Different temporal and spatial expression of two hydrophobin-encoding genes of the edible mushroom Agaricus bisporus

In a search for genes that are only expressed in fruit bodies of the basidi omycete Agaricus bisporus, two cDNAs, hypA and hypB that encode hydrophobin s have been isolated previously. In this study, the structure of hypB is re solved and it is shown that the two genes are differentially expressed, ind icating that the encoded hydrophobins serve different functions in A. bispo rus mushrooms. hypB encodes a polypeptide (HYPB) of 119 aa that shows littl e sequence identity with HYPA apart from the characteristic arrangement of eight cysteines found exclusively in hydrophobins. The temporal and spatial expression of the two hydrophobin-encoding genes during fruit body develop ment was compared using Northern analysis and in situ hybridization, Accumu lation of hypA mRNA was found in tissue fractions consisting of undifferent iated white hyphae. In situ hybridization showed that the highest hypA mRNA levels are not found in the outermost cell layers of the pileipellis but i n the cell layers adjacent to that. The highest level of expression of hypB occurs early in development when the primordium differentiates into densel y packed, randomly oriented cap hyphae and loosely packed, vertically orien ted stipe hyphae. In mature mushrooms, a strong accumulation of hypB transc ripts was found only in the transitional zone between cap and stipe tissue, demonstrating that transcription regulation of hypB is clearly distinct fr om hypA.