The transcription factor IbNAC29 positively regulates the carotenoid accumulation in sweet potato

Carotenoid is a tetraterpene pigment beneficial for human health.Although the carotenoid biosynthesis pathway has been extensively studied in plants,relatively little is known about their regulation in sweet potato.Previously,we conducted the transcriptome database of differentially expressed genes between the sweet potato(Ipomoea batatas)cultivar‘Weiduoli’and its high-carotenoid mutant‘HVB-3’.In this study,we selected one of these candidate genes,IbNAC29,for subsequent analyses.IbNAC29 belongs to the plant-specific NAC(NAM,ATAF1/2,and CUC2)transcription factor family.Relative IbNAC29 mRNA level in the HVB-3 storage roots was∼1.71-fold higher than Weiduoli.Additional experiments showed that the contents ofα-carotene,lutein,β-carotene,zeaxanthin,and capsanthin are obviously increased in the storage roots of transgenic sweet potato plants overexpressing IbNAC29.Moreover,the levels of carotenoid biosynthesis genes in transgenic plants were also up-regulated.Nevertheless,yeast one-hybrid assays indicated that IbNAC29 could not directly bind to the promoters of these carotenoid biosynthesis genes.Furthermore,the level of IbSGR1 was down-regulated,whose homologous genes in tomato can negatively regulate carotene accumulation.Yeast three-hybrid analysis revealed that the IbNAC29-IbMYB1R1-IbAITR5 could form a regulatory module.Yeast one-hybrid,electrophoretic mobility shift assay,quantitative PCR analysis of chromatin immunoprecipitation and dual-luciferase reporter assay showed that IbAITR5 directly binds to and inhibits the promoter activity of IbSGR1,up-regulating carotenoid biosynthesis gene IbPSY.Taken together,IbNAC29 is a potential candidate gene for the genetic improvement of nutritive value in sweet potato.

Construction of a high-density SSR genetic linkage map and identification of QTL for storage-root yield and dry-matter content in sweetpotato

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 highdensity 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.

Development of a high-density SSR genetic linkage map in sweet potato

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.

A sucrose non-fermenting-1-related protein kinase-1 gene, IbSnRK1, confers salt, drought and cold tolerance in 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 Na Cl,polyethylene glycol(PEG)6000,hydrogen peroxide(H2O2),cold(4°C),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.

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 biosynthesisrelated 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.

Harnessing wrinkling morphologies of graphene on soft substrates for mechanically programmable interfacial thermal conductance

Strain engineering has been leveraged to tune the thermal properties of materials by introducing stress and manipulating local atomic vibrations,which poses a detrimental threat to the mechanical integrity of materials and structures and limits the capability to regulate thermal transport.Here,we report that the interfacial thermal conductance of graphene on a soft substrate can be regulated by harnessing wrinkling and folding morphologies of graphene,which could be well controlled by managing the prestrain applied to the substrate.These obtained graphene structures are free of significant in-plane mechanical strain and only have infinitesimal distortion to the intrinsic thermal properties of graphene.The subsequent thermal transport studies with pumpprobe non-equilibrium molecular dynamics(MD)simulation show that the thermal conductance between graphene structures and the substrate is uniquely determined by the morphological features of graphene.The atomic density of interfacial interactions,energy dissipation,and temperature distribution are elucidated to understand the thermal transport across each graphene structure and substrate.We further demonstrate that the normalized thermal conductance decreases monotonically with the increase of the equivalent mechanical strain,showing the capability of mechanically programmable interfacial thermal conductance in a broad range of strains.Application demonstrations in search of on-demand thermal conductance are conducted by controlling the geometric morphologies of graphene.This study lays a foundation for regulating interfacial thermal conductance through mechanical loading-induced geometric deformation of materials on a soft substrate,potentially useful in the design of flexible and stretchable structures and devices with tunable thermal management performance.

A novel aldo-keto reductase gene, IbAKR, from sweet potato confers higher tolerance to cadmium stress in tobacco

High concentrations of Cd can inhibit growth and reduce the activity of the photosynthetic apparatus in plants. In several plant species, aldo-keto reductases(AKRs) have been shown to enhance tolerance to various abiotic stresses by scavenging cytotoxic aldehydes;however, few AKRs have been reported to enhance Cd stress tolerance. In this study, the gene Ib AKR was isolated from sweet potato. The relative expression levels of Ib AKR increased significantly(approximately 3-fold) after exposure to 200 mmol$L–1 Cd Cl2 or 10 mmol$L–1 H2 O2. A subcellular localization assay showed that Ib AKR is predominantly located in the nucleus and cytoplasm.Ib AKR-overexpressing tobacco plants showed higher tolerance to Cd stress than wild-type(WT). Transgenic lines showed a significant ability to scavenge malondialdehyde(MDA) and methylglyoxal(MG). In addition,proline content and superoxide dismutase activity were significantly higher and H2 O2 levels were significantly lower in the transgenic plants than in the WT. Quantitative real-time PCR analysis showed that the reactive oxygen species(ROS) scavenging genes encoding guaiacol peroxidase(GPX), ascorbate peroxidase(APX), monodehydroascorbate reductase(MDHAR) and peroxidase(POD) were significantly upregulated in transgenic plants compared to WT under Cd stress. These findings suggest that overexpressing Ib AKR enhances tolerance to Cd stress via the scavenging of cytotoxic aldehydes and the activation of the ROS scavenging system.

Comparative transcriptome analysis of purple-fleshed sweet potato provides insights into the molecular mechanism of anthocyanin biosynthesis

Sweet potato, Ipomoea batatas, is a globally important food crop. The purple-fleshed sweet potato, rich in anthocyanins, has great potential for both nutritional and pharmaceutical uses. In this study, we characterized the root transcriptomes of the purple-fleshed sweet potato cv.Jingshu 6 and its mutant JS6-5 with high anthocyanin content by high-throughput RNA sequencing. A total of22873364 and 27955097 high quality reads were obtained from Jingshu 6 and JS6-5, respectively, and assembled into35592 unigenes. In all, we obtained 1566 differentially expressed genes(DEGs). Among them, 994 were upregulated and 572 were downregulated in JS6-5 compared to the expression in Jingshu 6. A total of 1436 DEGs were annotated, in which 847 DEGs had gene ontology(GO) terms and 329 DEGs were assigned to 84 Kyoto Encyclopedia of Genes and Genomes(KEGG)pathways. Most importantly, 23 differentially expressed genes and 24 transcription factors were identified as candidate genes involved in anthocyanin biosynthesis. In addition, 2349 SSRs were detected. This study not only provides the candidate genes but also provides insights into the molecular mechanism of anthocyanin biosynthesis in sweet potato.