An allelic variant of the broad-spectrum blast resistance gene Ptr in weedy rice is associated with resistance to the most virulent blast race IB-33

Authors: ZHAO, HAIJUN - Noble Research Institute; LIU, YAN - University Of Arkansas; Jia, Melissa; Jia, Yulin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2021
Publication Date: 5/3/2022
Citation: Zhao, H., Liu, Y., Jia, M.H., Jia, Y. 2022. An allelic variant of the broad-spectrum blast resistance gene Ptr in weedy rice is associated with resistance to the most virulent blast race IB-33. Plant Disease. https://doi.org/10.1094/PDIS-09-21-2043-RE.
DOI: https://doi.org/10.1094/PDIS-09-21-2043-RE

Interpretive Summary: Rice resistance (R) genes have been effectively deployed to prevent blast disease caused by the pathogen Magnaporthe oryzae, one of the most serious threats for stable rice production worldwide. Weedy rice, competing with cultivated rice, may carry novel or lost R genes. In the present study. we examine the resistance mechanism of weedy rice to M. oryzae. The Ptr gene in rice encodes a protein with 4 armadillo repeats and confers a broad spectrum of blast resistance except for Race IB33. A blast resistance QTL qBR12.3b was previously mapped between two single nucleotide polymorphism (SNP) markers 10,633,942 bp and 10,820,033 bp in a black hulled awned weedy strain using a weed-crop mapping population under greenhouse conditions. A gene-specific marker was developed from Ptr to distinguish alleles in weed and crop. The existence of the Ptr gene in 207 individuals of the same mapping population was examined using this gene-specific marker. Disease reactions of 207 individuals and their parents to IB33 were evaluated. The resistant individuals had the Ptr whereas the susceptible individuals did not. Sequence analysis of the Ptr gene from weedy rice, PtrBHA, identified a unique amino acid glutamine (Gln) at protein position 874. Minor changes of protein conformation of the PtrBHA gene were identified through structure analysis of PtrBHA. These findings are useful to determine if Gln874 in the PtrBHA protein determines the PtrBHA mediated disease resistance responses.

Technical Abstract: Rice resistance (R) genes have been effectively deployed to prevent blast disease caused by the pathogen Magnaporthe oryzae which is one of the most serious threats for stable rice production worldwide. Weedy rice competing with cultivated rice may carry novel R genes. In the present study, we examined if weedy rice has novel a resistance to M. oryzae. The Ptr gene in rice encodes a protein with 4 armadillo repeats and confers a broad spectrum of blast resistance, except for Race IB33. A blast resistance QTL qBR12.3b was previously mapped between two single nucleotide polymorphism (SNP) markers 10,633,942 bp and 10,820,033 bp in a black hulled/awned weedy strain. A pair of gene- specific markers was developed to distinguish the weed and crop Ptr alleles within this region. Using the gene-specific markers, the PtrBHA allele was found in individuals of a weed-crop mapping population. Disease reactions of the mapping population to Race IB33 were determined, and the resistant individuals were fully correlated with the presence of PtrBHA, whereas the susceptible individuals lacked the PtrBHA allele. Sequence analysis identified a unique glutamine (Gln) amino acid at position 874 in PtrBHA. Structure analysis predicted that the protein conformation differed between the resistant PtrBHA and the susceptible Ptr allele. These findings support the conclusion that the novel PtrBHA allele from weedy rice mediates blast resistance to Race IB33.