Fungi Life Cycle

To give the life cycle of fungi will draw the growth cycle on Ascomycete Yeast (Saccharomyces Cerevisiae).
S.cerevisiae is an extremely well studied organism, with a clearly defined and experimentally manipulable life cycle. The life cycle of yeast involves mitotically propagating haploid forms of two distinct mating types, and a diploid form that can either grow vegetatively or be induced into a meiotic developmental path way through manipulation of the nutrient conditions of the growth medium. The cellular pathways regulating processes such as mitotic proliferation, cell recognition and mating, meiosis and sporulation have been extensinvely studied on a molecular level, and are generally well understood.

Mitotic growth of yeast cells involves budding. During this process growth of the cell is directed to a specific location on the surface of the mother cell, and a new cell is formed somewhat like blowing up a balloon through a hole in the mother cell, implicating both the actin and microtubule based cytoskeletal networks, and is tightly coordinated with the cell cycle. This coordination ensures that the doughter cell receives a complete copy of the genetic material. Both haploid and diploid cells divide by the budding process, although there are subtle differences in the choice of the sites of bud emergence between haploids and diploids. In addition, some diploid cells can also modify the coordination of the cell cycle and polarized growth to switch to a pseudohyphal growth mode. In this growth pattern individual cells are more elongated, and the budding pattern leads to the formation of chains of cells rather than compact colonies characteristic of the true budding mode.

Genetic analysis is highly developed in S. cerevisiae, when vegetatively growing haploid cells of opposite matting types are brought into proximity, they communicate to each other by diffusible pheromones, synchronize their cell cycles, conjugate and then fuse their nuclei to create non-mating, meiosis proficient diploids. These diploids can be identified visually in their initial zygote form, and separated from the haploids by micromanipulation, or identified selectively because they contain a pattern of genetic traits not possessed by either haploid parent.

Under rich condition such haploid cells propagate vegetatively, but under conditions of nitrogen and fermentable carbon limitation the diploid cells are induced to initiate meiosis and sporulation. The ability to propagate the diploid allows the amplification of the initial mating product, and provides an essentially unlimited source of potential meiotic events from single mating.