Transgenerational gene silencing causes gain of virulence in a plant pathogen

Abstract

Avirulence ( Avr) genes of plant pathogens encode effector proteins that trigger immunity in plants carrying appropriate resistance ( R) genes. The Phytophthora sojae Avr3a gene displays allelic variation in messenger RNA transcript levels. P. sojae strains with detectable Avr3a gene transcripts are avirulent on plants carrying the R-gene Rps3a, whereas strains lacking Avr3a mRNA escape detection by Rps3a and are virulent. Here we show non-Mendelian interactions between naturally occurring Avr3a alleles that result in transgenerational gene silencing, and we identify small RNA molecules of 25 nucleotides that are abundant in gene-silenced strains but not in strains with Avr3a mRNA. This example of transgenerational gene silencing is exceptional because it is naturally occurring and results in gain of virulence in a pathogenic organism.

Abstract

Plant pathogens encode effector proteins that trigger immunity in plants carrying appropriate resistance genes. Here Qutob et al. show non-Mendelian interactions between naturally occurring Phytophthora sojae alleles that result in transgenerational gene silencing and gain of virulence in soybean plants.