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Spot blotch (SB) is a major constraint to wheat (Triticum aestivum L.) production in South Asia's warmer plains. SB, also known as leaf blight, is caused by Bipolaris sorokiniana and causes significant yield losses in India's Eastern Gangetic Plain Zone. The aim of this study was to map SB resistance via composite interval mapping (CIM) in the PBW343/IC252874 population, which comprised of 165 doubled haploid lines (DHLs), across two years in India. The phenotypic analysis of these lines revealed a constant variance in disease severity, implying that SB resistance is most likely polygenic. DHLs' phenotypic data was also used to map QTLs using SSR markers. The presence of quantitative inheritance with transgressive segregation for SB resistance in the population was also revealed. The QTLs were discovered on 12 chromosomes i.e. 1B, 1D, 2A, 2B, 2D, 3B, 4A, 4D, 5A, 5B, 6A, and 7A. A new QTL was detected on chromosome 4D being linked to SB in both years. We have also found two consistent QTLs on the chromosomes, 2B and 5B with the average PVE of 17.9% and 19.9% respectively. These findings reveal new genomic areas linked to spot blotch disease, which could be used in disease resistance breeding strategies in wheat advancement with further validation.

Twenty-one quantitative trait loci were discovered across six environments, including three (NS), seven (LS), and eleven (VLS) conditions. The linkage groups 1A, 1B, 2A, 2B, 2D, 3B, 4A, 6A, 6B, and 7D spanned QTLs. For CT, a stable QTL (Qct_rpcau_4A) in the environment E6 has shown a PVE up to 17.85%. The QTL, Qspad_rpcau_2D was found to be stable for SPAD value, explaining the PVE of 15.05%.Whereas, three stable QTLs viz. Qgy_rpcau_3B, Qgy_rpcau_4A and Qgy_rpcau_6A were associated with the chromosomes 3B, 4A and 6B explaining a PVE of 20.85%, 17.43% and 17.37% respectively for the trait GY. The interaction of genotype and environment has been shown to be useful in determining the best lines for heat stressed environments. In addition, G X E analysis was performed on the population. In the ranking of genotypes for both mean yield and mean Vs. stability, GGE biplot across the six environments, DH 146, 195, 60, 202, 65, 155, 124, 5, 201, 169, 15, and 170 were ranked closest to ideal and winning genotype; these were highly adapted and most stable lines. The goal of the current investigation was to find the best suitable double haploid lines which can withstand heat-stress and to find those QTLs which are influential to heat stress for the studied traits.

Auxin is an important phytohormone that regulates response, differentiation, and development of plant cell, tissue, and organs. Along with its local production, long-distance transport coordinated by the efflux/influx membrane transporters is instrumental in plant development and architecture. In the present study, we cloned and characterized a wheat (Triticum aestivum) auxin efflux carrier ABCB1. The TaABCB1 was physically localized to the proximal 15% of the short arm of wheat homoeologous group 7 chromosomes. Size of the Chinese spring (CS) homoeologs genomic copies ranged from 5.3–6.2 kb with the 7A copy being the largest due to novel insertions in its third intron. The three homoeologous copies share 95–97% sequence similarity at the nucleotide, 98–99% amino acid, and overall Q-score of 0.98 at 3-D structure level. Though detected in all analyzed tissues, TaABCB1 predominantly expressed in the meristematic tissues likely due to the presence of meristem-specific activation regulatory element identified in the promoter region. RNAi plants of TaABCB1 gene resulted in reduced plant height and increased seed width. Promoter analysis revealed several responsive elements detected in the promoter region including that for different hormones as auxin, gibberellic acid, jasmonic acid and abscisic acid, light, and circadian regulated elements.

The elevating temperature makes heat stress one of the major issues for wheat production globally. To elucidate genetic basis and map heat tolerance traits, a set of 166 doubled haploid lines (DHLs) derived from the cross between PBW3438/IC252874 was used. The population was evaluated under Normal sown (NS) and late sown (LS) conditions, by exposing to heat stress during rabi season. The canopy temperature (CT) showed positive correlations with grain yield, whereas Soil plant analysis development (SPAD) was not significantly correlated and associated with GY in both the normal and late sown conditions. Composite interval mapping (CIM) identified total 12 Quantitative trait loci (QTLs) viz., 2 (Normal sown), 10 (late sown) mapped on linkage groups 1A, 1D, 2B, 2D, 3B, 4D, 5B and 6D, during both the crop seasons 2017-18 and 2018-19. Combining the results of these QTLs revealed a major stable QTL for grain yield (GY) on chromosome 3B with 11.84% to 21.24% explaining phenotypic variance under both sowing conditions. QTL for CT and SPAD was detected on chromosome 1A while QTL for GY on chromosome 3B and 5B. The identified QTLs in the genomic regions could be targeted for genetic improvement and marker assisted selection for heat tolerance in wheat. The tools like SPAD and CT could be exploited to screen the large number of breeding lines.

