Recently, the team led by Dr. He Huagang from School of Life Sciences of Jiangsu University (JSU) published an research article, titled “An NLR pair in the Pm68 locus confers powdery mildew resistance in durum and common wheat”, in Nature Communications. This article reported the map-based cloning of the new powdery mildew resistance gene Pm68 and revealed the evolution and resistance mechanism at the molecule level. Dr. He Huagang was the first and corresponding author, and the collaborators Dr. Gao Anli from Henan University and Dr. Wang Yajun from Centre for Excellence in Molecular Plant Sciences of Chinese Academy of Sciences were listed as co-corresponding authors.
Common wheat and durum wheat are two related species with distinct grain properties and end use purposes. Both common and durum wheat productions are frequently challenged by powdery mildew, caused by the obligate biotrophic pathogen Blumeria graminis f. sp. tritici. The mining and utilization of powdery mildew resistance genes are crucial for the management of powdery mildew of common wheat and durum wheat. In 2021, Dr. He first reported the new powdery mildew resistance gene Pm68 on chromosome 2BS in the Greek durum wheat accession TRI 1796 and demonstrated the potential to be used for breeding.
In the recent article, Dr. He and his collaborators made new progress. Through fine genetic mapping and molecular marker-based association analyses, the authors narrowed the Pm68 locus to the interval flanked by markers Xdw08/Xdw09. Genome sequencing by PacBio and read-mapping using the transcriptome data showed that two NLR genes, Pm68-1 and Pm68-2, in the Pm68 locus were highly related to disease resistance. So, the authors transformed the two genes into the powdery mildew-susceptible wheat variety Fielder. The data showed that the transgenic wheat lines only carrying Pm68-1 or Pm68-2 were susceptible to powdery mildew, whereas the transgenic lines carrying Pm68-1 and Pm68-2 were highly resistant to this disease. It was strongly suggested that the Pm68 resistance were controlled by the NLR pair Pm68-1 and Pm68-2. Evolutionary analysis revealed that Pm68 originated from wild emmer wheat. And then, the researchers found nine haplotypes from wild emmer wheat accessions.
To test the function relationship of Pm68-1 and Pm68-2, the researchers constructed a series of vectors and over-expressed them in tobacco leaves. The results demonstrated that co-expression of Pm68-1 and Pm68-2 could induce cell death in the leaves but single Pm68-1 or Pm68-2 could not. Mutation analysis of the MHD and P-loop motifs showed that only Pm68-1 was associated with inducing of cell death. The authors also found that only co-expression of the full-length Pm68-1 and Pm68-2 CCl domain could trigger cell death. Therefore, Pm68-1 was the key executor triggering cell death and its activity was regulated by the CCl domain of Pm68-2. Co-IP assay further confirmed that Pm68-1 interacted with Pm68-2 and its three domains.
The researchers transferred the gene Pm68 from durum wheat TRI 1796 into the elite wheat variety Yangmai 158 (YM158) by interspecific crossing and obtained stable introgression lines carrying Pm68. These wheat lines showed powdery mildew resistance at both the seedling and the adult plant stages and some agronomic traits were better than Yangmai 158, indicating great value for resistance breeding in common wheat and durum wheat.
In general, Dr. He’s team successfully cloned the new powdery mildew resistance gene Pm68 from durum wheat that was controlled by two NLR genes and revealed the interaction patterns of their corresponding proteins. They also developed new powdery mildew-resistant common wheat lines that have excellent agronomic traits.
(Source: School of Life Sciences)
