van Wetter M A, Wösten H A, Wessels J G
Groningen Biomolecular Sciences and Biotechnology Institute, Laboratory of Molecular Plant Biology and Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
Mol Microbiol. 2000 Apr;36(1):201-10. doi: 10.1046/j.1365-2958.2000.01848.x.
Two monokaryons of Schizophyllum commune can form a fertile dikaryon when the mating-type genes differ. Monokaryons form sterile aerial hyphae, while dikaryons also form fruiting bodies that function in sexual reproduction. The SC3 hydrophobin gene is expressed both in monokaryons and in dikaryons. The SC4 hydrophobin is dikaryon specific. In the monokaryon, SC3 lowers the water surface tension, coats aerial hyphae with a hydrophobic layer and mediates attachment of hyphae to hydrophobic surfaces. The SC4 protein lines gas channels within fruiting bodies with a hydrophobic membrane. Using gene disruptions, in this study, we show that in dikaryons SC3 fulfils the same roles as in monokaryons. SC4, on the other hand, has a role within fruiting bodies. In contrast to gas channels in fruiting bodies of the wild type, those of a DeltaSC4 strain easily filled with water. Thus, SC4 prevents gas channels filling with water under wet conditions, probably serving uninterrupted gas exchange. Other dikaryon-specific hydrophobin genes, SC1 and SC6, apparently do not substitute for the SC4 gene. In addition, by expressing the SC4 gene behind the SC3 promoter in a DeltaSC3 monokaryon, it was shown that SC4 cannot fully substitute for SC3, indicating that both hydrophobins evolved to fulfil specific functions.
裂褶菌的两个单核体在交配型基因不同时可形成可育双核体。单核体形成不育的气生菌丝，而双核体还形成在有性生殖中起作用的子实体。SC3疏水蛋白基因在单核体和双核体中均有表达。SC4疏水蛋白是双核体特异性的。在单核体中，SC3降低水面张力，用气生菌丝覆盖疏水层，并介导菌丝附着于疏水表面。SC4蛋白用疏水膜排列子实体内的气体通道。在本研究中，通过基因敲除，我们表明在双核体中SC3发挥与在单核体中相同的作用。另一方面，SC4在子实体内起作用。与野生型子实体中的气体通道不同，ΔSC4菌株的气体通道很容易充满水。因此，SC4可防止气体通道在潮湿条件下充满水，可能有助于不间断的气体交换。其他双核体特异性疏水蛋白基因SC1和SC6显然不能替代SC4基因。此外，通过在ΔSC3单核体中SC3启动子后表达SC4基因，表明SC4不能完全替代SC3，这表明两种疏水蛋白都进化以履行特定功能。
