In the Basidiomycotina, the processes of hyphal fusion, nuclear migration and subsequently the selective association of nuclei convert a monokaryotic hypha into a dikaryotic hypha. The dikaryotic hyphae produce the fruit bodies. A small backwardly projecting outgrowth (hook) occurs from the end cell of hypha into which one of the two daughter nuclei passes (Figure 2.5). Septa form and the hook cell then fuses with the penultimate cell, forming clamp connections at the septa and the process is repeated. The simultaneous division of nuclei, formation of hook cell and its fusion with the penultimate cell ensures that each cell of the mycelium contains two genetically distinct nuclei. Recent work suggests that whether nuclei are juxtaposed or separated can be important in gene regulation (Schuurs et al., 1998). The fruiting body of Schizophyllum commune (Basidiomycotina) is rich in proteins called hydrophobins (Chapter 1). The type of hydrophobins secreted is determined by immunochemical staining methods. The monokaryotic hyphae secreted hydrophobin SC3 but not hydrophobins SC4 and SC7. Conversely, the type of hydrophobin secreted by the dikaryotic hyphae is determined on the inter-nuclear distance which could be manipulated by growth on a hydrophobic or hydrophilic surface. On a hydrophilic surface, the nuclei were adjacent (1.6 ^m) and the hypha secreted SC4 hydrophobin (which coats
Dikaryotic cell r i
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