them an ideal material for flavonoid biofortification. Here, we demonstrate that the B-box (BBX) family transcription factor IbBBX29 regulates the flavonoid contents and development of sweet potato leaves. IbBBX29 was highly expressed in sweet potato leaves and significantly induced by auxin (IAA). Overexpression of IbBBX29 contributed to a 21.37%-70.94% increase in leaf biomass, a 12.08%-21.85% increase in IAA levels, and a 31.33%-63.03% increase in flavonoid accumulation in sweet potato, whereas silencing this gene produced opposite effects. Heterologous expression of IbBBX29 in Arabidopsis (Arabidopsis thaliana) led to a dwarfed phenotype, along with enhanced IAA and flavonoid accumulation. RNA-seq analysis revealed that IbBBX29 modulates the expression of genes involved in the IAA signaling and flavonoid biosynthesis pathways. Chromatin immunoprecipitation-quantitative polymerase chain reaction and electrophoretic mobility shift assay indicated that IbBBX29 targets key genes of IAA signaling and flavonoid biosynthesis to activate their expression by binding to specific T/G-boxes in their promoters, especially those adjacent to the transcription start site. Moreover, IbBBX29 physically interacted with developmental and phenylpropanoid biosynthesis-related proteins, such as AGAMOUS-LIKE 21 protein IbAGL21 and MYB308-like protein IbMYB308L. Finally, overexpressing IbBBX29 also increased flavonoid contents in sweet potato storage roots. These findings indicate that IbBBX29 plays a pivotal role in regulating IAA-mediated leaf development and flavonoid biosynthesis in sweet potato and Arabidopsis, providing a candidate gene for flavonoid biofortification in plants., (© American Society of Plant Biologists 2022. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Sugar Will Eventually be Exported Transporter (SWEET) proteins are key transporters in sugar transportation. They are involved in the regulation of plant growth and development, hormone crosstalk, and biotic and abiotic stress responses. However, SWEET family genes have not been explored in the sweet potato. In this study, we identified 27, 27, and 25 SWEETs in cultivated hexaploid sweet potato ( Ipomoea batatas , 2n = 6x = 90) and its two diploid relatives, Ipomoea trifida (2n = 2x = 30) and Ipomoea triloba (2n = 2x = 30), respectively. These SWEETs were divided into four subgroups according to their phylogenetic relationships with Arabidopsis . The protein physiological properties, chromosome localization, phylogenetic relationships, gene structures, promoter cis -elements, protein interaction networks, and expression patterns of these 79 SWEETs were systematically investigated. The results suggested that homologous SWEETs are differentiated in sweet potato and its two diploid relatives and play various vital roles in plant growth, tuberous root development, carotenoid accumulation, hormone crosstalk, and abiotic stress response. This work provides a comprehensive comparison and furthers our understanding of the SWEET genes in the sweet potato and its two diploid relatives, thereby supplying a theoretical foundation for their functional study and further facilitating the molecular breeding of sweet potato.

Drought limits crop development and yields. bHLH (basic helix-loop-helix) transcription factors play critical roles in regulating the drought response in many plants, but their roles in this process in sweet potato are unknown. Here, we report that two bHLH proteins, IbbHLH118 and IbbHLH66, play opposite roles in the ABA-mediated drought response in sweet potato. ABA treatment repressed IbbHLH118 expression but induced IbbHLH66 expression in the drought-tolerant sweet potato line Xushu55-2. Overexpressing IbbHLH118 reduced drought tolerance, whereas overexpressing IbbHLH66 enhanced drought tolerance, in sweet potato. IbbHLH118 directly binds to the E-boxes in the promoters of ABA-insensitive 5 (IbABI5), ABA-responsive element binding factor 2 (IbABF2) and tonoplast intrinsic protein 1 (IbTIP1) to suppress their transcription. IbbHLH118 forms homodimers with itself or heterodimers with IbbHLH66. Both of the IbbHLHs interact with the ABA receptor IbPYL8. ABA accumulates under drought stress, promoting the formation of the IbPYL8-IbbHLH66-IbbHLH118 complex. This complex interferes with IbbHLH118's repression of ABA-responsive genes, thereby activating ABA responses and enhancing drought tolerance. These findings shed light on the role of the IbPYL8-IbbHLH66-IbbHLH118 complex in the ABA-dependent drought response of sweet potato and identify candidate genes for developing elite crop varieties with enhanced drought tolerance., (© 2022 The Authors. New Phytologist © 2022 New Phytologist Foundation.)

