Sorghum ANTHRACNOSE RESISTANCE GENE3 Is a Non-Coding RNA That Confers Fungal Resistance through Enhanced Cell Death

Abstract

The fungal pathogen Colletotrichum sublineola is a major constraint to sorghum production. The sorghum genotype IS18760 is resistant to multiple C. sublineola strains, but the genetic basis of this resistance is unknown. Bulk segregant analysis using whole-genome resequencing of a biparental mapping population identified a major resistance locus, designated ANTHRACNOSE RESISTANCE GENE LOCUS 3 (ARG3), associated with extensive cell death. Fine mapping delimited the ARG3 locus to a 30 kb interval containing three predicted protein-coding genes and one unannotated non-coding RNA gene. Among these, only the non-coding RNA gene showed consistent sequence polymorphisms between resistant and susceptible lines and elevated pathogen-induced expression in the resistant parent, suggesting that it underlies ARG3-mediated resistance. Regions syntenic to ARG3 across grass species contain conserved non-coding sequences enriched for H3K27me3 and H2A.Z chromatin marks, suggesting a conserved regulatory function. The resistance allele is absent from a 111-line sorghum pangenome. The resistant sorghum line harboring ARG3 and the corresponding avirulent pathogen strain originate from the same geographic region, suggesting co-evolution between host resistance and a prevalent pathogen strain. Phylogenetic analysis suggests that loss of resistance in susceptible lines may relate to insertion of a 12.4 kb repetitive sequence. Importantly, silencing of the ARG3 transcript in the resistant parental line abrogated resistance to C. sublineola, confirming that ARG3 non-coding RNA gene underlies the fungal resistance mediated by the ARG3 locus in IS18760. These lines of evidence show that ARG3 is an important target for resistance breeding and provide new insight into non-coding RNA-mediated disease resistance.