Figure 7.

Model for heterokaryon incompatibility mediated by genetic differences at het-c/pin-c. When a hyphal compartment is heterozygous for het-c and pin-c (for example, during a hyphal fusion event or in a partial diploid constructed via a cross or by transformation), nonself recognition is mediated by interactions between HET-C and PIN-C encoded by alternative haplotypes. The recognition event is predicted to occur at the plasma membrane because HET-C is a plasma membrane protein (Sarkar et al. 2002) and PIN-C is predicted to reside in the cytoplasm. The nonself recognition signal is amplified by HET-C1/PIN-C2, HET-C2/PIN-C1, and HET-C1/HET-C2 interactions. The signal is transduced to VIB-1, which is predicted to encode a transcription factor (Xiang and Glass 2002). VIB-1 is required for the repression of conidiation, growth inhibition, and hyphal compartmentation and death. Other factors are also important, because mutations at vib-1 do not completely suppress HI.