Identification and fine mapping of qSW2 for leaf slow wilting in soybean

Drought is one of the abiotic stresses limiting the production of soybean(Glycine max).Elucidation of the genetic and molecular basis of the slow-wilting(SW)trait of this crop offers the prospect of its genetic improvement.A panel of 188 accessions and a set of recombinant inbred lines produced from a cross between cultivars Liaodou 14 and Liaodou 21 were used to identify quantitative-trait loci(QTL)associated with SW.Plants were genotyped by Specific-locus amplified fragment sequencing and seedling leaf wilting was assessed under three water-stress treatments.A genome-wide association study identified 26 SW-associated single-nucleotide polymorphisms(SNPs),including three located in a 248-kb linkage-disequilibrium(LD)block on chromosome 2.Linkage mapping revealed a major-effect QTL,qSW2,associated with all three treatments and adjacent to the LD block.Fine mapping in a BC_(2)F_(3) population derived from a backcross between Liaodou 21 and R26 confined qSW2 to a 60-kb interval.Gene expression and sequence variation analysis identified the gene Glyma.02 g218100,encoding an auxin transcription factor,as a candidate gene for qSW2.Our results will contribute significantly to improving drought-resistant soybean cultivars by providing genetic information and resources.

The transcription factor ZmNAC84 increases maize salt tolerance by regulating ZmCAT1 expression

Salt stress severely affects plant growth and yield.The transcription factor NAC plays a variety of important roles in plant abiotic stress,but we know relatively little about the specific molecular mechanisms of NAC in antioxidant defense.Here,our genetic studies reveal the positive regulation of salt tolerance in maize by the transcription factor ZmNAC84.Under salt stress,overexpression of ZmNAC84 in maize increased the expression of ZmCAT1,enhanced CAT activity,and consequently reduced H_(2)O_(2) accumulation,thereby improving salt stress tolerance in maize.Whereas RNA interference-mediated knockdown of ZmNAC84 produced the opposite effect.Subsequently,we found that ZmNAC84 directly binds to and regulates the expression of the ZmCAT1 promoter,and the hybridized material also demonstrated that ZmCAT1 is a downstream target gene of ZmNAC84.In addition,phenotypic and biochemical analyses indicated that ZmCAT1 positively regulated salt tolerance by regulating H_(2)O_(2) accumulation under salt stress.Taken together,these results reveal the function of ZmNAC84 in regulating ZmCAT1-mediated antioxidant defense in response to salt stress in plants.

Effects of potassium deficiency on photosynthesis and photoprotection mechanisms in soybean(Glycine max(L.)Merr.)

Potassium is an important nutrient element requiring high concentration for photosynthetic metabolism.The potassium deficiency in soil could inhibit soybean（Glycine max（L.） Merr.） photosynthesis and result in yield reduction.Research on the photosynthetic variations of the different tolerant soyben varieties should provide important information for high yield tolerant soybean breeding program.Two representative soybean varieties Tiefeng 40（tolerance to K^＋ deficiency） and GD8521（sensitive to K^＋ deficiency） were hydroponically grown to measure the photosynthesis,chlorophyll fluorescence parameters and Rubisco activity under different potassium conditions.With the K-deficiency stress time extending,the net photosynthetic rate（Pn）,transpiration rate（Tr） and stomatal conductance（Gs） of GD8521 were significantly decreased under K-deficiency condition,whereas the intercellular CO2 concentration（Ci） was significantly increased.As a contrast,the variations of Tiefeng 40 were almost little under K-deficiency condition,which indicated tolerance to K^＋ deficiency variety could maintain higher efficient photosynthesis.On the 25 th d after treatment,the minimal fluorescence（F0） of GD8521 was significantly increased and the maximal fluorescence（Fm）,the maximum quantum efficiency of PSII photochemistry（F√Fm）,actual photochemical efficiency of PSII（φ（PSII））,photochemical quenching（qp）,and electron transport rate of PSII（ETR）were significantly decreased under K^＋ deficiency condition.In addition,the Rubisco content of GD8521 was significantly decreased in leaves.It is particularly noteworthy that the chlorophyll fluorescence parameters and Rubisco content of Tiefeng 40 were unaffected under K^＋ deficiency condition.On the other hand,the non-photochemical quenching（qN） of Tiefeng 40 was significantly increased.The dry matter weight of Tiefeng 40 was little affected under K^＋ deficiency condition.Results indicated that Tiefeng 40 could avoid or relieve the destruction of PSII caused by exceeded absorbed solar energy under K-deficiency condition and maintain natural photosynthesis and plant growth.It was an essential physiological mechanism for low-K-tolerant soybean under K-deficiency stress.

