IbNF-YA1 is a key factor in the storage root development of sweet potato.

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.

IbMYB73 targets abscisic acid-responsive IbGER5 to regulate root growth and stress tolerance in sweet potato.

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.

Genome-wide identification and expression analysis of the KNOX family and its diverse roles in response to growth and abiotic tolerance in sweet potato and its two diploid relatives.

KNOXs, a type of homeobox genes that encode atypical homeobox proteins, play an essential role in the regulation of growth and development, hormonal response, and abiotic stress in plants. However, the KNOX gene family has not been explored in sweet potato. In this study, through sequence alignment, genomic structure analysis, and phylogenetic characterization, 17, 12 and 11 KNOXs in sweet potato (I. batatas, 2n = 6x = 90) and its two diploid relatives I. trifida (2n = 2x = 30) and I. triloba (2n = 2x = 30) were identified. The protein physicochemical properties, chromosome localization, phylogenetic relationships, gene structure, protein interaction network, cis-elements of promoters, tissue-specific expression and expression patterns under hormone treatment and abiotic stresses of these 40 KNOX genes were systematically studied. IbKNOX4, -5, and - 6 were highly expressed in the leaves of the high-yield varieties Longshu9 and Xushu18. IbKNOX3 and IbKNOX8 in Class I were upregulated in initial storage roots compared to fibrous roots. IbKNOXs in Class M were specifically expressed in the stem tip and hardly expressed in other tissues. Moreover, IbKNOX2 and - 6, and their homologous genes were induced by PEG/mannitol and NaCl treatments. The results showed that KNOXs were involved in regulating growth and development, hormone crosstalk and abiotic stress responses between sweet potato and its two diploid relatives. This study provides a comparison of these KNOX genes in sweet potato and its two diploid relatives and a theoretical basis for functional studies.

The B-box transcription factor IbBBX29 regulates leaf development and flavonoid biosynthesis in sweet potato.

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.

IbMYC2 Contributes to Salt and Drought Stress Tolerance via Modulating Anthocyanin Accumulation and ROS-Scavenging System in Sweet Potato.

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 (H2O2), 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.

IbNIEL-mediated degradation of IbNAC087 regulates jasmonic acid-dependent salt and drought tolerance in sweet potato.

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.

IbBBX24 Promotes the Jasmonic Acid Pathway and Enhances Fusarium Wilt Resistance in Sweet Potato.

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.

Genome-Wide Identification and Expression Analysis of ACTIN Family Genes in the Sweet Potato and Its Two Diploid Relatives.

ACTINs are structural proteins widely distributed in plants. They are the main components of microfilaments and participate in many crucial physiological activities, including the maintenance of cell shape and cytoplasmic streaming. Meanwhile, ACTIN, as a housekeeping gene, is widely used in qRT-PCR analyses of plants. However, ACTIN family genes have not been explored in the sweet potato. In this study, we identified 30, 39, and 44 ACTINs in the 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, via analysis of their genome structure and by phylogenetic characterization. These ACTINs were divided into six subgroups according to their phylogenetic relationships with Arabidopsis thaliana. The physiological properties of the protein, chromosome localization, phylogenetic relationship, gene structure, promoter cis-elements, protein interaction networks, and expression patterns of these 113 ACTINs were systematically investigated. The results suggested that homologous ACTINs are differentiated in the sweet potato and its two diploid relatives, and play various vital roles in plant growth, tuberous root development, hormone crosstalk, and abiotic stress responses. Some stable ACTINs that could be used as internal reference genes were found in the sweet potato and its two diploid relatives, e.g., IbACTIN18, -20, and -16.2; ItfACTIN2.2, -16, and -10; ItbACTIN18 and -19.1. This work provides a comprehensive comparison and furthers our understanding of the ACTIN 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 potatoes.

Genome-Wide Identification and Expression Analysis of the Sucrose Synthase Gene Family in Sweet Potato and Its Two Diploid Relatives.

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, 2n = 6x = 90) as well as its two diploid wild relatives I. trifida (2n = 2x = 30) and I. triloba (2n = 2x = 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.

Genome-Wide Characterization of the PIFs Family in Sweet Potato and Functional Identification of IbPIF3.1 under Drought and Fusarium Wilt Stresses.

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, H2O2, 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.

The IbPYL8-IbbHLH66-IbbHLH118 complex mediates the abscisic acid-dependent drought response in 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.

The IbBBX24-IbTOE3-IbPRX17 module enhances abiotic stress tolerance by scavenging reactive oxygen species in 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 H2 O2 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.

Production and characterization of a novel interspecific somatic hybrid combining drought tolerance and high quality of sweet potato and Ipomoea triloba L.

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.

Genome-Wide Identification and Characterization of CDPK Family Reveal Their Involvements in Growth and Development and Abiotic Stress in Sweet Potato and Its Two Diploid Relatives.

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 CDPKs 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.

Genome-Wide Identification and Expression Analysis of SWEET Family Genes in Sweet Potato and Its Two Diploid Relatives.

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.

A Novel WRKY Transcription Factor from Ipomoea trifida, ItfWRKY70, Confers Drought Tolerance in Sweet Potato.

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 H2O2 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.

Genome-Wide Identification and Expression Analysis of JAZ Family Involved in Hormone and Abiotic Stress in Sweet Potato and Its Two Diploid Relatives.

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 JAZs 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.

A sucrose non-fermenting-1-related protein kinase-1 gene, IbSnRK1, improves starch content, composition, granule size, degree of crystallinity and gelatinization in transgenic sweet potato.

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.

A non-tandem CCCH-type zinc-finger protein, IbC3H18, functions as a nuclear transcriptional activator and enhances abiotic stress tolerance in sweet potato.

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, H2 O2 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.

A novel sweetpotato bZIP transcription factor gene, IbbZIP1, is involved in salt and drought tolerance in transgenic Arabidopsis.

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 H2O2 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.