Biology subjects

Jaiwar, S.

Publications and source records attributed to Jaiwar, S..

3 recordsLinked to original sources

bioRxiv2022

Long-read genome sequencing accelerated the cloning of Pm69 by resolving the complexity of a rapidly evolving resistance gene cluster in wheat

Gene cloning in repeat-rich polyploid genomes remains challenging. Here we describe a strategy for overcoming major bottlenecks in the cloning of the powdery mildew (Pm) resistance gene (R-gene) Pm69 derived from tetraploid wild emmer wheat (WEW). A conventional positional cloning approach encountered suppressed recombination due to structural variations, while chromosome sorting yielded an insufficient purity level. A Pm69 physical map, constructed by assembling ONT long-read genome sequences, revealed a rapidly evolving nucleotide-binding leucine-rich repeat (NLR) R-gene cluster. A single candidate NLR was identified within this cluster by anchoring RNASeq reads of susceptible mutants to ONT contigs and was validated by the virus-induced gene silencing (VIGS) approach. Pm69, comprising Rx_N with RanGAP interaction sites, NB-ARC, and LRR domains, is probably a newly evolved NLR discovered only in one location across the WEW distribution range in the Fertile Crescent. Pm69 was successfully introgressed into durum and bread wheat, and a diagnostic molecular marker could be used to accelerate its deployment and pyramiding with other resistance genes.

genetics↗

bioRxiv2022

Intracellular reactive oxygen species (intraROS)-aided localized cell death contributing to immune responses against wheat powdery mildew pathogen

Reactive oxygen species (ROS) and hypersensitive response (HR) mediated cell death have long been known to play critical roles in plant immunity to pathogens. Wheat powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a destructive wheat pathogen. Here, we report a quantitative analysis of the proportion of infected cells with local apoplastic ROS (apoROS) versus intracellular ROS (intraROS) accumulation in various wheat accessions that carry different disease resistance genes (R genes), at a series of time points post-infection. The proportion of apoROS accumulation was 70-80% of the infected wheat cells detected in both compatible and incompatible host-pathogen interactions. However, intensive intraROS accumulation followed by localized cell death responses were detected in 11-15% of the infected wheat cells, mainly in wheat lines that carried nucleotide-binding leucine-rich repeat (NLR) R genes (e.g. Pm3F, Pm41, TdPm60, MIIW72, Pm69). The lines that carry unconventional R genes, Pm24 (Wheat Tandem Kinase 3) and pm42 (a recessive R gene), showed very less intraROS responses, while 11% of Pm24 line infected epidermis cells still showed HR cell death, suggesting that different resistance pathways are activated there. Here, we also demonstrated that ROS could not act as a strong systemic signal for inducing high resistance to Bgt in wheat, although it induced the expression of pathogenesis-related (PR) genes. These results provide new insights on the contribution of intraROS and localized cell death to immune responses against wheat powdery mildew.

pathology↗

bioRxiv2020

Three previously characterized resistances to yellow rust are encoded by a single locus Wtk1

The wild emmer wheat (Triticum turgidum ssp. dicoccoides; WEW) yellow (stripe) rust resistance genes Yr15, YrG303 and YrH52 were discovered in natural populations from different geographic locations. They all localize to chromosome 1B but were thought to be non-allelic based on differences in resistance response. We recently cloned Yr15 as a Wheat Tandem Kinase 1 (WTK1) and showed here that these three resistance loci co-segregate in fine-mapping populations and share identical full-length genomic sequence of functional Wtk1. Independent EMS mutagenized susceptible yrG303 and yrH52 lines carried single nucleotide mutations in Wtk1 that disrupted function. A comparison of the mutations for yr15, yrG303 and yrH52 mutants showed that while key conserved residues were intact, other conserved regions in critical kinase subdomains were frequently affected. Thus, we concluded that Yr15-, YrG303- and YrH52-mediated resistances to yellow rust are encoded by a single locus Wtk1. Introgression of Wtk1 into multiple genetic backgrounds resulted in variable phenotypic responses, confirming that Wtk1-mediated resistance is part of a complex immune response network. WEW natural populations subjected to natural selection and adaptation have potential to serve as a good source for evolutionary studies of different traits and multifaceted gene networks. HighlightWe demonstrate that Yr15, YrG303 and YrH52 resistances are encoded by the Wtk1 locus, but express variable resistance responses to yellow rust in a genetic background dependent manner.

genetics↗