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Avirulence depletion assay: Combining R gene-mediated selection with bulk sequencing for rapid avirulence gene identification in wheat powdery mildew.

Wheat production is threatened by multiple fungal pathogens, such as the wheat powdery mildew fungus (Blumeria graminis f. sp. tritici, Bgt). Wheat resistance breeding frequently relies on the use of resistance (R) genes that encode diverse immune receptors which detect specific avirulence (AVR) effectors and subsequently induce an immune response. While R gene cloning has accelerated recently, AVR identification in many pathogens including Bgt lags behind, preventing pathogen-informed deployment of resistance sources. Here we describe a new "avirulence depletion (AD) assay" for rapid identification of AVR genes in Bgt. This assay relies on the selection of a segregating, haploid F1 progeny population on a resistant host, followed by bulk sequencing, thereby allowing rapid avirulence candidate gene identification with high mapping resolution. In a proof-of-concept experiment we mapped the AVR component of the wheat immune receptor Pm3a to a 25 kb genomic interval in Bgt harboring a single effector, the previously described AvrPm3a2/f2. Subsequently, we applied the AD assay to map the unknown AVR effector recognized by the Pm60 immune receptor. We show that AvrPm60 is encoded by three tandemly arrayed, nearly identical effector genes that trigger an immune response upon co-expression with Pm60 and its alleles Pm60a and Pm60b. We furthermore provide evidence that Pm60 outperforms Pm60a and Pm60b through more efficient recognition of AvrPm60 effectors, suggesting it should be prioritized for wheat breeding. Finally, we show that virulence towards Pm60 is caused by simultaneous deletion of all AvrPm60 gene paralogs and that isolates lacking AvrPm60 are especially prevalent in the US thereby limiting the potential of Pm60 in this region. The AD assay is a powerful new tool for rapid and inexpensive AVR identification in Bgt with the potential to contribute to pathogen-informed breeding decisions for the use of novel R genes and regionally tailored gene deployment.

Triticum

Integrated Genomics and Transcriptomics Reveal Stable Resistance Loci and Candidate Genes for Powdery Mildew in Wheat.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), poses a substantial threat to global wheat production. Enhancing resistance through molecular breeding necessitates a comprehensive understanding of its genetic and molecular underpinnings. This study leveraged a 2-year phenotypic evaluation of 283 diverse wheat accessions combined with genome-wide association studies (GWAS) to pinpoint stable quantitative trait loci for powdery mildew resistance. We identified 52 robust resistance loci across the wheat genome, including seven novel loci consistently detected across four environments. Comparative transcriptome profiling of resistant and susceptible wheat lines revealed 95 differentially expressed genes, predominantly enriched in defense response, signal transduction, and transcription regulation pathways. By integrating the GWAS and transcriptomic data, we precisely identified three compelling candidate genes (TaPIP5K, TaPKG, and TaORR6) on chromosome 2A, which are implicated in cell wall reinforcement, jasmonic acid signaling, and reactive oxygen species scavenging, respectively. Further validation using expression analysis corroborated their pivotal roles in resistance. Our findings provide a rich repository of validated genetic markers, promising candidate genes, and superior resistant germplasms, offering critical resources to accelerate targeted molecular breeding efforts for durable powdery mildew resistance in wheat.

Blumeria graminis f. sp. tritici

Novel genomic regions associated with adult-plant resistance to multiple fungal pathogens in wheat (Triticum aestivum L.) revealed by DArT marker sequencing.

Wheat is among the top three most important cereal crops globally and serves as a staple food for approximately 40% of the world's population. Fungal leaf diseases such as yellow and leaf rusts (YR, LR), septoria nodorum blotch (SNB), septoria tritici blotch (STB), and powdery mildew (PM) have a major effect on yield loss in wheat, and resistance breeding is so far the most effective strategy to minimize those losses. Adult plant resistance (APR) is a crucial component of durable disease resistance; it reduces the pathogen's infection rate, keeping disease levels below the damage threshold, even in the absence of complete immunity. Therefore, this study aimed to identify sources of resistance in a collection of 411 accessions from diverse global origins. These accessions were phenotyped across 2018-2019. DArTseq technology and Genome-wide association studies (GWAS) analysis were conducted to identify single-nucleotide polymorphisms (SNPs) associated with APR for evaluated pathogens. DArT analysis showed that wheat chromosome 2B contains genomic regions associated with resistance to SNB, and that SNPs on chromosome 3B are associated with resistance to YR. On chromosome 6 A, there is a strong potential to explore, as a shared resistance locus for YR and SNB was found. SNPs: 3,937,236, 1,056,817 were consistent in both years, meaning their association with disease resistance is reliable and repeatable. Chromosome 7D is a strong region for SNPs significantly associated with both LR and SNB resistance. While multiple disease resistance genes are present on 7D, the 610 Mb LR locus is distinct from known LR, PM, and SNB loci, making it a strong candidate for functional validation. These findings highlight the value of historical resistance sources and uncover novel genomic regions for breeding a broad-spectrum APR-based resistance. Dual-trait loci, especially those effective against both biotrophic and necrotrophic pathogens, represent a promising material for achieving durable resistance in elite wheat cultivars.

Triticum

Phylogenetic and Functional Analyses of Wheat TaMAN Genes Responding to Salinity and Pathogens.

Endo-β-1,4-mannanases (MANs) are glycoside hydrolase family 5 (GH5) enzymes that degrade cell wall mannan polysaccharides and participate in plant growth and stress adaptation. This gene family has not been systematically characterized in common wheat (Triticum aestivum L.). Here, we identified 24 TaMAN genes (TaMAN1-TaMAN24) genome-wide and analyzed their phylogeny, gene structures, chromosomal distribution, synteny, and promoter cis-acting elements. Expression profiles under biotic and abiotic stresses were investigated using public databases, salt-stress RNA-seq, and RT-qPCR. TaMAN proteins (386-475 aa) were mainly predicted to localize in the extracellular space. Phylogenetic analysis divided them into three groups, with Groups II and III representing monocot-specific expansions. Family expansion was driven primarily by whole-genome duplication, supplemented by tandem duplication on homoeologous group 6. Promoters were enriched in hormone- and stress-responsive cis-acting elements (ABRE, as-1/CGTCA-motif, W box). TaMAN1, TaMAN5, TaMAN8, TaMAN9, TaMAN16 and TaMAN19 were significantly induced by powdery mildew, while TaMAN3, TaMAN4 and TaMAN19-TaMAN22 rapidly responded to salt stress. This study provides candidate genes for disease-resistant and salt-tolerant wheat breeding.

TaMAN gene