Fungus cell biology in 3-D

The British Mycological Society has a new special issue of its Fungal Biology Reviews (March 2011) which contains a series of plenary papers from the Ninth International Mycological Congress held in Edinburgh in August of 2010. (These conferences have been held since 1971, usually every four years.) This conference had five major themes:

  • Cell biology, biochemistry and physiology
  • Environment, ecology and interactions
  • Evolution, biodiversity and systematics
  • Pathogenesis and disease control; and
  • Genomics, genetics and molecular biology

Among the speakers, all of whom submitted papers for this issue, were Gero Steinberg (University of Exeter), David Hibbett (Clark University), Joseph Heitman (Duke University), Nicholas J. Talbot (University of Exeter), Alastair Fitterand (York University) and Nancy Keller (University of Wisconsin at Madison). Elsevier, which publishes the journal, has made the entire issue freely available on ScienceDirect, which will continue to host it through the end of the month (according to the ScienceDirect website; the Eurekalert press release, however, says that it will remain available until 2012). The papers range among such topics as fungal pathogens, mycorrhizal symbiosis between fungi and roots of vascular plants, and the possible origin of fungal secondary metabolites genes from spore pigments.

The most interesting of the papers, however, is Gero Steinberg & Martin Schuster, “The dynamic fungal cell,” 25 Fungal Biology Reviews 14-37 (March 2011). The paper is a detailed overview of the organization and motility of cellular structures in a fungal cell. The prototype they use is the corn smut virus (Ustilago maydis), a pathogen of the cereal grain maize (Zea mays). This fungus is also known as huitlacoche in Mexico, where it is sold and consumed as food. The fungus is a model species for laboratory work since it is easily genetically modified and its entire genome has been described. It exists in two forms: A yeast-like single-cell form (sporidium) which reproduces asexually by budding; and a hyphal growth form which it assumes when two compatible mating sporidia meet, fuse and send out hyphae to enter the host plant.

Figure 1 of the Steinberg and Schuster paper. Click to enlarge.

What makes the paper especially important is that it includes 76 videos which show the 3-dimensional organization and the behaviour of the cytoskeleton and major components of the fungal cells. The authors used fluorescent marker proteins to label sub-cellular structures and compartments of the cell. Among the videos are ones illustrating the microtubule organization of the cell, microtubule movement, microtubule organization and movement during mitosis, the F-actin “cables” and patches in the hyphae, the various “motors” which drive cell movement, the endoplasmic reticulum, mitochondria, vacuoles, and so forth. In short, it shows all the organelles, motors and the filaments of the cytoskeleton in a living fungal cell.

The press release which announced the paper claims that the videos “comprise the most comprehensive collection of fungal cell biology movies ever published.”

The paper draws two conclusions from the videos. First, “most organelles are evenly scattered and they seem to perform their cellular function along the whole length of the hyphal cell.” The authors concede, however, that the method of communication between one end of the cell to the other is poorly understood. Second, different organelle have different degrees of motility with early endosomes, for example, continuously moving, while mitochondria, on the other hand, are mostly stationary. They conclude that a complete understanding of the biology of the fungal cell would require something to “bridge between the questions ‘how do organelles move?’ and ‘why do organelles move?'”

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