Genetic improvement of heat tolerance in wheat:Recent progress in understanding the underlying molecular mechanisms

As a cool season crop, wheat(Triticum aestivum L.) has an optimal daytime growing temperature of 15 ℃ during the reproductive stage. With global climate change, heat stress is becoming an increasingly severe constraint on wheat production. In this review, we summarize recent progress in understanding the molecular mechanisms of heat tolerance in wheat. We firstly describe the impact of heat tolerance on morphology and physiology and its potential effect on agronomic traits. We then review recent discoveries in determining the genetic and molecular factors affecting heat tolerance, including the effects of phytohormone signaling and epigenetic regulation. Finally, we discuss integrative strategies to improve heat tolerance by utilization of existing germplasm including modern cultivars, landraces and related species.

SNP-based identification of QTLs for thousand-grain weight and related traits in wheat 8762/Keyi 5214 DH lines

As important yield-related traits,thousand-grain weight(TGW),grain number per spike(GNS)and grain weight per spike(GWS)are crucial components of wheat production.To dissect their underlying genetic basis,a double haploid(DH)population comprised of 198 lines derived from 8762/Keyi 5214 was constructed.We then used genechip to genotype the DH population and integrated the yield-related traits TGW,GNS and GWS for QTL mapping.Finally,we obtained a total of 18942 polymorphic SNP markers and identified 41 crucial QTLs for these traits.Three stable QTLs for TGW were identified on chromosomes 2D(QTgw-2D.3 and QTgw-2D.4)and 6A(QTgw-6A.1),with additive alleles all from the parent 8762,explaining 4.81–18.67%of the phenotypic variations.Five stable QTLs for GNS on chromosomes 3D,5B,5D and 6A were identified.QGns-5D.1 was from parent 8762,while the other four QTLs were from parent Keyi 5214,explaining 5.89–7.08%of the GNS phenotypic variations.In addition,a stable GWS genetic locus QGws-4A.3 was detected from the parent 8762,which explained 6.08–6.14%of the phenotypic variations.To utilize the identified QTLs,we developed STARP markers for four important QTLs,Tgw2D.3-2,Tgw2D.4-1,Tgw6A.1 and Gns3D.1.Our results provide important basic resources and references for the identification and cloning of genes related to TGW,GNS and GWS in wheat.

Analysis of genetic diversity and population structure in sweetpotato using SSR markers

Sweetpotato, Ipomoea batatas(L.) Lam., is an important food crop worldwide. Large scale evaluation of sweetpotato germplasm for genetic diversity is necessary to determine the genetic relationships between them and effectively use them in the genetic improvement. In this study, the genetic diversity of 617 sweetpotato accessions, including 376landraces and 162 bred varieties from China and 79 introduced varieties from 11 other countries, was assessed using 30 simple sequence repeat(SSR) primer pairs with high polymorphism. Based on the population structure analysis,these sweetpotato accessions were divided into three groups, Group 1, Group 2 and Group 3, which included 228, 136and 253 accessions, respectively. Consistent results were obtained by phylogenic analysis and principal coordinate analysis(PCoA). Of the three groups, Group 2 showed the highest level of genetic diversity and its accessions were mainly distributed in low-latitude regions. The accessions from South China exhibited the highest level of genetic diversity, which supports the hypothesis that Fujian and Guangdong were the first regions where sweetpotato was introduced to China. Analysis of molecular variance(AMOVA) indicated significant genetic differentiations between the different groups, but low levels of genetic differentiation existed between the different origins and accession types.These results provide valuable information for the better utilization of these accessions in sweetpotato breeding.

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.