To improve the efficiency of high-density genotype data storage and imputation in bread wheat (Triticum aestivum L.), we applied the Practical Haplotype Graph (PHG) tool. The Wheat PHG database was built using whole-exome capture sequencing data from a diverse set of 65 wheat accessions. Population haplotypes were inferred for the reference genome intervals defined by the boundaries of the high-quality gene models. Missing genotypes in the inference panels, composed of wheat cultivars or recombinant inbred lines genotyped by exome capture, genotyping-by-sequencing (GBS), or whole-genome skim-seq sequencing approaches, were imputed using the Wheat PHG database. Though imputation accuracy varied depending on the method of sequencing and coverage depth, we found 92% imputation accuracy with 0.01× sequence coverage, which was slightly lower than the accuracy obtained using the 0.5× sequence coverage (96.6%). Compared to Beagle, on average, PHG imputation was ∼3.5% (P-value < 2 × 10−14) more accurate, and showed 27% higher accuracy at imputing a rare haplotype introgressed from a wild relative into wheat. We found reduced accuracy of imputation with independent 2× GBS data (88.6%), which increases to 89.2% with the inclusion of parental haplotypes in the database. The accuracy reduction with GBS is likely associated with the small overlap between GBS markers and the exome capture dataset, which was used for constructing PHG. The highest imputation accuracy was obtained with exome capture for the wheat D genome, which also showed the highest levels of linkage disequilibrium and proportion of identity-by-descent regions among accessions in the PHG database. We demonstrate that genetic mapping based on genotypes imputed using PHG identifies SNPs with a broader range of effect sizes that together explain a higher proportion of genetic variance for heading date and meiotic crossover rate compared to previous studies.

Vernalization genes underlying dramatic differences in flowering time between spring wheat and winter wheat have been studied extensively, but little is known about genes that regulate subtler differences in flowering time among winter wheat cultivars, which account for approximately 75% of wheat grown worldwide. Here, we identify a gene encoding an O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) that differentiates heading date between winter wheat cultivars Duster and Billings. We clone this TaOGT1 gene from a quantitative trait locus (QTL) for heading date in a mapping population derived from these two bread wheat cultivars and analyzed in various environments. Transgenic complementation analysis shows that constitutive overexpression of TaOGT1b from Billings accelerates the heading of transgenic Duster plants. TaOGT1 is able to transfer an O-GlcNAc group to wheat protein TaGRP2. Our findings establish important roles for TaOGT1 in winter wheat in adaptation to global warming in the future climate scenarios., Little is known about genes that regulate flowering time difference among winter wheat cultivars. Here, via map-based cloning, the authors show the role of an O-linked N-acetylglucosamine (O-GlcNAc) transferase TaOGT1 in regulating flowering time difference among winter wheat cultivars.

Programmed cell death (PCD) and apoptosis have key functions in development and disease resistance in diverse organisms; however, the induction of necrosis remains poorly understood. Here, we identified a semi-dominant mutant allele that causes the necrotic death of the entire seedling (DES) of wheat (Triticum aestivum L.) in the absence of any pathogen or external stimulus. Positional cloning of the lethal allele mDES1 revealed that this premature death via necrosis was caused by a point mutation from Asp to Asn at amino acid 441 in a nucleotide-binding leucine-rich repeat protein containing nucleotide-binding domain and leucine-rich repeats. The overexpression of mDES1 triggered necrosis and PCD in transgenic plants. However, transgenic wheat harboring truncated wild-type DES1 proteins produced through gene editing that exhibited no significant developmental defects. The point mutation in mDES1 did not cause changes in this protein in the oligomeric state, but mDES1 failed to interact with replication protein A leading to abnormal mitotic cell division. DES1 is an ortholog of Sr35, which recognizes a Puccinia graminis f. sp. tritici stem rust disease effector in wheat, but mDES1 gained function as a direct inducer of plant death. These findings shed light on the intersection of necrosis, apoptosis, and autoimmunity in plants.

Heat Shock Protein 101 (HSP101), the homolog of Caseinolytic Protease B (CLPB) proteins, has functional conservation across species to play roles in heat acclimation and plant development. In wheat, several TaHSP101/CLPB genes were identified, but have not been comprehensively characterized. Given the complexity of a polyploid genome with its phenomena of homoeologous expression bias, detailed analysis on the whole TaCLPB family members is important to understand the genetic basis of heat tolerance in hexaploid wheat. In this study, a genome-wide analysis revealed thirteen members of TaCLPB gene family and their expression patterns in various tissues, developmental stages, and stress conditions. Detailed characterization of TaCLPB gene and protein structures suggested potential variations of the sub-cellular localization and their functional regulations. We revealed homoeologous specific variations among TaCLPB gene copies that have not been reported earlier. A study of the Chromosome 1 TaCLPB in four wheat genotypes demonstrated unique patterns of the homoeologous gene expression under moderate and extreme heat treatments. The results give insight into the strategies to improve heat tolerance by targeting one or some of the TaCLPB genes in wheat.

Although studied extensively since 1958, the molecular mode of action of the Pairing homeologous 1 (Ph1) gene is still unknown. In polyploid wheat, the diploid-like chromosome pairing is principally controlled by the Ph1 gene via preventing homeologous chromosome pairing (HECP). Here, we report a candidate Ph1 gene (C-Ph1) present in the Ph1 locus, transient as well as stable silencing of which resulted in a phenotype characteristic of the Ph1 gene mutants, including HECP, multivalent formation, and disrupted chromosome alignment on the metaphase I (MI) plate. Despite a highly conserved DNA sequence, the C-Ph1 gene homeologues showed a dramatically different structure and expression pattern, with only the 5B copy showing MI-specific expression, further supporting our claim for the Ph1 gene. In agreement with the previous reports about the Ph1 gene, the predicted protein of the 5A copy of the C-Ph1 gene is truncated, and thus perhaps less effective. The 5D copy is expressed around the onset of meiosis; thus, it may function during the earlier stages of chromosome pairing. Along with alternate splicing, the predicted protein of the 5B copy is different from the protein of the other two copies because of an insertion. These structural and expression differences among the homeologues concurred with the previous observations about Ph1 gene function. Stable RNAi silencing of the wheat gene in Arabidopsis showed multivalents and centromere clustering during meiosis I.