Genetic analysis of fertility restoring genes for AL-type male sterility in wheat

In order to screen molecular markers linked to fertility restoring genes and further improve the breeding efficiency of restorer lines, in this study, wheat varieties 18A, 18B and 99AR144-1 were used as experimental materials to establish F2 fertility-segregating population. Plant quantitative trait ＂major gene ＋ polygene mixed mo- del＂ separation analysis method and simple sequence repeat （SSR） molecular markers were adopted for genetic analysis of four generations, including the parents （P~ and P2）, and hybrid （G and G） populations. The results show that AL-type fertility restoring gene is controlled by two pairs of additive-dominant-epistatic genes and addi- tive-dominant polygene; two primers linked to fertility restoring genes were selected by SSR molecular markers, including Xgwm95 on chromosome 2A and Barc61 on chromosome 1B, with the linkage distance of 15.0 cM and 18.0 cM, respectively. Based on verification, these two markers are reliable for distinguishing AL-type wheat ste- rile lines and restorer lines.

Identification of Resistance of Powdery Mildew and Stripe Rust of Winter Wheat Strains in Xinjiang

Wheat powdery mildew and stripe rust are the major diseases in wheat producing area in Xinjiang.To obtain wheat germplasm resources and varieties resistant to powdery mildew and rust,36 high-generation stable strains of Xinjiang winter wheat were evaluated using the method of natural inducement from 2018 to 2020.A total of 5 strains with high resistance to powdery mildew,4 strains with slow stripe rust and 1 strain with resistance to powdery mildew and adult plant slow stripe rust were obtained.And the parental combination of disease-resistant varieties was analyzed.These studies will provide theoretical basis for the breeding of resistant wheat varieties in Xinjiang.

Wheat breeding in northern China: Achievements and technical advances

Common wheat is the major cereal crop that underpins the food safety of China. Both winter wheat and spring wheat are grown on ~24 million ha. This review aims to summarize the current status of wheat production and breeding progress in the northern wheat production areas of the country, and to review recently advanced technologies being applied in wheat breeding, including the use of dwarf-male-sterile(DMS) wheat, speed breeding and specialized wheat breeding SNP chips. Crossing is the initial step in most breeding programs. DMS wheat is a convenient tool for large scale production of hybrid seed. Speed breeding or accelerated generation turnover attempts to reduce the time taken in cultivar development. Several different SNP chips are high-throughput, genome-wide genotyping platforms for breeding and research.

DNA repair-and nucleotide metabolism-related genes exhibit differential CHG methylation patterns in natural and synthetic polyploids (Brassica napus L.)

Polyploidization plays a crucial role in the evolution of angiosperm species.Almost all newly formed polyploids encounter genetic or epigenetic instabilities.However,the molecular mechanisms contributing to genomic instability in synthetic polyploids have not been clearly elucidated.Here,we performed a comprehensive transcriptomic and methylomic analysis of natural and synthetic polyploid rapeseeds(Brassica napus).Our results showed that the CHG methylation levels of synthetic rapeseed in different genomic contexts(genes,transposon regions,and repeat regions)were signi fi cantly lower than those of natural rapeseed.The total number and length of CHG-DMRs between natural and synthetic polyploids were much greater than those of CG-DMRs and CHH-DMRs,and the genes overlapping with these CHG-DMRs were signi fi cantly enriched in DNA damage repair and nucleotide metabolism pathways.These results indicated that CHG methylation may be more sensitive than CG and CHH methylation in regulating the stability of the polyploid genome of B.napus.In addition,many genes involved in DNA damage repair,nucleotide metabolism,and cell cycle control were significantly differentially expressed between natural and synthetic rapeseeds.Our results highlight that the genes related to DNA repair and nucleotide metabolism display differential CHG methylation patterns between natural and synthetic polyploids and reveal the potential connection between the genomic instability of polyploid plants with DNA methylation defects and dysregulation of the DNA repair system.In addition,it was found that the maintenance of CHG methylation in B.napus might be partially regulated by MET1.Our study provides novel insights into the establishment and evolution of polyploid plants and offers a potentialidea for improving the genomic stability of newly formed Brassica polyploids.

Characterization of a PDR type ABC transporter gene from wheat (Triticum aestivum L.)

