Neurospora crassa is a central organism in the history of twentieth-century genetics, biochemistry and molecular biology. Here, we report a high-quality draft sequence of the N. crassa genome. The approximately 40-megabase genome encodes about 10,000 protein-coding genes-more than twice as many as in the fission yeast Schizosaccharomyces pombe and only about 25% fewer than in the fruitfly Drosophila melanogaster. Analysis of the gene set yields insights into unexpected aspects of Neurospora biology including the identification of genes potentially associated with red light photobiology, genes implicated in secondary metabolism, and important differences in Ca(2+) signalling as compared with plants and animals. Neurospora possesses the widest array of genome defence mechanisms known for any eukaryotic organism, including a process unique to fungi called repeat-induced point mutation (RIP). Genome analysis suggests that RIP has had a profound impact on genome evolution, greatly slowing the creation of new genes through genomic duplication and resulting in a genome with an unusually low proportion of closely related genes

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Proteins in the Rho family are small monomeric GTPases primarily involved in polarization, control of cell division, and reorganization of cytoskeletal elements. Phylogenetic analysis of predicted fungal Rho proteins suggests that a new Rho-type GTPase family, whose founding member is Rho4 from the archiascomycete Schizosaccharomyces pombe, is involved in septation. S. pombe rho4⌬ mutants have multiple, abnormal septa. In contrast to S. pombe rho4⌬ mutants, we show that strains containing rho-4 loss-of-function mutations in the filamentous fungus Neurospora crassa lead to a loss of septation. Epitope-tagged RHO-4 localized to septa and to the plasma membrane. In other fungi, the steps required for septation include formin, septin, and actin localization followed by cell wall synthesis and the completion of septation. rho-4 mutants were unable to form actin rings, showing that RHO-4 is required for actin ring formation. Characterization of strains containing activated alleles of rho-4 showed that RHO-4-GTP is likely to initiate new septum formation in N. crassa.In many organisms, the purpose of cytokinesis is to couple the process of making a new cell with the replication of the nucleus. In eukaryotes, this can be accomplished by positioning the division plane according to the location of the spindle or by moving mitotic machinery to an already determined division plane (15). Most eukaryotes tightly couple cell division with replication of the nucleus, making cell division essential for viability. For example, Saccharomyces cerevisiae moves the mitotic machinery to the division plane specified by "landmark proteins," which remain at the bud scar (10). In contrast, the division plane in animal cells is determined by the position of either the spindle midzone (56) or astral microtubules (38). In filamentous fungi, which grow by apical tip extension to form highly polarized multinucleate cells called hyphae, cytokinesis occurs by the formation of crosswalls or septa. These septa serve to define the boundary between hyphal compartments. However, septal pores maintain cytoplasmic continuity in a colony and allow nuclei and organelles to travel between cells (23). Three observations suggest that filamentous fungi have partially uncoupled septation from mitosis: (i) hyphal compartments are multinucleate, (ii) septation is observed in anucleate compartments of Neurospora crassa ropy mutants (29), and (iii) Ashbya gossypii Agcky1 mutants lack septa but grow at a wildtype rate (53). Thus, the partial uncoupling of cell division from mitosis allows isolation of viable aseptate mutants in filamentous fungi. Septation in filamentous fungi is required for certain developmental processes, such as conidiation (asexual spore production) and protoperithecial (female sexual structure) development (20,37). In addition, septa may serve a structural role in maintaining the tubular shape of hyphae.Septa also act as a scaffold for the Woronin body, a septal plug that stops cytoplasmic leaking after hyphal injury (23,24,48).The process o...

SUMMARYIn plants, as in all eukaryotic organisms, microtubule-and actin-filament based structures play fundamental roles during cell division. In addition to the mitotic spindle, plant cells have evolved a unique cytoskeletal structure that designates a specific division plane before the onset of mitosis via formation of a cortical band of microtubules and actin filaments called the preprophase band. During cytokinesis, a second plantspecific microtubule and actin filament structure called the phragmoplast directs vesicles to create the new cell wall. In response to intrinsic and extrinsic cues, many plant cells form a preprophase band in G 2 , then the preprophase band recruits specific proteins to populate the cortical division site prior to disassembly of the preprophase band in prometaphase. These proteins are thought to act as a spatial reminder that actively guides the phragmoplast towards the cortical division site during cytokinesis. A number of proteins involved in determination and maintenance of the plane of cell division have been identified. Our current understanding of the molecular interactions of these proteins and their regulation of microtubules is incomplete, but advanced imaging techniques and computer simulations have validated some early concepts of division site determination.

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