Survival of the quickest: Pathogen pressure drives rapid evolution at a barley resistance gene cluster
Primary Author: Karl Effertz
Faculty Sponsor: Robert Brueggeman
Primary College/Unit: Agricultural, Human and Natural Resource Sciences
Category: Agricultural and Natural Resource Sciences
Net form net blotch (NFNB), caused by the fungal pathogen Pyrenophora teres f. teres (Ptt), results in significant yield loss in effected barley fields worldwide. An important region on barley chromosome 6H has been reported in several studies investigating Ptt resistance and susceptibility. Our group investigated this region, which confers susceptibility or resistance to Ptt, depending on fungal isolate and barley cultivar. Our research has uncovered a unique adaptive mechanism that allows barley plants to rapidly exchange resistance genes in response to pathogen attack.
Using DNA markers, we analyzed three separate barley populations to delimit the 6H region associated with Ptt resistance by correlating marker alleles with disease outcome.
Our results indicate that the 6H disease resistance cluster covers 3 MB of the genome, containing 36 genes. Of these, four genes resemble disease resistance genes that have been previously characterized. Strikingly, this resistance cluster consistently transfers as a block, with ~5% of individuals from each population harboring a double recombination event where only this block of genes transfers from parent to progeny. The conserved nature of recombination at this site suggests an evolutionary mechanism where the barley plant can rapidly exchange resistance genes in the face of pathogen pressure. This directed recombination bears similarity to mammalian VDJ recombination, an adaptive mechanism allowing for diverse immune responses. The discovery of this mechanism in plants would create a new paradigm for describing host-parasite evolution and breeding for disease resistance.