Molecular diversity and genetic structure of 380 sweetpotato accessions as revealed by SSR markers

Sweetpotato, Ipomoea batatas（L.） Lam., is an important food crop widely cultivated in the world. Evaluation of genetic relationships among diverse cultivars and landraces is necessary for efficient exploitation of genetic diversity in the existing germplasm resources. In the present study, a collection of 380 sweetpotato accessions assembled from different agro-climatic zones of China and other countries were genotyped using 30 SSR primer pairs. Model-based structure analysis separated the germplasm into three populations, P1, P2 and P3, containing 228, 133 and 19 accessions, respectively, which was consistent with the results of phylogenic and principal component analysis（PCA）. Analysis of molecular variance（AMOVA） revealed significant genetic differentiation among inferred populations, accounting for 16.47% of the total molecular variance, however, the differences between the regions were not significant, the total variation were due to the differences between the genotypes within the population. Pairwise fixation index（F ST） suggested that populations P1 and P3 had the highest differentiation, while populations P1 and P2 had the lowest differentiation. The diversity among populations was wide, which confirmed the genetic distinction of populations. Through comparing model-based structure and domestication-based classification, it was found that the accessions of population P1 mainly belonged to modern cultivars, and the accessions of populations P2 and P3 basically corresponded to landraces, by which we suggest that modern cultivars maybe had experienced a two-step domestication history. Our results illustrated clear genetic relationships among 380 sweetpotato accessions, exhibiting the potential of accelerating the process of future sweetpotato breeding program by molecular marker based parental selection.

AFLP Fingerprinting and Genetic Diversity of Main Sweetpotato Varieties in China

AFLP fingerprinting of the 98 main sweetpotato varieties planted in China has been constructed. Using 17 AFLP primer combinations which were selected from 1 208 primer combinations and generated the most amounts of polymorphic bands, AFLP analysis of the 98 main sweetpotato varieties gave a total of 410 clear polymorphic bands with an average of 24.12 polymorphic bands per primer combination. Each one of the 98 sweetpotato varieties could be clearly distinguished by EcoR I-cta/Mse I-ggc primer combination which generated the most polymorphic bands. AFLP-based genetic distance ranged from 0.0546 to 0.5709 with an average of 0.3799. The dendrogram based on AFLP markers indicated that sweetpotato varieties coming from the same regions or having same parents were clustered in the same groups. Analysis of molecular variance （AMOVA） revealed greater variations within regions （94.08%） than among regions （5.92%）. Thus, the genetic variations mainly existed within regions, while the variations among regions were very low in the tested sweetpotato varieties. Significant genetic variations existed between ＂Northern＂ and ＂Southern＂ sweetpotato varieties when Yangtze River was used as the dividing line.

Analysis of drought tolerance and genetic and epigenetic variations in a somatic hybrid between Ipomoea batatas (L.) Lam. and I. triloba L.

The somatic hybrid KT1 was previously obtained from protoplast fusion between sweetpotato （Ipomoea batatas （L.） Lam.） cv. Kokei No. 14 and its wild relative I. triloba L. However, its genetic and epigenetic variations have not been investigated. This study showed that KT1 exhibited significantly higher drought tolerance compared to the cultivated parent Kokei No. 14. The content of proline and activities of superoxide dismutase （SOD） and photosynthesis were significantly increased, while malonaldehyde （MDA） content was significantly decreased compared to Kokei No. 14 under drought stress. KT1 also showed higher expression level of well-known drought stress-responsive genes compared to Kokei No. 14 under drought stress. Amplified fragment length polymorphism （AFLP） and methylation-sensitive amplified polymorphism （MSAP） analyses indicated that KT1 had AFLP and MSAP band patterns consisting of both parent specific bands and changed bands. Fur- ther analysis demonstrated that in KT1. the proportions of Kokei No. 14 specific genome components and methylation sites were much greater than those of I. triloba. KT1 had the same chloroplast and mitochondrial genomes as Kokei No. 14. These results will aid in developing the useful genes ofI. triloba and understanding the evolution and phylogeny of the cultivated sweetpotato.

Genetic control of panicle architecture in rice

Rice panicle architecture affects grain number per panicle and thereby grain yield.Many genes involved in control of panicle architecture have been identified in the past decades.According to their effect on phenotype,these genes are divided into three categories:panicle branch and lateral spikelets,multifloret spikelets,and panicle type.We review these genes,describe their genetic regulatory network,and propose a strategy for using them in rice breeding.These findings on rice panicle architecture may facilitate related studies in other crops.

