Heterokaryon incompatibility (HI) in filamentous fungi is a form of nonself recognition that operates during the vegetative phase of the life cycle. One HI gene complex in Neurospora crassa, the het-6 locus, comprises two incompatibility genes, het-6 and un-24, each having two allelic variants, Oak Ridge (OR) and Panama (PA). The un-24 gene also encodes the large subunit of ribonucleotide reductase while het-6 appears to be a member of a repetitive gene family with no other known function aside from HI. These two genes are in severe linkage disequilibrium such that only un-24 OR het-6 OR and un-24 PA het-6 PA haplotypes occur in nature. In this study we unravel several genetic interactions that govern the HI functions of this gene complex. We use novel un-24 PA het-6 OR strains and het-6 deletion strains to demonstrate that nonallelic interactions occur between un-24 and het-6 and reveal an allelic incompatibility interaction between the OR and PA forms of un-24 that is asymmetrically enhanced by the presence of het-6 OR or het-6 PA. We also show how two allelic forms of vib-1, a suppressor of het-c- and mat-associated incompatibility, differentially act as recessive suppressors of HI associated with nonallelic interactions between un-24 PA and het-6 OR. In contrast, vib-1 is a dominant suppressor of HI associated with allelic differences at un-24 and a dominant partial suppressor of the un-24 OR and het-6 PA nonallelic interaction. The range of suppressor activities is largely explained by an interesting differential effect on het-6 OR and het-6 PA transcript levels by VIB-1.

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Keywords HET domain, Nonallelic heterokaryon incompatibility, Nonself recognition, Ribonucleotide reductase
Persistent URL dx.doi.org/10.1016/j.fgb.2011.11.001
Journal Fungal Genetics and Biology
Lafontaine, D.L. (Denis L.), & Smith, M. (2012). Diverse interactions mediate asymmetric incompatibility by the het-6 supergene complex in Neurospora crassa. Fungal Genetics and Biology, 49(1), 65–73. doi:10.1016/j.fgb.2011.11.001