DON, as a virulence factor, plays an important role in the infection of Fusarium graminearum in wheat. The infection ability of F. graminearum depends on its capacity of producing DON. The production of DON by F. graminearum is significantly decreased in the wheat varieties with scab resistance. In this study, GeneChip analysis indicated that an EST encoding an ATP-binding cassette (ABC) transporter was up-regulated by 45 times in a wheat landrace Wangshuibai, which is resistant to DON accumulation. A pair of EST-derived primers were designed based on the EST sequence, and a clone was then isolated from a wheat genomic DNA TAC library. The TAC clone was sequenced using chromosome walking and gene prediction was conducted using Softberry. A cDNA clone of this gene was subsequently isolated from Wangshuibai induced by DON using gene-specific primers designed according to the untranslated sequence of the gene. The genome size of the gene is 7377 bp, consisting of 19 exons with coding sequences of 4308 bp. It encodes a protein with 1435 amino acid residues and the calculated molecular weight is about 161 kD. BLAST analysis indicated that the gene may belong to pleiotropic drug resistance (PDR) sub-family, and hence designated as TaPDR1 (Triticum aestivum pleiotropic drug resistance). TaPDR1 was located on chromosome 5A of wheat using nullisomic-tetrasomic lines of Chinese Spring. TaPDR1 was up-regulated by induction of both DON and F. graminearum. Expression patterns of TaPDR1 were different in wild-type Wangshuibai and the fast-neutron induced Wangshuibai mutant lacking FHB1, a major QTL of FHB resistance and DON resistance in chromosome arm 3BS. These results suggested that TaPDR1 might be a candidate gene responsible for DON ac-cumulation resistance. The expression profile showed that TaPDR1 expression was neither induced by hormones typically involved in biotic stress, such as JA and SA, nor by abiotic stresses, such as heat, cold, wounding and NaCl. However, TaPDR1 expression was regulated by Al3+ and [Ca2+], indicating that [Ca2+]i might mediate the signal of TaPDR1 expression.

Wheat genomic study for genetic improvement of traits in China

Bread wheat(Triticum aestivum L.)is a major crop that feeds 40%of the world’s population.Over the past several decades,advances in genomics have led to tremendous achievements in understanding the origin and domestication of wheat,and the genetic basis of agronomically important traits,which promote the breeding of elite varieties.In this review,we focus on progress that has been made in genomic research and genetic improvement of traits such as grain yield,end-use traits,flowering regulation,nutrient use efficiency,and biotic and abiotic stress responses,and various breeding strategies that contributed mainly by Chinese scientists.Functional genomic research in wheat is entering a new era with the availability of multiple reference wheat genome assemblies and the development of cutting-edge technologies such as precise genome editing tools,highthroughput phenotyping platforms,sequencing-based cloning strategies,high-efficiency genetic transformation systems,and speed-breeding facilities.These insights will further extend our understanding of the molecular mechanisms and regulatory networks underlying agronomic traits and facilitate the breeding process,ultimately contributing to more sustainable agriculture in China and throughout the world.

Genomic insights on the contribution of introgressions from Xian/Indica to the genetic improvement of Geng/Japonica rice cultivars

Hybridization between Xian/indica(XI)and Geng/japonica(GJ)rice combined with utilization of plant ideotypes has greatly contributed to yield improvements in modern GJ rice in China over the past 50 years.To explore the genomic basis of improved yield and disease resistance in GJ rice,we conducted a large-scale genomic landscape analysis of 816 elite GJ cultivars representing multiple eras of germplasm from China.We detected consistently increasing introgressions from three XI subpopulations into GJ cultivars since the 1980s and found that the XI genome introgressions significantly increased the grain number per panicle(GN)and decreased the panicle number per plant.This contributed to the improvement of plant type during modern breeding,changing multi-tiller plants tomoderate tiller plants with a large panicle size and increasing the blast resistance.Notably,we found that key gene haplotypes controlling plant architecture,yield components,and pest and disease resistance,including IPA1,SMG1,DEP3,Pib,Pi-d2,and Bph3,were introduced from XI rice by introgression.By GWAS analysis,we detected a GN-related gene Gnd5,which had been consistently introgressed from XI into GJ cultivars since the 1980s.Gnd5 is a GRAS transcription factor gene,and Gnd5 knockout mutants showed a significant reduction in GN.The estimated genetic effects of genes varied among different breeding locations,which explained the distinct introgression levels of XI gene haplotypes,including Gnd5,DEP3,etc.,to these GJ breeding pedigrees.These findings reveal the genomic contributions of introgressions from XI to the trait improvements of GJ rice cultivars and provide new insights for future rice genomic breeding.

A conserved unusual posttranscriptional processing mediated by short,direct repeated (SDR) sequences in plants

In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and 3＇ splicing junctions that are distinct from conventional （U2/U12-type） splicing boundaries.By using the known SDR-containing sequences as probes,24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database.The SDRs-mediated posttranscriptional processing events including cis-and trans-actions were experimentally detected in majority of the predicted candidates.Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion,exon fragment repetition,exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules.In addition,we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems.We also show prokaryote is incapable of SDR-mediated premRNA splicing.