Sweet potato (Ipomoea batatas), an important root crop, has storage roots rich in starch that are edible and serve as a raw material in bioenergy production. Increasing the storage-root starch contents is a key sweet potato breeding goal. Phosphoglucomutase (PGM) is the catalytic enzyme for the interconversion of glucose-6-phosphate and glucose-1-phosphate, precursors in the plant starch synthetic pathway. Plant PGMs have plastidial and cytosolic isoforms, based on their subcellular localization. Here, IbpPGM , containing 22 exons and 21 introns, was cloned from the sweet potato line Xu 781. This gene was highly expressed in the storage roots and leaves, and its expression was induced by exogenous sucrose treatments. The mature IbpPGM protein was successfully expressed in Escherichia coli when a 73-aa chloroplastic transit peptide detected in the N-terminus was excised. The subcellular localization confirmed that IbpPGM was localized to the chloroplasts. The low-starch sweet potato cultivar Lizixiang IbpPGM -overexpression lines showed significantly increased starch, glucose, and fructose levels but a decreased sucrose level. Additionally, the expression levels of the starch synthetic pathway genes in the storage roots were up-regulated to different extents. Thus, IbpPGM significantly increased the starch content of the sweet potato storage roots, which makes it a candidate gene for the genetic engineering of the sweet potato.

Key Message: A novel interspecific somatic hybrid combining drought tolerance and high quality of sweet potato and Ipomoea triloba L. was obtained and its genetic and epigenetic variations were studied. Somatic hybridization can be used to overcome the cross-incompatibility between sweet potato (Ipomoea batatas (L.) Lam.) and its wild relatives and transfer useful and desirable genes from wild relatives to cultivated plants. However, most of the interspecific somatic hybrids obtained to date cannot produce storage roots and do not exhibit agronomic characters. In the present study, a novel interspecific somatic hybrid, named XT1, was obtained through protoplast fusion between sweet potato cv. Xushu 18 and its wild relative I. triloba. This somatic hybrid produced storage roots and exhibited significantly higher drought tolerance and quality compared with its cultivated parent Xushu 18. Transcriptome and real-time quantitative PCR (qRT-PCR) analyses revealed that the well-known drought stress-responsive genes in XT1 and I. triloba were significantly up-regulated under drought stress. The genomic structural reconstructions between the two genomes of the fusion parents in XT1 were confirmed using genomic in situ hybridization (GISH) and specific nuclear and cytoplasmic DNA markers. The DNA methylation variations were characterized by methylation-sensitive amplified polymorphism (MSAP). This study not only reveals the significance of somatic hybridization in the genetic improvement of sweet potato but also provides valuable materials and knowledge for further investigating the mechanism of storage root formation in sweet potato., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Sweet potato ( Ipomoea batatas (L.) Lam) is one of the most crucial food crops widely cultivated worldwide. In plants, MYB transcription factors play crucial roles in plant growth, defense regulation, and stress resistance. However, the regulatory mechanism of MYBs in salt and drought response remain poorly studied in sweet potato. By screening a transcriptome database for differentially expressed genes between the sweet potato variety Jingshu 6 and its mutant JS6-5 with high anthocyanin and increased tolerance to salt and drought stresses, we identified a R2R3-MYB gene IbMYB48 , for which expression was induced by PEG6000, NaCl, abscisic acid (ABA), methyl jasmonic acid (MeJA), salicylic acid (SA) and H 2 O 2 . Particle-mediated transient transformation of onion epidermal cells showed IbMYB48 is localized in the nucleus. Transactivation activity assay in yeast cells revealed that IbMYB48 has transactivation activity, and its active domain is located in the carboxyl (C)-terminal region. Furthermore, expression of IbMYB48 confers enhanced tolerance to salt and drought stresses in transgenic Arabidopsis. The contents of endogenous ABA, JA, and proline in transgenic lines were higher than control, and the activity of superoxide dismutase (SOD) was significantly increased under salt and drought stress conditions. By contrast, the accumulation of malondialdehyde (MDA) and H 2 O 2 were lower. Moreover, genes encoding enzymes involved in ABA biosynthetic pathway, JA biosynthesis and signaling pathway, and reactive oxygen species (ROS) scavenging system were significantly up-regulated in transgenic Arabidopsis under salt or drought stress. Altogether, these results suggest IbMYB48 may be a candidate gene for improvement of abiotic stress tolerance.

The cytochrome P450 superfamily (CYP450) is one of the largest protein families in plants, and its members play diverse roles in primary and secondary metabolic biosynthesis. In this study, the CYP450 family gene IbCYP82D47 was cloned from the high carotenoid line HVB-3 of sweet potato (Ipomoea batatas). The IbCYP82D47 protein harbored two transmembrane domains and dynamically localized between plastid stroma and membrane. Overexpression of IbCYP82D47 not only increased total carotenoid, lutein, zeaxanthin and violaxanthin contents by 32.2-48.0%, 10.5-13.3%, 40.2-136% and 82.4-106%, respectively, but also increased the number of carotenoid globules in sweet potato storage roots. Furthermore, genes associated with the carotenoid biosynthesis (IbDXS, IbPSY, IbLCYE, IbBCH, IbZEP) were upregulated in transgenic sweet potato. In addition, IbCYP82D47 physically interacts with geranylgeranyl diphosphate synthase 12 (IbGGPPS12). Our findings suggest that IbCYP82D47 increases carotenoid contents by interacting with the carotenoid biosynthesis related protein IbGGPPS12, and influencing the expressions of carotenoid biosynthesis related genes in transgenic sweet potato., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Calcium-dependent protein kinase (CDPKs) is one of the calcium-sensing proteins in plants. They are likely to play important roles in growth and development and abiotic stress responses. However, these functions have not been explored in sweet potato. In this study, we identified 39 CDPK s in cultivated hexaploid sweet potato ( Ipomoea batatas , 2n = 6x = 90), 35 CDPKs in diploid relative Ipomoea trifida (2n = 2x = 30), and 35 CDPKs in Ipomoea triloba (2n = 2x = 30) via genome structure analysis and phylogenetic characterization, respectively. The protein physiological property, chromosome localization, phylogenetic relationship, gene structure, promoter cis -acting regulatory elements, and protein interaction network were systematically investigated to explore the possible roles of homologous CDPKs in the growth and development and abiotic stress responses of sweet potato. The expression profiles of the identified CDPKs in different tissues and treatments revealed tissue specificity and various expression patterns in sweet potato and its two diploid relatives, supporting the difference in the evolutionary trajectories of hexaploid sweet potato. These results are a critical first step in understanding the functions of sweet potato CDPK genes and provide more candidate genes for improving yield and abiotic stress tolerance in cultivated sweet potato.

