Structural and functional analysis of the broad spectrum rice blast resistance gene Ptr in US rice germplasm

Authors: Jia, Yulin

Submitted to: International Rice Blast Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/17/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Rice blast resistance (R) genes Pi-ta/Pi-ta2/Ptr near the centromere of chromosome 12 have been effectively deployed to prevent infections by M. oryzae for decades worldwide. Genetic analysis revealed that Ptr confers broad spectrum disease resistance independent of Pi-ta. Here we report structural and functional analysis of the Ptr gene in rice. The Ptr gene was mapped within a 63 kilobase region using 12,000 segregating progenies from the cross of the resistant rice variety Katy with a susceptible rice variety Amane. Comparing the protein coding regions within a 63 kb we identified 23 SNPs and four InDels that distinguish Katy from Amane. Among them, five SNPs resulting in nonsynonymous mutations and one 12 base pair deletion resulting in a 4 amino acid deletion defines the functional region of Ptr in the last exon of Ptr. The Ptr gene encodes two predicted proteins with 4 armadillo repeats that were mainly localized in the cytoplasm of plant cells. A two-base pair deletion within the Ptr coding region in the fast neutron-created mutant line M2354 produced a truncated protein, resulting in susceptibility to M. oryzae. Targeted mutation of Ptr in a resistant cultivar using CRISPR/Cas9 led to blast susceptibility, further validating its resistance function. A new haplotype of Ptr was identified from a black hull awned weedy red rice (PtrBHA) responsible for preventing the infections by a highly virulent blast race IB33. Weedy red rice is known to compete with commercial rice, and functional validation of PtrBHA will shed more insights into evolution of plant innate immunity. This new knowledge will aid to develop strategies to effectively manage rice blast disease.