ORCID Profile
0000-0002-4888-7216
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Publisher: Springer Science and Business Media LLC
Date: 22-07-2021
DOI: 10.1038/S41477-021-00971-5
Abstract: Stem rust caused by the fungus Puccinia graminis f. sp. tritici (Pgt) is a devastating disease of the global staple crop wheat. Although this disease was largely controlled in the latter half of the twentieth century, new virulent strains of Pgt, such as Ug99, have recently evolved
Publisher: Elsevier BV
Date: 07-2021
Publisher: Springer Science and Business Media LLC
Date: 28-02-2020
DOI: 10.1038/S41467-020-14937-2
Abstract: Stem rust is an important disease of wheat that can be controlled using resistance genes. The gene SuSr-D1 identified in cultivar ‘Canthatch’ suppresses stem rust resistance. SuSr-D1 mutants are resistant to several races of stem rust that are virulent on wild-type plants. Here we identify SuSr-D1 by sequencing flow-sorted chromosomes, mutagenesis, and map-based cloning. The gene encodes Med15, a subunit of the Mediator Complex, a conserved protein complex in eukaryotes that regulates expression of protein-coding genes. Nonsense mutations in Med15b.D result in expression of stem rust resistance. Time-course RNAseq analysis show a significant reduction or complete loss of differential gene expression at 24 h post inoculation in med15b.D mutants, suggesting that transcriptional reprogramming at this time point is not required for immunity to stem rust. Suppression is a common phenomenon and this study provides novel insight into suppression of rust resistance in wheat.
Publisher: Springer Science and Business Media LLC
Date: 07-06-2021
DOI: 10.1038/S41467-021-23738-0
Abstract: The re-emergence of stem rust on wheat in Europe and Africa is reinforcing the ongoing need for durable resistance gene deployment. Here, we isolate from wheat, Sr26 and Sr61 , with both genes independently introduced as alien chromosome introgressions from tall wheat grass ( Thinopyrum ponticum ). Mutational genomics and targeted exome capture identify Sr26 and Sr61 as separate single genes that encode unrelated (34.8%) nucleotide binding site leucine rich repeat proteins. Sr26 and Sr61 are each validated by transgenic complementation using endogenous and/or heterologous promoter sequences. Sr61 orthologs are absent from current Thinopyrum elongatum and wheat pan genome sequences, contrasting with Sr26 where homologues are present. Using gene-specific markers, we validate the presence of both genes on a single recombinant alien segment developed in wheat. The co-location of these genes on a small non-recombinogenic segment simplifies their deployment as a gene stack and potentially enhances their resistance durability.
Publisher: Research Square Platform LLC
Date: 31-10-2022
DOI: 10.21203/RS.3.RS-2208386/V1
Abstract: Most resistance genes thus far isolated from wheat have a very limited number of functional alleles, with the exception of the powdery mildew PM3 resistance locus. Here we report the isolation of most of the alleles at wheat stem rust resistance gene locus SR9 , representing the largest multi-allelic rust resistance locus in common wheat. The seven previously reported resistance alleles ( Sr9a , Sr9b , Sr9d , Sr9e , Sr9f , Sr9g , and Sr9h ) at the locus were characterised using a synergistic strategy. Loss-of-function mutants and/or transgenic complementation were used to confirm Sr9b , two haplotypes of Sr9e ( Sr9e_h1 , Sr9e_h2 ), Sr9g , and Sr9h . Each allele encodes a highly related nucleotide-binding site leucine-rich repeat (NB-LRR) type immune receptor, containing a previously unreported motif at their N termini and an unusual long LRR domain, that confers resistance to a unique spectrum of isolates of the wheat stem rust pathogen. The only SR9 protein effective against stem rust pathogen race TTKSK (Ug99), SR9H, differed from SR9B by a single amino acid. SR9B and SR9G resistance proteins were also distinguished by only a single amino acid. The SR9 allelic series found in the B subgenome are orthologs of wheat stem rust resistance gene Sr21 located in the A subgenome with around 85% identity in protein sequences.
Publisher: Wiley
Date: 15-12-2020
DOI: 10.1111/NPH.17075
Abstract: Pm1a , the first powdery mildew resistance gene described in wheat, is part of a complex resistance (R) gene cluster located in a distal region of chromosome 7AL that has suppressed genetic recombination. A nucleotide‐binding, leucine‐rich repeat (NLR) immune receptor gene was isolated using mutagenesis and R gene enrichment sequencing (MutRenSeq). Stable transformation confirmed Pm1a identity which induced a strong resistance phenotype in transgenic plants upon challenge with avirulent Blumeria graminis (wheat powdery mildew) pathogens. A high‐density genetic map of a B . graminis family segregating for Pm1a avirulence combined with pathogen genome resequencing and RNA sequencing (RNAseq) identified AvrPm1a effector gene candidates. In planta expression identified an effector, with an N terminal Y/FxC motif, that induced a strong hypersensitive response when co‐expressed with Pm1a in Nicotiana benthamiana . Single chromosome enrichment sequencing (ChromSeq) and assembly of chromosome 7A suggested that suppressed recombination around the Pm1a region was due to a rearrangement involving chromosomes 7A, 7B and 7D. The cloning of Pm1a and its identification in a highly rearranged region of chromosome 7A provides insight into the role of chromosomal rearrangements in the evolution of this complex resistance cluster.