Soil salinity and drought limit sweet potato yield. Scavenging of reactive oxygen species (ROS) by peroxidases (PRXs) is essential during plant stress responses, but how PRX expression is regulated under abiotic stress is not well understood. Here, we report that the B-box (BBX) family transcription factor IbBBX24 activates the expression of the class III peroxidase gene IbPRX17 by binding to its promoter. Overexpression of IbBBX24 and IbPRX17 significantly improved the tolerance of sweet potato to salt and drought stresses, whereas reducing IbBBX24 expression increased their susceptibility. Under abiotic stress, IbBBX24- and IbPRX17-overexpression lines showed higher peroxidase activity and lower H 2 O 2 accumulation compared with the wild-type. RNA sequencing analysis revealed that IbBBX24 modulates the expression of genes encoding ROS scavenging enzymes, including PRXs. Moreover, interaction between IbBBX24 and the APETALA2 (AP2) protein IbTOE3 enhances the ability of IbBBX24 to activate IbPRX17 transcription. Overexpression of IbTOE3 improved the tolerance of tobacco plants to salt and drought stresses by scavenging ROS. Together, our findings elucidate the mechanism underlying the IbBBX24-IbTOE3-IbPRX17 module in response to abiotic stress in sweet potato and identify candidate genes for developing elite crop varieties with enhanced abiotic stress tolerance., (© 2021 The Authors. New Phytologist © 2021 New Phytologist Foundation.)

WRKY transcription factors are one of the important families in plants, and have important roles in plant growth, abiotic stress responses, and defense regulation. In this study, we isolated a WRKY gene, ItfWRKY70 , from the wild relative of sweet potato Ipomoea trifida (H.B.K.) G. Don. This gene was highly expressed in leaf tissue and strongly induced by 20% PEG6000 and 100 μM abscisic acid (ABA). Subcellar localization analyses indicated that ItfWRKY70 was localized in the nucleus. Overexpression of ItfWRKY70 significantly increased drought tolerance in transgenic sweet potato plants. The content of ABA and proline, and the activity of SOD and POD were significantly increased, whereas the content of malondialdehyde (MDA) and H 2 O 2 were decreased in transgenic plants under drought stress. Overexpression of ItfWRKY70 up-regulated the genes involved in ABA biosynthesis, stress-response, ROS-scavenging system, and stomatal aperture in transgenic plants under drought stress. Taken together, these results demonstrated that ItfWRKY70 plays a positive role in drought tolerance by accumulating the content of ABA, regulating stomatal aperture and activating the ROS scavenging system in sweet potato.

Jasmonate ZIM-domain (JAZ) proteins are key repressors of a jasmonic acid signaling pathway. They play essential roles in the regulation of plant growth and development, as well as environmental stress responses. However, this gene family has not been explored in sweet potato. In this study, we identified 14, 15, and 14 JAZ s in cultivated hexaploid sweet potato ( Ipomoea batatas , 2n = 6x = 90), and its two diploid relatives Ipomoea trifida (2n = 2x = 30) and Ipomoea triloba (2n = 2x = 30), respectively. These JAZs were divided into five subgroups according to their phylogenetic relationships with Arabidopsis . The protein physiological properties, chromosome localization, phylogenetic relationship, gene structure, promoter cis -elements, protein interaction network, and expression pattern of these 43 JAZs were systematically investigated. The results suggested that there was a differentiation between homologous JAZs , and each JAZ gene played different vital roles in growth and development, hormone crosstalk, and abiotic stress response between sweet potato and its two diploid relatives. Our work provided comprehensive comparison and understanding of the JAZ genes in sweet potato and its two diploid relatives, supplied a theoretical foundation for their functional study, and further facilitated the molecular breeding of sweet potato.

