The b alleles of U. Fly and frog homeo domains show homologies with yeast mating type regulatory proteins. The A locus of Schizophyllum commune encodes two dissimilar multiallelic homeodomain proteins. A fungal mating type protein that regulates asexual and sexual development contains a POU-related domain. This content is only available via PDF. Email alerts Article activity alert.
Accepted manuscripts alert. Table of contents alert. Latest published articles alert. View Metrics. Cited by Google Scholar. Social media. The Node preLights FocalPlane. Grants Journal Meetings Workshops. Library hub Company news Contacts. The crozier and the clamp cell fuse arrowed with the newly formed subterminal cell to restore a binucleate cell organisation. The new tip cell in the ascogenous hypha becomes an ascus in which nuclear fusion, meiosis and sporulation occurs and the dikaryophase is proliferated from the subterminal cell.
Pheromone binding induces the formation of mating filaments that fuse at their tips to generate a cell that initiates growth of a filamentous dikaryon Spellig et al, In mushroom species, the asexual stage is filamentous and is known as a monokaryon homokaryon.
Pheromones appear to have no role in cell fusion in mushroom species; this is mating type-independent. Pheromone signalling is activated after cell fusion and is necessary to initiate and maintain the dikaryophase Olesnicky et al, The mating type loci of U. In both species, there are two unlinked loci and compatible mates are those that have different alleles of genes at both reviewed by Casselton and Olesnicky, One locus b in U.
At the second mating type locus a in U. The thousands of mating types we see in mushrooms have been generated by gene duplication. There are three paralogous groups of genes that encode functionally redundant proteins Figure 1. All the genes are multiallelic and over the course of evolution, there has been recombination between the different groups to generate all possible combinations of their different allelic versions May and Matzke, Even larger numbers of A and B gene alleles in S.
In this species, recombination occurs regularly between the paralogous groups of genes because these are separated by homologous DNA sequence. The evolution of multiple mating types has imposed strong selection for highly specific protein—protein interactions that are not necessary where only two mating types exist. Both classes of homeodomain proteins are present in unmated cells encoded by genes at the same mating type locus, and these are unable to heterodimerise to form an active transcription factor.
Dimerisation is only possible when proteins encoded by different allelic versions of the genes are brought together on mating. The mushroom species appear to be unique in having large families of receptors and pheromones. These molecules also display remarkable specificity. None of the receptors are activated by pheromones encoded by genes within the same locus, only different allelic versions of pheromones and receptors brought together on mating are able to activate each other Olesnicky et al, As in the yeasts, pheromone binding to compatible receptors activates a MAP kinase cascade, several components of which have been identified in U.
Significantly the target transcription factor of this pathway, termed Prf1, appears to be a homologue of the S. Like the ste11 gene, prf1 is induced by nutritional starvation, and once induced, Prf1 autoregulates its own transcription in response to pheromone stimulation. Interestingly, only pheromones belonging to the S.
Despite having no obvious sequence similarity to a -factor precursor, pheromone genes from both C. Pheromone processing, as expected, appears to be MAT a cell-dependent, indicating that processing is via the normal a -factor maturation pathway and that this pathway is highly conserved in what are quite distantly related fungi Olesnicky et al, In species such as Neurospora crassa and Podospora anserina , two model species, mating is initiated between differentiated male and female cells, the microconidium and the ascogonium, respectively.
The microconidium fuses with the trichogyne, the receptive tip of the ascogonial hypha, and its nucleus replicates with resident nuclei Figure 2. Nuclear sorting follows to generate typically binucleate dikaryotic cells, the ascogenous hyphae, in which synchronised nuclear division occurs and daughter nuclei are partitioned via a structure analogous to the clamp connection seen in basidiomycete dikaryons. Thus filamentous ascomycetes, like the basidiomycetes, delay nuclear fusion and proliferate the nuclei of a mating pair with a dikaryophase.
This phase is of limited duration in ascomycetes and is confined within the developing fruiting body. The similarities between the ascogenous hyphae and the basidiomycete dikaryon illustrated in Figure 2 clearly point to strong conservation in the way the mating pathways of these fungi are regulated, but this is not immediately obvious when one looks at the genes sequestered at the mating type locus!
The idiomorphs of the P. Interestingly these two genes are the only genes to be found in the idiomorphs of less closely related species Turgeon et al, ; Turgeon, Both genes have obvious homologues in the yeast mating type loci. FMR1 encodes a homologue of S. SMR2 encodes another member of the HMG domain family and is required to maintain proper nuclear pairing in the ascogenous hyphae Zickler et al, , which by analogy to the dikaryon of basidiomycetes is predicted to be dependent on the pheromone signal.