Publisher: Oxford University Press (OUP)
Date: 16-06-2018
DOI: 10.1104/PP.17.00435
Publisher: Cold Spring Harbor Laboratory
Date: 22-09-2023
Publisher: Springer Science and Business Media LLC
Date: 16-10-2019
DOI: 10.1007/S00122-018-3201-8
Abstract: A set of molecular markers was developed for Sr26 from comparative genomic analysis. The comparative genomic approach also enabled the identification of a previously uncharacterised wheat chromosome that carried Sr26. Stem rust of wheat, a biotic stress caused by a fungal pathogen, continues to pose significant threats to wheat production. Considerable effort has been directed at surveillance and breeding approaches to minimize the impact of the widely virulent race of the stem rust pathogen (Puccinia graminis f. sp. tritici, Pgt) commonly known as Ug99 (TTKSK) and other races in its lineage. The stem rust resistance gene Sr26, derived from Thinopyrum ponticum, is an excellent ex le of the successful utilization of a gene from a wild relative of a crop plant and remains one of the few durable sources of resistance currently effective against all known field isolates of Pgt. We explored comparative genomic analysis of the nucleotide binding leucine rich repeat (NLR) genes of the diploid D genome and bread wheat genomes to target the Sr26 region from the non-sequenced Th. ponticum genome. A chromosomal interval harboring NLR genes in the distal end of homoeologous group 6 chromosomes was used to demarcate the Sr26 locus. A set of closely linked PCR-based molecular markers was developed for Sr26. Furthermore, the comparative analysis approach enabled the unambiguous identification of a previously uncharacterised wheat chromosome that carried Sr26 in an introgressed Th. ponticum segment and was validated by fluorescent and genomic in situ hybridisation (FISH/GISH) experiments. The genetic information generated from the target interval based on this study will benefit future related studies on group 6 chromosomes of wheat, including 6D
Publisher: Springer Science and Business Media LLC
Date: 29-09-2022
DOI: 10.1007/S00122-022-04221-W
Abstract: Stripe rust resistance gene YrAet672 from Aegilops tauschii accession CPI110672 encodes a nucleotide-binding and leucine-rich repeat domain containing protein similar to YrAS2388 and both these members were haplotypes of Yr28. New sources of host resistance are required to counter the continued emergence of new pathotypes of the wheat stripe rust pathogen Puccinia striiformis Westend. f. sp. tritici Erikss. (Pst). Here, we show that CPI110672, an Aegilops tauschii accession from Turkmenistan, carries a single Pst resistance gene, YrAet672, that is effective against multiple Pst pathotypes, including the four predominant Pst lineages present in Australia. The YRAet672 locus was fine mapped to the short arm of chromosome 4D, and a nucleotide-binding and leucine-rich repeat gene was identified at the locus. A transgene encoding the YrAet672 genomic sequence, but lacking a copy of a duplicated sequence present in the 3' UTR, was transformed into wheat cultivar Fielder and Avocet S. This transgene conferred a weak resistance response, suggesting that the duplicated 3' UTR region was essential for function. Subsequent analyses demonstrated that YrAet672 is the same as two other Pst resistance genes described in Ae. tauschii, namely YrAS2388 and Yr28. They were identified as haplotypes encoding identical protein sequences but are polymorphic in non-translated regions of the gene. Suppression of resistance conferred by YrAet672 and Yr28 in synthetic hexaploid wheat lines (AABBDD) involving Langdon (AABB) as the tetraploid parent was associated with a reduction in transcript accumulation.
Publisher: Oxford University Press (OUP)
Date: 22-06-2022
DOI: 10.1093/G3JOURNAL/JKAC149
Abstract: Advances in sequencing technologies as well as development of algorithms and workflows have made it possible to generate fully phased genome references for organisms with nonhaploid genomes such as dikaryotic rust fungi. To enable discovery of pathogen effectors and further our understanding of virulence evolution, we generated a chromosome-scale assembly for each of the 2 nuclear genomes of the oat crown rust pathogen, Puccinia coronata f. sp. avenae (Pca). This resource complements 2 previously released partially phased genome references of Pca, which display virulence traits absent in the isolate of historic race 203 (isolate Pca203) which was selected for this genome project. A fully phased, chromosome-level reference for Pca203 was generated using PacBio reads and Hi-C data and a recently developed pipeline named NuclearPhaser for phase assignment of contigs and phase switch correction. With 18 chromosomes in each haplotype and a total size of 208.10 Mbp, Pca203 has the same number of chromosomes as other cereal rust fungi such as Puccinia graminis f. sp. tritici and Puccinia triticina, the causal agents of wheat stem rust and wheat leaf rust, respectively. The Pca203 reference marks the third fully phased chromosome-level assembly of a cereal rust to date. Here, we demonstrate that the chromosomes of these 3 Puccinia species are syntenous and that chromosomal size variations are primarily due to differences in repeat element content.
Publisher: Springer Science and Business Media LLC
Date: 26-10-2023
Location: Australia
No related grants have been discovered for Timothy Hewitt.