Arabidopsis Toxicos en Levadura (ATL) proteins compose a subfamily of E3 ubiquitin ligases and play major roles in regulating plant growth, cold, drought, oxidative stresses response and pathogen defense in plants. However, the role in enhancing salt tolerance has not been reported to date. Here, we cloned a novel RING-H2 type E3 ubiquitin ligase gene, named IbATL38, from sweetpotato cultivar Lushu 3. This gene was highly expressed in the leaves of sweetpotato and strongly induced by NaCl and abscisic acid (ABA). This IbATL38 was localized to nucleus and plasm membrane and possessed E3 ubiquitin ligase activity. Overexpression of IbATL38 in Arabidopsis significantly enhanced salt tolerance, along with inducible expression of a series of stress-responsive genes and prominently decrease of H 2 O 2 content. These results suggest that IbATL38 as a novel E3 ubiquitin ligase may play an important role in salt stress response., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)

Cultivated sweet potato ( Ipomoea batatas ) is an important source of food for both humans and domesticated animals. Here, we show that the B-box (BBX) family transcription factor IbBBX24 regulates the jasmonic acid (JA) pathway in sweet potato. When IbBBX24 was overexpressed in sweet potato, JA accumulation increased, whereas silencing this gene decreased JA levels. RNA sequencing analysis revealed that IbBBX24 modulates the expression of genes involved in the JA pathway. IbBBX24 regulates JA responses by antagonizing the JA signaling repressor IbJAZ10, which relieves IbJAZ10's repression of IbMYC2, a JA signaling activator. IbBBX24 binds to the IbJAZ10 promoter and activates its transcription, whereas it represses the transcription of IbMYC2 The interaction between IbBBX24 and IbJAZ10 interferes with IbJAZ10's repression of IbMYC2, thereby promoting the transcriptional activity of IbMYC2. Overexpressing IbBBX24 significantly increased Fusarium wilt disease resistance, suggesting that JA responses play a crucial role in regulating Fusarium wilt resistance in sweet potato. Finally, overexpressing IbBBX24 led to increased yields in sweet potato. Together, our findings indicate that IbBBX24 plays a pivotal role in regulating JA biosynthesis and signaling and increasing Fusarium wilt resistance and yield in sweet potato, thus providing a candidate gene for developing elite crop varieties with enhanced pathogen resistance but without yield penalty., (© 2020 American Society of Plant Biologists. All rights reserved.)

WRKYs play important roles in plant growth, defense regulation, and stress response. However, the mechanisms through which WRKYs are involved in drought and salt tolerance have been rarely characterized in sweetpotato [ Ipomoea batatas (L.) Lam.]. In this study, we cloned a WRKY gene, IbWRKY2 , from sweetpotato and its expression was induced with PEG6000, NaCl, and abscisic acid (ABA). The IbWRKY2 was localized in the nucleus. The full-length protein exhibited transactivation activity, and its active domain was located in the N-terminal region. IbWRKY2-overexpressing Arabidopsis showed enhanced drought and salt tolerance. After drought and salt treatments, the contents of ABA and proline as well as the activity of superoxide dismutase (SOD) were higher in transgenic plants, while the malondialdehyde (MDA) and H 2 O 2 contents were lower. In addition, several genes related to the ABA signaling pathway, proline biosynthesis, and the reactive oxygen species (ROS)-scavenging system, were significantly up-regulated in transgenic lines. These results demonstrate that IbWRKY2 confers drought and salt tolerance in Arabidopsis. Furthermore, IbWRKY2 was able to interact with IbVQ4, and the expression of IbVQ4 was induced by drought and salt treatments. These results provide clues regarding the mechanism by which IbWRKY2 contributes to the regulation of abiotic stress tolerance., Competing Interests: The authors declare no conflicts of interest.

Key Message: The overexpression of IbbZIP1 leads to a significant upregulation of abiotic-related genes, suggesting that IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. Basic region/leucine zipper motif (bZIP) transcription factors regulate flower development, seed maturation, pathogen defense, and stress signaling in plants. Here, we cloned a novel bZIP transcription factor gene, named IbbZIP1, from sweetpotato [Ipomoea batatas (L.) Lam.] line HVB-3. The full length of IbbZIP1 exhibited transactivation activity in yeast. The expression of IbbZIP1 in sweetpotato was strongly induced by NaCl, PEG6000, and abscisic acid (ABA). Its overexpression in Arabidopsis significantly enhanced salt and drought tolerance. Under salt and drought stresses, the transgenic Arabidopsis plants showed significant upregulation of the genes involved in ABA and proline biosynthesis and reactive oxygen species scavenging system, significant increase of ABA and proline contents and superoxide dismutase activity and significant decrease of H 2 O 2 content. These results demonstrate that the IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. This study provides a novel bZIP gene for improving the tolerance of sweetpotato and other plants to abiotic stresses.