It seems likely that SMR2 is the P. There is no obvious advantage in having this gene sequestered into a mating type locus, as evidenced by the fact that not all filametous ascomycetes do so, but the fact that it can be indicates that its function is required only after cell fusion.
Sexual development requires the co-ordinated activities of a series of transcriptional regulators. By separating the genes that encode one or more of these into idiomorphic mating type loci, mating becomes essential in order to complete the necessary regulatory network.
Amongst ascomycetes, different genes have been elected to fulfil the mating type role. A different strategy has evolved to prevent selfing. Only proteins that interact with another protein are encoded at the mating type loci and these have evolved to be so specific in their interactions that only proteins from different mates can activate sexual development.
HMG proteins play a prominant role in mate recognition and sexual development in all but S. Recent work on C. Significant or not, this family of proteins also plays a key role in sex determination in mammals! Sinclair et al, Studies on the fungal homeodomain mating proteins have contributed immensely to our understanding of the ways in which these transcription factors acquire their specificity Johnson, ; Li et al, Similar studies on the fungal HMG mating proteins promise to be equally rewarding van Beest et al, An N-terminal dimerization domain permits homeodomain proteins to choose compatible partners and initiate sexual development in the mushroom Coprinus cinereus.
Plant Cell , 7 : — Bannuett, F Genetics of Ustilago maydis , a fungal pathogen that induces tumours in maize. Annu Rev Genet , 29 : — Google Scholar. Bistis, GN Evidence for diffusible, mating-type-specific trichogyne attractants in Neurospora crassa.
Exp Mycol , 7 : — USA , pp — Nasmyth K. Thatchell K. Rine J. Jensen R. Hagen D. Blair L. Herskowitz I. Bender A. Sprague G. Goutte C. Johnson A. Froeliger E. Leong S. Glass N. Vollmer S. Staben C. Grotelueschen J. Yanofsky C. Lorimer I. Lasure L. Raju N. Picard M. Debuchy R. Coppin E. Kniep H. Banuett F. Holliday R. Rowell J. DeVay J. Kahmann R. Urban M. Spelling T. Lottspeich F. Frank R. Day P. Anagnostakis S. Puhalla J. Gillissen B. Bergemann J.
Sandmann C. Schroeer B. Kronstad J. Schulz B. Dahl M. Schlesinger R. Martin T. Yee A. Regenfelder E. Reichmann M. Schauwecker F. Bohlmann R. Romeis T. Bakkeren G. Elliott T. Kemp R. Niederpruem D. Live intercellular nuclear migration patterns Arch. Snider P. Ross I. Swiezynski K.
Milgrim C. Nachman B. Schuren F. Wessels J. Koltin Y. Flexer A. Cell Sci. Behaviour and fate of multi-karyotic hyphae Arch. Raudaskoski M. Hintz W. Anderson J. Horgen P.
Kamada T. Hirai K. Fujii M. Lange V. Flora , , — May G. Taylor J. Giesy R. Jersild R. Mishkin S. Marchant R. Mayfield J. Oakley B. Morris N. Omerod W. Francis S. Margulis L. Mao W. Yli-Mattila T. Response to nocodazole in a sensitive and a tolerant strain of the homobasidiomycete Schizophyllum commune Eur. Cell Biol. Russo P. Juuti J. Salo V.
Niini S. Virtanen I. Stamberg J. Tamarkin A. Boyd D. Bawnik N. Berry D. Saleh F. Meinhardt F. Monokaryotic and dikaryotic fruiting in Schizophyllum commune Curr. Horton J. Loftus M. Foster L. Springer J. Madelin M. Morimoto N. Oda Y. Viitanen H. Ruiters M. Sietsma J.
Rast D. Tan K. Epton H. Radu M. Steinlauf R. Hoge J. Moore D. Elhiti M. Butler R. Mulder G. Salonen M. Rayner A. Kothe E. Scheer J. Constable also thinks the work could have more direct applications. In pathogenic fungi that infect crops, one mating type is often particularly destructive, and the genes that determine that type may be linked to, say, its virulent resistance to antifungals.
Understanding why these traits coexist might help with controlling or preventing blights. But sometimes the nicest works come from these types of inspirations.
Reprinted with permission from Quanta Magazine , an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences. Jordana Cepelewicz is a science writer based in New York City.
Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital.
0コメント