Genetic regulation of emergent growth in Schizophyllum commune

Abstract

After a period of juvenile growth, Schizophyllum commune starts to transcribe genes for a number of abundant cell-wall proteins that are excreted into the medium by submerged hyphae but become part of the cell wall in emergent structures. The dikaryon transcribes the genes SC1, SC3, 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 forms an insoluble hydrophobic rodlet layer by interfacial self-assembly at the outer surface of aerial hyphae of both monokaryon and dikaryon. The SC4p hydrophobin forms an insoluble membrane separating the extracellular matrix surrounding dikaryotic hyphae of the plectenchyma from air cavities in the fruit bodies while the product of the SC7 gene is found within the extracellular matrix. However, these plectenchyma hyphae do not express the SC3 gene. Because SC3 activity is suppressed in a MATA = MATB≠ heterokaryon and a MATAx matBCon homokaryon, interaction between different B mating-type gene products appears responsible for suppression of SC3 in the hyphae that form the plectenchyma. On the other hand, in aerial hyphae of the MATA ≠ MATB≠ heterokaryon the binucleate state of the hyphae appears disrupted and this is accompanied by expression of SC3 only, as in the monokaryon. This suggests that regulation of specific genes by the products of different MATB genes only occurs when these genes are present in closely paired nuclei. Thus, spatial differences in gene expression during emergent growth in the MATA ≠ MATB≠ heterokaryon may occur by regulation of the nuclear distribution. Key words: Schizophyllum commune development, hydrophobins in development, mating-type genes in Schizophyllum, fruit-body development, emergent growth.