CCCH-type zinc-finger proteins play essential roles in regulating plant development and stress responses. However, the molecular and functional properties of non-tandem CCCH-type zinc-finger (non-TZF) proteins have been rarely characterized in plants. Here, we report the biological and molecular characterization of a sweet potato non-TZF gene, IbC3H18. We show that IbC3H18 exhibits tissue- and abiotic stress-specific expression, and could be effectively induced by abiotic stresses, including NaCl, polyethylene glycol (PEG) 6000, H 2 O 2 and abscisic acid (ABA) in sweet potato. Accordingly, overexpression of IbC3H18 led to increased, whereas knock-down of IbC3H18 resulted in decreased tolerance of sweet potato to salt, drought and oxidation stresses. In addition, IbC3H18 functions as a nuclear transcriptional activator and regulates the expression of a range of abiotic stress-responsive genes involved in reactive oxygen species (ROS) scavenging, ABA signaling, photosynthesis and ion transport pathways. Moreover, our data demonstrate that IbC3H18 physically interacts with IbPR5, and that overexpression of IbPR5 enhances salt and drought tolerance in transgenic tobacco plants. Collectively, our data indicate that IbC3H18 functions in enhancing abiotic stress tolerance in sweet potato, which may serve as a candidate gene for use in improving abiotic stress resistance in crops., (© 2019 The Authors. New Phytologist © 2019 New Phytologist Trust.)

The manipulation of APETALA2/ethylene responsive factor (AP2/ERF) genes in plants makes great contributions on resistance to abiotic stresses. Here, we cloned an AP2/ERF gene from the salt-tolerant sweetpotato line ND98 and named IbRAP2-12. IbRAP2-12 protein expressed in nuclear revealed by transient expression in tobacco epidermal cells, and IbRAP2-12 exhibited transcriptional activation using heterologous expression assays in yeast. IbRAP2-12 was induced by NaCl (200 mM), 20% polyethylene glycol (PEG) 6000, 100 μM abscisic acid (ABA), 100 μM ethephon and 100 μM methyl jasmonate (MeJA). IbRAP2-12-overexpressing Arabidopsis lines were more tolerant to salt and drought stresses than wild type plants. Transcriptome analysis showed that genes involved in the ABA signalling, JA signalling, proline biosynthesis and reactive oxygen species (ROS) scavenging processes were up-regulated in IbRAP2-12 overexpression lines under salt and drought stresses. In comparing with WT, the contents of ABA, JA and proline were significantly increased, while hydrogen peroxide (H 2 O 2 ) and the rate of water loss were significantly reduced in transgenic lines under salt and drought stresses. All these results demonstrated the roles of IbRAP2-12 in enhancing salt and drought tolerance in transgenic Arabidopsis lines. Thus, this IbRAP2-12 gene can be used to increase the tolerance ability during abiotic stresses in plants., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Sucrose non-fermenting-1-related protein kinase-1 (SnRK1) is an essential energy-sensing regulator and plays a key role in the global control of carbohydrate metabolism. The SnRK1 gene has been found to increase starch accumulation in several plant species. However, its roles in improving starch quality have not been reported to date. In this study, we found that the IbSnRK1 gene was highly expressed in the storage roots of sweet potato and strongly induced by exogenous sucrose. Its expression followed the circandian rhythm. Its overexpression not only increased starch content, but also decreased proportion of amylose, enlarged granule size and improved degree of crystallinity and gelatinization in transgenic sweet potato, which revealed, for the first time, the important roles of SnRK1 in improving starch quality of plants. The genes involved in starch biosynthesis pathway were systematically up-regulated, and the content of ADP-glucose as an important precursor for starch biosynthesis and the activities of key enzymes were significantly increased in transgenic sweet potato. These findings indicate that IbSnRK1 improves starch content and quality through systematical up-regulation of the genes and the increase in key enzyme activities involved in starch biosynthesis pathway in transgenic sweet potato. This gene has the potential to improve starch content and quality in sweet potato and other plants., (© 2018 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

Lycopene β-cyclase (LCYB) is an essential enzyme that catalyzes the conversion of lycopene into α-carotene and β-carotene in carotenoid biosynthesis pathway. However, the roles and underlying mechanisms of the LCYB gene in plant responses to abiotic stresses are rarely known. This gene has not been used to improve carotenoid contents of sweetpotato, Ipomoea batatas (L.) Lam.. In the present study, a new allele of the LCYB gene, named IbLCYB2, was isolated from the storage roots of sweetpotato line HVB-3. Its overexpression significantly increased the contents of α-carotene, β-carotene, lutein, β-cryptoxanthin and zeaxanthin and enhanced the tolerance to salt, drought and oxidative stresses in the transgenic sweetpotato (cv. Shangshu 19) plants. The genes involved in carotenoid and abscisic acid (ABA) biosynthesis pathways and abiotic stress responses were up-regulated in the transgenic plants. The ABA and proline contents and superoxide dismutase (SOD) activity were significantly increased, whereas malonaldehyde (MDA) and H 2 O 2 contents were significantly decreased in the transgenic plants under abiotic stresses. The overall results indicate that the IbLCYB2 gene enhances carotenoid contents and abiotic stress tolerance through positive regulation of carotenoid and ABA biosynthesis pathways in sweetpotato. This gene has the potential to improve carotenoid contents and abiotic stress tolerance in sweetpotato and other plants., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Previously, we obtained the sweetpotato somatic hybrid KT1 from a cross between sweetpotato (Ipomoea batatas (L.) Lam.) cv. Kokei No. 14 and its drought-tolerant wild relative I. triloba L. KT1 not only inherited the thick storage root characteristic of Kokei No. 14 but also the drought-tolerance trait of I. triloba L. The aim of this study was to explore the molecular mechanism of the drought tolerance of KT1. Four-week-old in vitro-grown plants of KT1, Kokei No. 14, and I. triloba L. were subjected to a simulated drought stress treatment (30% PEG6000) for 0, 6, 12 and 24 h. Total RNA was extracted from samples at each time point, and then used for transcriptome sequencing. The gene transcript profiles of KT1 and its parents were compared to identify differentially expressed genes, and drought-related modules were screened by a weighted gene co-expression network analysis. The functions of ABI-like protein and Ca2+-ATPase, two proteins screened from the cyan and light yellow modules, were analyzed in terms of their potential roles in drought tolerance in KT1 and its parents. These analyses of the drought responses of KT1 and its somatic donors at the transcriptional level provide new annotations for the molecular mechanism of drought tolerance in the somatic hybrid KT1 and its parents.

