Ducks in a row: multiple effectors of Pyrenophora teres f. teres target a single host susceptibility locus in barley
Pyrenophora teres f. teres causes net form net blotch in barley. A biparental population of isolates 15A and 6A was used to identify two quantitative trait loci (QTL), VR1 and VR2, associated with virulence on Rika barley. Two effector gene candidates, VR1 and VR2, were selected for functional analysis. Both genes were universally present in a global P. teres f. teres collection with VR1 encoding for a secreted peptidase and VR2 for a secreted hypothetical protein. Single and double VR1 and VR2 gene disruptions in isolate 6A caused a significant reduction in virulence on Rika. Gene-edited strains acquiring the virulent 6A VR1 and VR2 alleles became more virulent on Rika. Inoculation of the gene-edited strains onto the Rika × Kombar (RK) host population showed that both VR1 and VR2 targeted the susceptibility locus Spt1 in Rika. Therefore, VR1 and VR2 act as effector genes and independently contribute to virulence by targeting the susceptibility locus Spt1. Interestingly, a significant QTL targeting Spt1 was still observed when the 6A VR1 and VR2 double mutant (6AΔvr1Δvr2) was inoculated onto the RK population. Therefore, since 6AΔvr1Δvr2 was still virulent and this virulence targeted Spt1, additional effectors are likely produced by 6A and may be harboured in the VR1 or VR2 QTL.