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.

Genetic dissection of carotenoids in maize kernels using high-density single nucleotide polymorphism markers in a recombinant inbred line population

Carotenoids are antioxidants and vitamin A precursors that have important roles in human health. Hence, improving the carotenoid contents in maize kernels is a priority objective for breeders in order to obtain nutritional biofortification outcomes. In the current study, the genetic architecture of carotenoids in maize kernels was explored using a recombinant inbred line(RIL) population derived from a cross between inbred lines By804 and B73. A total of 81 QTLs were detected by using a high-density bin map and a simple sequence repeat(SSR)-based linkage map, with one to seven QTLs for each trait explaining 4.21%–47.53% of the phenotypic variation. A comparison of the QTL mapping efficiency between the two linkage maps revealed that the high-density bin map had higher resolution. In the current study 46 additional QTLs were identified, with 16 being common with previous studies and14 newly identified. Among the results, 29.6%(24/81) of QTLs explained > 10% of the phenotypic variation in the RIL population, and 70.4%(57/81) explained ≤ 10%. These results suggest that a few large-effect QTLs, together with a variable number of minor-effect QTLs,contributed to most of the genetic components of carotenoids in maize kernels.

Comparative genetic mapping revealed powdery mildew resistance gene MlWE4 derived from wild emmer is located in same genomic region of Pm36 and Ml3D232 on chromosome 5BL

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most devastating wheat diseases. Wild emmer wheat（Triticum turgidum ssp. dicoccoides） is a promising source of disease resistance for wheat. A powdery mildew resistance gene conferring resistance to B. graminis f. sp. tritici isolate E09, originating from wild emmer wheat, has been transferred into the hexaploid wheat line WE4 through crossing and backcrossing. Genetic analyses indicated that the powdery mildew resistance was controlled by a single dominant gene, temporarily designated Ml WE4. By mean of comparative genomics and bulked segregant analysis, a genetic linkage map of Ml WE4 was constructed, and Ml WE4 was mapped on the distal region of chromosome arm 5BL. Comparative genetic linkage maps showed that genes Ml WE4, Pm36 and Ml3D232 were co-segregated with markers XBD37670 and XBD37680, indicating they are likely the same gene or alleles in the same locus. The co-segregated markers provide a starting point for chromosome landing and map-based cloning of Ml WE4, Pm36 and Ml3D232.

Genetic diversity and population structure of 288 potato(Solanum tuberosum L.) germplasms revealed by SSR and AFLP markers

Potato （Solanum tuberosum L.） is an important staple food and economic crop in many countries. China has led world potato production in recent years. To understand the genetic diversity of potato germplasms and to enrich the current gene pool for potato improvement, we made a global collection consisted of 288 potato germplasms from eight countries and the International Potato Center （CIP）. Using SSR and AFLP techniques, we evaluated the genetic diversity and population structure of these 288 potato accessions. A total of 190 alleles on 20 SSR loci were detected and all of the SSR alleles were polymorphic among these potato germplasms with an average of 9.5 alleles per SSR locus ranging from 2 to 23. The effective number of alleles per locus （Ne＊）, Nei＇s genetic diversity （H＊）, and Shannon＇s information index （I＊） was from （0.1709＋0.3698） to （1.6166＋0.3414）, （0.076＋0.1388） to （0.3812＋0.1886）, and （0.1324＋0.1970） to （0.5347＋0.1440）, respec- tively, and the mean polymorphic information content （PIC） value was 0.7312. A total of 988 AFLP alleles were detected by 10 AFLP primer combinations with 983 polymorphic alleles, and 99.49% alleles was polymorphic with an average of 98.3 polymorphic alleles per primer combination ranging from 91 to 116. The values of Ne＊, H＊ and/＊ were from （1.5162＋0.311 ） to （1.6423＋0.3278）, （0.3114＋0.145） to （0.3675＋0.1121）, and （0.4761＋0.1792） to （0.547＋0.1322）, respectively, and the average PIC value was 0.9871. Bayesian analysis discriminated the accessions into seven subgroup and an admix group. The majority of accessions from CIP and China were assigned into SG1, SG5, SG6, SG7 and admix group. Accessions in SG3 were mainly from CIP and two small groups SG2 and SG4 were mainly from northeastern China. In general, the results obtained from Bayesian statistical analysis, cluster analysis and principal coordinate analysis consistently revealed the lack of geographical differentiation among country-wide collections, indicating germplasm introduction was common for the countries out of potato origin center. The poiymorphic markers and the differentiate genetic lineages found in this study provide useful information for potato improvement and conservation programs.

