GENETIC-REGULATION OF EMERGENT GROWTH IN SCHIZOPHYLLUM-COMMUNE

After a period of juvenile growth, Schizophyllum commune starts to tra nscribe genes for a number of abundant cell-wall proteins that are exc reted into the medium by submerged hyphae but become part of the cell wall in emergent structures. The dikaryon transcribes the genes SC1, S C3, SC4, and SC6 that encode hydrophobins and SC7 and SC14 that encode hydrophilic wall proteins of unknown function. Of these, only the SC3 gene is highly transcribed in the monokaryon. The SC3p hydrophobin fo rms an insoluble hydrophobic rodlet layer by interfacial self-assembly Bt the outer surface of aerial hyphae of both monokaryon and dikaryon . The SC4p hydrophobin forms an insoluble membrane separating the extr acellular matrix surrounding dikaryotic hyphae of the plectenchyma fro m air cavities in the fruit bodies while the product of the SC7 gene i s found within the extracellular matrix. However, these plectenchyma h yphae do not express the SC3 gene. Because SC3 activity is suppressed in a MATA= MATB not equal heterokaryon and a MATAx matB(con) homokaryo n, interaction between different B mating-type gene products appears r esponsible for suppression of SC3 in the hyphae that form the plectenc hyma. On the other hand, in aerial hyphae of the MATA not equal MATB n ot equal heterokaryon the binucleate state of the hyphae appears disru pted and this is accompanied by expression of SC3 only, as in the mono karyon. This suggests that regulation of specific genes by the product s of different MATE genes only occurs when these genes are present in closely paired nuclei. Thus, spatial differences in gene expression du ring emergent growth in the MATA not equal MATB not equal heterokaryon may occur by regulation of the nuclear distribution.