ζ-Carotene desaturase (ZDS) is one of the key enzymes in carotenoid biosynthesis pathway. However, the ZDS gene has not been applied to carotenoid improvement of plants. Its roles in tolerance to abiotic stresses have not been reported. In this study, the IbZDS gene was isolated from storage roots of sweetpotato (Ipomoea batatas (L.) Lam.) cv. Nongdafu 14. Its overexpression significantly increased β-carotene and lutein contents and enhanced salt tolerance in transgenic sweetpotato (cv. Kokei No. 14) plants. Significant up-regulation of lycopene β-cyclase (β-LCY) and β-carotene hydroxylase (β-CHY) genes and significant down-regulation of lycopene ε-cyclase (ε-LCY) and ε-carotene hydroxylase (ε-CHY) genes were found in the transgenic plants. Abscisic acid (ABA) and proline contents and superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were significantly increased, whereas malonaldehyde (MDA) content was significantly decreased in the transgenic plants under salt stress. The salt stress-responsive genes encoding pyrroline-5-carboxylate reductase (P5CR), SOD, CAT, ascorbate peroxidase (APX) and POD were found to be significantly up-regulated in the transgenic plants under salt stress. This study indicates that the IbZDS gene has the potential to be applied for improving β-carotene and lutein contents and salt tolerance in sweetpotato and other plants., (Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.)

Soluble starch synthase I (SSI) is a key enzyme in the biosynthesis of plant amylopectin. In this study, the gene named IbSSI, was cloned from sweet potato, an important starch crop. A high expression level of IbSSI was detected in the leaves and storage roots of the sweet potato. Its overexpression significantly increased the content and granule size of starch and the proportion of amylopectin by up-regulating starch biosynthetic genes in the transgenic plants compared with wild-type plants (WT) and RNA interference plants. The frequency of chains with degree of polymerization (DP) 5-8 decreased in the amylopectin fraction of starch, whereas the proportion of chains with DP 9-25 increased in the IbSSI-overexpressing plants compared with WT plants. Further analysis demonstrated that IbSSI was responsible for the synthesis of chains with DP ranging from 9 to 17, which represents a different chain length spectrum in vivo from its counterparts in rice and wheat. These findings suggest that the IbSSI gene plays important roles in determining the content, composition, granule size and structure of starch in sweet potato. This gene may be utilized to improve the content and quality of starch in sweet potato and other plants.

Sweetpotato (Ipomoea batatas) is an autohexaploid species with 90 chromosomes (2n = 6x = 90) and a basic chromosome number of 15, and is therefore regarded as one of the most challenging species for high-density genetic map construction. Here, we used single nucleotide polymorphisms (SNPs) identified by double-digest restriction site-associated DNA sequencing based on next-generation sequencing technology to construct a map for sweetpotato. We then aligned the sequence reads onto the reference genome sequence of I. trifida, a likely diploid ancestor of sweetpotato, to detect SNPs. In addition, to simplify analysis of the complex genetic mode of autohexaploidy, we used an S1 mapping population derived from self-pollination of a single parent. As a result, 28,087 double-simplex SNPs showing a Mendelian segregation ratio in the S1 progeny could be mapped onto 96 linkage groups (LGs), covering a total distance of 33,020.4 cM. Based on the positions of the SNPs on the I. trifida genome, the LGs were classified into 15 groups, each with roughly six LGs and six small extra groups. The molecular genetic techniques used in this study are applicable to high-density mapping of other polyploid plant species, including important crops.

Sweet potato is an important food and bio-energy crop, and investigating the mechanisms underlying salt tolerance will provide information for salt-tolerant breeding of this crop. Here, the root transcriptomes of the salt-sensitive variety Lizixiang and the salt-tolerant line ND98 were compared to identify the genes and pathways involved in salt stress responses. In total, 8,744 and 10,413 differentially expressed genes (DEGs) in Lizixiang and ND98, respectively, were involved in salt responses. A lower DNA methylation level was detected in ND98 than in Lizixiang. In both genotypes, the DEGs, which function in phytohormone synthesis and signalling and ion homeostasis, may underlie the different degrees of salt tolerance. Significant up-regulations of the genes involved in the jasmonic acid (JA) biosynthesis and signalling pathways and ion transport, more accumulation of JA, a higher degree of stomatal closure and a lower level of Na + were found in ND98 compared to Lizixiang. This is the first report on transcriptome responses to salt tolerance in sweet potato. These results reveal that the JA signalling pathway plays important roles in the response of sweet potato to salt stress. This study provides insights into the mechanisms and genes involved in the salt tolerance of sweet potato.