Genetic Structure and Eco-Geographical Differentiation of Cultivated Keng Rice(Oryza sativa L.subsp.japonica) in China Revealed by Microsatellites

China is one of the largest centers of genetic diversity of Oryza sativa L. and is the original centers of Oryza sativa L. subspecies japonica. Using a genetically representative core collection of 1 442 rice landraces of japonica in China, the genetic structure, differentiation, and geographic diversity were analyzed. The model-based structure analysis on varieties within three ecotypes revealed 16 eco-geographical types, which are partially accorded with some of the ecological zones in China. The differentiation of eco-geographical types contributed to the local ecological adaption and physical isolation, and maybe could be used to develop the heterotic groups of japonica. To facilitate the identification of different ecotypes and eco-geographical types, we provided the SSR character alleles of each ecotype or geographical eco-group and a rapid discriminated method based on these character alleles. Lastly, investigation on genetic diversity, genetic differentiation indicated that southwest region of China, including south of Yunnan Province, northwest of Guangxi Zhuang Autonomous Region, and southwest of Guizhou Province, possessed the highest genetic diversity and all the necessary conditions as a center of genetic diversity and should be the center of genetic diversity of rice landraces of japonica in China.

Genetic architecture of embryo size and related traits in maize

The embryo in maize has a critical role in controlling kernel nutrition components and grain yield.We measured five embryo weight and size traits,six kernel weight and size traits,and five embryo-tokernel ratio traits in a nested association mapping(NAM)population of 611 recombinant inbred lines(RILs)derived from four inbred lines including the high-oil,giant-embryo line BY815 as the common parent.Using three statistical methods,we identified 5–22 quantitative trait loci(QTL)for each trait,explaining 4.7%–46.7%of the phenotypic variation.The genetic architecture of maize embryo size and its related traits appeared to be dominated by multiple small-effect loci with little epistasis,and the genetic control underlying embryo size appeared to be distinct from that underlying kernel size.A trait–QTL association network included 205 nodes and 439 edges and revealed 28 key loci associated with at least three traits.Cloned maize genes including Zm Urb2,Emp12 and Zm BAM1 d,maize orthologs of known rice genes that control seed size including BG1,XIAO and GS9,and 11 maize orthologs of Arabidopsis EMBRYO-DEFECTIVE(EMB)genes were identified as underlying these key loci.Further,the phenotypic and genetic relationships between embryo size and kernel size were evaluated,and genetic patterns for identified loci that control embryo size and its related traits were proposed.Our findings reveal distinct genetic architectures for embryo size,kernel size,and embryo-to-kernel ratio traits and establish a foundation for the improvement of embryo-size-mediated kernel nutrition and grain yield.

Integrated linkage mapping and genome-wide association study to dissect the genetic basis of zinc deficiency tolerance in maize at seedling stage

