Figure 1 .

Schematic for VIB-1 regulation of HI and cell death. VIB-1 is required for HI mediated by genetic differences at mating type, het-6, and het-c pin-c (Xiang and Glass 2002, 2004; Lafontaine and Smith 2012) in addition to activating PCD through additional unknown downstream effectors (Dementhon et al. 2006). het-6 incompatibility is mediated by un-24 (ribonucleotide reductase) and het-6 interactions (Micali and Smith 2006; Lafontaine and Smith 2012); mating-type incompatibility is mediated by mating type A-1, mating type a-1, and tol (Pittenger 1957; Newmeyer 1970; Glass et al. 1990; Shiu and Glass 1999); while het-c incompatibility is mediated by het-c pin-c interactions (Glass and Kaneko 2003; Kaneko et al. 2006); alternative HET-C polypeptides have been shown to physically interact (Sarkar et al. 2002). Phenotypic consequences of HI in N. crassa include growth inhibition and suppression of conidiation (Perkins 1988). Hyphal compartments within heterokaryons that carry alternate het haplotypes (such as het-c/pin-c, rnr/het-6, or mat-a/A/tol) undergo compartmentation and rapid cell death (Glass and Kaneko 2003) and thus stain positive for vital dyes such as methylene blue (arrows).