Background: Sweetpotato, Ipomoea batatas (L.) Lam., is an important food crop widely grown in the world. However, little is known about the genome of this species because it is a highly heterozygous hexaploid. Gaining a more in-depth knowledge of sweetpotato genome is therefore necessary and imperative. In this study, the first bacterial artificial chromosome (BAC) library of sweetpotato was constructed. Clones from the BAC library were end-sequenced and analyzed to provide genome-wide information about this species., Results: The BAC library contained 240,384 clones with an average insert size of 101 kb and had a 7.93-10.82 × coverage of the genome, and the probability of isolating any single-copy DNA sequence from the library was more than 99%. Both ends of 8310 BAC clones randomly selected from the library were sequenced to generate 11,542 high-quality BAC-end sequences (BESs), with an accumulative length of 7,595,261 bp and an average length of 658 bp. Analysis of the BESs revealed that 12.17% of the sweetpotato genome were known repetitive DNA, including 7.37% long terminal repeat (LTR) retrotransposons, 1.15% Non-LTR retrotransposons and 1.42% Class II DNA transposons etc., 18.31% of the genome were identified as sweetpotato-unique repetitive DNA and 10.00% of the genome were predicted to be coding regions. In total, 3,846 simple sequences repeats (SSRs) were identified, with a density of one SSR per 1.93 kb, from which 288 SSRs primers were designed and tested for length polymorphism using 20 sweetpotato accessions, 173 (60.07%) of them produced polymorphic bands. Sweetpotato BESs had significant hits to the genome sequences of I. trifida and more matches to the whole-genome sequences of Solanum lycopersicum than those of Vitis vinifera, Theobroma cacao and Arabidopsis thaliana., Conclusions: The first BAC library for sweetpotato has been successfully constructed. The high quality BESs provide first insights into sweetpotato genome composition, and have significant hits to the genome sequences of I. trifida and more matches to the whole-genome sequences of Solanum lycopersicum. These resources as a robust platform will be used in high-resolution mapping, gene cloning, assembly of genome sequences, comparative genomics and evolution for sweetpotato.

Myo-inositol-1-phosphate synthase (MIPS) is a key rate limiting enzyme in myo-inositol biosynthesis. The MIPS gene has been shown to improve tolerance to abiotic stresses in several plant species. However, its role in resistance to biotic stresses has not been reported. In this study, we found that expression of the sweet potato IbMIPS1 gene was induced by NaCl, polyethylene glycol (PEG), abscisic acid (ABA) and stem nematodes. Its overexpression significantly enhanced stem nematode resistance as well as salt and drought tolerance in transgenic sweet potato under field conditions. Transcriptome and real-time quantitative PCR analyses showed that overexpression of IbMIPS1 up-regulated the genes involved in inositol biosynthesis, phosphatidylinositol (PI) and ABA signalling pathways, stress responses, photosynthesis and ROS-scavenging system under salt, drought and stem nematode stresses. Inositol, inositol-1,4,5-trisphosphate (IP3 ), phosphatidic acid (PA), Ca(2+) , ABA, K(+) , proline and trehalose content was significantly increased, whereas malonaldehyde (MDA), Na(+) and H2 O2 content was significantly decreased in the transgenic plants under salt and drought stresses. After stem nematode infection, the significant increase of inositol, IP3 , PA, Ca(2+) , ABA, callose and lignin content and significant reduction of MDA content were found, and a rapid increase of H2 O2 levels was observed, peaked at 1 to 2 days and thereafter declined in the transgenic plants. This study indicates that the IbMIPS1 gene has the potential to be used to improve the resistance to biotic and abiotic stresses in plants., (© 2015 Society for Experimental Biology, Association of Applied Biologists and John Wiley & Sons Ltd.)

Sweetpotato highly produces carotenoids in storage roots. In this study, a cDNA encoding geranylgeranyl phyrophosphate synthase (GGPS), named IbGGPS, was isolated from sweetpotato storage roots. Green fluorescent protein (GFP) was fused to the C-terminus of IbGGPS to obtain an IbGGPS-GFP fusion protein that was transiently expressed in both epidermal cells of onion and leaves of tobacco. Confocal microscopic analysis determined that the IbGGPS-GFP protein was localized to specific areas of the plasma membrane of onion and chloroplasts in tobacco leaves. The coding region of IbGGPS was cloned into a binary vector under the control of 35S promoter and then transformed into Arabidopsis thaliana to obtain transgenic plants. High performance liquid chromatography (HPLC) analysis showed a significant increase of total carotenoids in transgenic plants. The seeds of transgenic and wild-type plants were germinated on an agar medium supplemented with polyethylene glycol (PEG). Transgenic seedlings grew significantly longer roots than wild-type ones did. Further enzymatic analysis showed an increased activity of superoxide dismutase (SOD) in transgenic seedlings. In addition, the level of malondialdehyde (MDA) was reduced in transgenics. qRT-PCR analysis showed altered expressions of several genes involved in the carotenoid biosynthesis in transgenic plants. These data results indicate that IbGGPS is involved in the biosynthesis of carotenoids in sweetpotato storage roots and likely associated with tolerance to osmotic stress.