Zinc(Zn)deficiency is the most widespread micronutrient deficiency,affecting yield and quality of crops worldwide.Identifying genes associated with Zn-deficiency tolerance in maize is a basis for elucidating its genetic mechanism.A K22×CI7 recombinant inbred population consisting of 210 lines and an association panel of 508 lines were used to identify genetic loci influencing Zn-deficiency tolerance.Under-Zn and-Zn/CK conditions,15 quantitative trait loci(QTL)were detected,each explaining 5.7%-12.6%of phenotypic variation.Sixty-one significant single-nucleotide polymorphisms(SNPs)were identified at P<10^(-5)by genome-wide association study(GWAS),accounting for 5%-14%of phenotypic variation.Among respectively 198 and 183 candidate genes identified within the QTL regions and the 100-kb regions flanking these significant SNPs,12 were associated with Zn-deficiency tolerance.Among these candidate genes,four genes associated with hormone signaling in response to Zn-deficiency stress were co-localized with QTL or SNPs,including the genes involved in the auxin(ZmARF7),and ethylene(ZmETR5,ZmESR14,and ZmEIN2)signaling pathways.Three candidate genes were identified as being responsible for Zn transport,including ZmNAS3 detected by GWAS,ZmVIT and ZmYSL11 detected by QTL mapping.Expression of ZmYSL11 was up-regulated in Zn-deficient shoots.Four candidate genes that displayed different expression patterns in response to Zn deficiency were detected in the regions overlapping peak GWAS signals,and the haplotypes for each candidate gene were further analyzed.

Discrimination of individual seed viability by using the oxygen consumption technique and headspace-gas chromatography-ion mobility spectrometry

Identifying and selecting high-quality seeds is crucial for improving crop yield.The purpose of this study was to improve the selection of crop seeds based on separating vital seeds from dead seeds,by predicting the potential germination ability of each seed,and thus improving seed quality.The methods of oxygen consumption (Q) of seeds and the headspace-gas chromatography-ion mobility spectrometry(HS-GC-IMS) were evaluated for identifying the viability of individual seeds.Firstly,the oxygen consumption technique showed clear differences among the values related to respiratory characteristics for seeds that were either vital or not,and the discrimination ability of final oxygen consumption(Q_(120)) was achieved not only in sweet corn seeds but also in pepper and wheat seeds.Besides,Qtwas established as a new variable to shorten the measuring process in the Q2 (oxygen sensor) procedure,which was significantly related to the viability of individual seeds.To minimize seed damage during measurement,the timing for viability evaluation was pinpointed at the 12,6 and 9 h for pepper,sweet corn,and wheat seeds based on the new variables concerning oxygen consumption (i.e.,Q_(12),Q_(6)and Q_(9),respectively).The accuracies of viability prediction were 91.9,97.7 and 96.2%,respectively.Dead seeds were identified and hence discarded,leading to an enhancement in the quality of the seed lot as indicated by an increase in germination percentage,from 86.6,90.9,and 53.8%to all at 100%.We then used the HS-GC-IMS to determine the viability of individual sweet corn seeds,noting that corn seed has a heavier weight so the volatile gas components are more likely to be detected.A total of 48 chromatographic peaks were identified,among which 38 target compounds were characterized,including alcohols,aldehydes,acids and esters.However,there were no significant differences between the vital and dead seeds,due to the trace amount volatile composition differences among the individual seeds.Furthermore,a PCA based on the signal intensities of the target volatile compounds obtained was found to lose its effectiveness,as it was unable to distinguish those two types of sweet corn seeds.These strategies can provide a reference for the rapid detection of single seed viability.

Fine Mapping and Cloning of the Grain Number Per-Panicle Gene (Gnp4) on Chromosome 4 in Rice (Oryza sativa L.)

Grain number per-panicle is one of the most important components for rice yield. Spikelets on the primary and secondary branches determine the grain number per-panicle in rice. In this study, we identified a natural mutant, gnp4, lack of lateral spikelet on the secondary branches in the field condition. In addition, the Gnp4 and Lax1-1 double mutant showed dramatically reduced secondary branches and spikelets in panicle at reproductive stage, and tillers at vegetative stage. By map-based cloning approach, and using four F2 segregating populations, the Gnp4 gene was finally mapped to a 10.7-kb region on the long arm of chromosome 4 in rice. In this region, only one gene was predicted, and genomic DNA sequencing of the 10.7-kb region showed no nucleotide differences between the mutant and wild type. Interestingly, we found that the methylation level of several cytosines in the promoter CpG islands region of the predicted gene in gnp4 were different from the wild type. Thus, we propose that the DNA methylation changes at these sites may induce to decrease expression level of Gnp4, consequently, resulting in phenotypic variation.

