Heterokaryon incompatibility function of barrage-associated vegetative incompatibility genes (vic) in Cryphonectria parasitica

Abstract

Six vegetative incompatibility (vic) loci have been identified in Cryphonectria parasitica based on barrage formation during mycelial interactions. We used hygromycin B- and benomyl-resistance as forcing markers in C. parasitica strains to test whether heteroallelism at each vic locus prevents heterokaryon formation following mycelial interactions. Paired strains that had allelic differences at any of vic1, 2, 3, 6 or 7 but not vic4 displayed heterokaryon incompatibility function, as recognized by slow growth or aberrant morphology. While clearly forming barrages in mycelial interactions, paired strains with different alleles at vic4 formed stable heterokaryons. With examples from other fungi, this inconsistency at vic4 suggests that barrage formation and heterokaryon incompatibility are not different manifestations of the same process. Rather, the evidence indicates that heterokaryon incompatibility represents a component of a vegetative incompatibility system that may also use cell-surface or extracellular factors to trigger programmed cell death to modulate nonself recognition in fungi.

• chestnut blight fungus
• programmed cell death
• virus transmission

This work was financed by McIntire-Stennis Project NYC 153553 to MGM, NSERC Discovery Grant to MLS and NSERC Graduate Scholarship to CCG. Thanks also to A. Churchill for providing fungal strains.