Agrobacterium rhizogenes and Agrobacterium tumefaciens are plant pathogenic bacteria capable of transferring DNA fragments [transfer DNA (T-DNA)] bearing functional genes into the host plant genome. This naturally occurring mechanism has been adapted by plant biotechnologists to develop genetically modified crops that today are grown on more than 10% of the world's arable land, although their use can result in considerable controversy. While assembling small interfering RNAs, or siRNAs, of sweet potato plants for metagenomic analysis, sequences homologous to T-DNA sequences from Agrobacterium spp. were discovered. Simple and quantitative PCR, Southern blotting, genome walking, and bacterial artificial chromosome library screening and sequencing unambiguously demonstrated that two different T-DNA regions (IbT-DNA1 and IbT-DNA2) are present in the cultivated sweet potato (Ipomoea batatas [L.] Lam.) genome and that these foreign genes are expressed at detectable levels in different tissues of the sweet potato plant. IbT-DNA1 was found to contain four open reading frames (ORFs) homologous to the tryptophan-2-monooxygenase (iaaM), indole-3-acetamide hydrolase (iaaH), C-protein (C-prot), and agrocinopine synthase (Acs) genes of Agrobacterium spp. IbT-DNA1 was detected in all 291 cultigens examined, but not in close wild relatives. IbT-DNA2 contained at least five ORFs with significant homology to the ORF14, ORF17n, rooting locus (Rol)B/RolC, ORF13, and ORF18/ORF17n genes of A. rhizogenes. IbT-DNA2 was detected in 45 of 217 genotypes that included both cultivated and wild species. Our finding, that sweet potato is naturally transgenic while being a widely and traditionally consumed food crop, could affect the current consumer distrust of the safety of transgenic food crops.

Salt stress is one of the major environmental stresses in agriculture worldwide and affects crop productivity and quality. The development of crops with elevated levels of salt tolerance is therefore highly desirable. In the present study, a novel maspardin gene, named IbMas, was isolated from salt-tolerant sweetpotato (Ipomoea batatas (L.) Lam.) line ND98. IbMas contains maspardin domain and belongs to α/β-hydrolase superfamily. Expression of IbMas was up-regulated in sweetpotato under salt stress and ABA treatment. The IbMas-overexpressing sweetpotato (cv. Shangshu 19) plants exhibited significantly higher salt tolerance compared with the wild-type. Proline content was significantly increased, whereas malonaldehyde content was significantly decreased in the transgenic plants. The activities of superoxide dismutase (SOD) and photosynthesis were significantly enhanced in the transgenic plants. H2O2 was also found to be significantly less accumulated in the transgenic plants than in the wild-type. Overexpression of IbMas up-regulated the salt stress responsive genes, including pyrroline-5-carboxylate synthase, pyrroline-5-carboxylate reductase, SOD, psbA and phosphoribulokinase genes, under salt stress. These findings suggest that overexpression of IbMas enhances salt tolerance of the transgenic sweetpotato plants by regulating osmotic balance, protecting membrane integrity and photosynthesis and increasing reactive oxygen species scavenging capacity.

Iron-sulfur cluster biosynthesis involving the nitrogen fixation (Nif) proteins has been proposed as a general mechanism acting in various organisms. NifU-like protein may play an important role in protecting plants against abiotic and biotic stresses. An iron-sulfur cluster scaffold protein gene, IbNFU1, was isolated from a salt-tolerant sweetpotato (Ipomoea batatas (L.) Lam.) line LM79 in our previous study, but its role in sweetpotato stress tolerance was not investigated. In the present study, the IbNFU1 gene was introduced into a salt-sensitive sweetpotato cv. Lizixiang to characterize its function in salt tolerance. The IbNFU1-overexpressing sweetpotato plants exhibited significantly higher salt tolerance compared with the wild-type. Proline and reduced ascorbate content were significantly increased, whereas malonaldehyde (MDA) content was significantly decreased in the transgenic plants. The activities of superoxide dismutase (SOD) and photosynthesis were significantly enhanced in the transgenic plants. H2O2 was also found to be significantly less accumulated in the transgenic plants than in the wild-type. Overexpression of IbNFU1 up-regulated pyrroline-5-carboxylate synthase (P5CS) and pyrroline-5-carboxylate reductase (P5CR) genes under salt stress. The systemic up-regulation of reactive oxygen species (ROS) scavenging genes was found in the transgenic plants under salt stress. These findings suggest that IbNFU1gene is involved in sweetpotato salt tolerance and enhances salt tolerance of the transgenic sweetpotato plants by regulating osmotic balance, protecting membrane integrity and photosynthesis and activating ROS scavenging system.