Identification of unconditional and conditional QTL for oil, protein and starch content in maize

Oil, protein and starch are key chemical components of maize kernels. A population of 245 recombinant inbred lines(RILs) derived from a cross between a high-oil inbred line, By804, and a regular inbred line, B73, was used to dissect the genetic interrelationships among oil, starch and protein content at the individual QTL level by unconditional and conditional QTL mapping. Combined phenotypic data over two years with a genetic linkage map constructed using 236 markers, nine, five and eight unconditional QTL were detected for oil, protein and starch content, respectively. Some QTL for oil, protein and starch content were clustered in the same genomic regions and the direction of their effects was consistent with the sign of their correlation. In conditional QTL mapping, 37(29/8) unconditional QTL were not detected or showed reduced effects, four QTL demonstrated similar effects under unconditional and conditional QTL mapping, and 17 additional QTL were identified by conditional QTL mapping. These results imply that there is a strong genetic relationship among oil, protein and starch content in maize kernels. The information generated in the present investigation could be helpful in marker-assisted breeding for maize varieties with desirable kernel quality traits.

SSR fingerprinting of 203 sweetpotato (Ipomoea batatas (L.) Lam.) varieties

Simple sequence repeat （SSR） markers have been shown to be a powerful tool for varieties identification in plants. How- ever, SSR fingerprinting of sweetpotato varieties has been a little reported. In this study, a total of 1 294 SSIR primer pairs, including 1 215 genomic-SSR and 79 expressed sequence tag （EST）-SSR primer pairs, were screened with sweetpotato varieties Zhengshu 20 and Luoxushu 8 and their 2 F1 individuals randomly sampled, and 273 and 38 of them generated polymorphic bands, respectively. Four genomic-SSR and 3 EST-SSR primer pairs, which showed good polymorphism, were selected to amplify 203 sweetpotato varieties and gave a total of 172 bands, 85 （49.42%） of which were polymorphic. All of the 203 sweetpotato varieties showed unique fingerprint patterns, indicating the utility of SSR markers in variety iden- tification of this crop. Polymorphism information content （PIC） ranged from 0.5824 to 0.9322 with an average of 0.8176. SSR-based genetic distances varied from 0.0118 to 0.6353 with an average of 0.3100 among these varieties. Thus, these sweetpotato varieties exhibited high levels of genetic similarity and had distinct fingerprint profiles. The SSR fingerprints of the 203 sweetpotato varieties have been successfully constructed. The highly polymorphic SSR primer pairs developed in this study have the potential to be used as core primer pairs for variety identification, genetic diversity assessment and linkage map construction in sweetpotato and other plants.

Molecular Cloning and Functional Characterization of a Salt Tolerance-Associated Gene IbNFU1 from Sweetpotato

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.Based on the EST sequence selected from salt-stressed suppression subtractive hybridization（SSH） cDNA library constructed with a salt-tolerant mutant LM79,a NFU gene,termed IbNFU1,was cloned from sweetpotato（Ipomoea batatas（L.） Lam.） via rapid amplification of cDNA ends（RACE）.The cDNA sequence of 1 117 bp contained an 846 bp open reading frame encoding a 281 amino acids polypeptide with a molecular weight of 30.5 kDa and an isoelectric point（pI） of 5.12.IbNFU1 gene contained a conserved Cys-X-X-Cys motif in C-terminal of the iron-sulfur cluster domain.The deduced amino acid sequence had 66.08 to 71.99% sequence identity to NFU genes reported in Arabidopsis thaliana,Eucalyptus grandis and Vitis vinifera.Real-time quantitative PCR analysis revealed that the expression level of IbNFU1 gene was significantly higher in the roots of the mutant LM79 compared to the wild-type Lizixiang.Transgenic tobacco（cv.Wisconsin 38） plants expressing IbNFU1 gene exhibited significantly higher salt tolerance compared to the untransformed control plants.It is proposed that IbNFU1 gene has an important function for salt tolerance of plants.