The Control of Sexual Morphogenesis in the Ascomycotina

Abstract

Summary (1) A series of factors controls sexual morphogenesis in the Ascomycotina, a process involving the formation of novel structures such as ascocarps (fruit bodies) and asci (sacs containing spores) during sexual reproduction. (2) Environmental and genetic factors must be correct before Ascomycetes may sexually reproduce. Compatibility in many heterothallic species is under polygenic control, with the mating type loci and also other genetic factors determining the productivity of sexual crosses. (3) Classical genetic studies have shown that sexual morphogenesis involves the expression of a series of developmentally regulated genes, and this has been confirmed by recent molecular studies which have demonstrated changes in patterns of mRNA and protein synthesis during ascocarp formation. (4) Hyphal differentiation leading to the formation of mature fruit bodies occurs in response to a series of signals, which include various physical and chemical factors. (5) Chemical sex factors have been identified which are believed to have important regulatory or nutritional roles in sexual morphogenesis. These include the following. (a) Diffusible sex hormones which may regulate developmental switching between asexual and sexual modes of reproduction, including (i) pheromones involved with the induction of gametangia and gamete attraction, and (ii) sex morphogens involved with triggering particular stages of fruit body formation. (b) Sexual growth substances which are required as nutrients, and may be precursors for the production of sex hormones, or metabolites used in the synthesis of novel sexual structures. Most of these sex factors are lipids. (6) Certain sex morphogens and sexual growth substances have been shown to exhibit activity in a variety of fungal species, suggesting that fungi of related phylogenetic descent may utilize similar metabolites or signalling factors during sexual reproduction. (7) Phenoloxidase enzymes may catalyse hyphal aggregation in developing fruit bodies. (8) Initial stages of ascocarp development may occur independently of the events of the sexual cycle. However, a link(s) with the functional ascogenous hyphae is needed for the formation of morphologically mature ascocarps. (9) Suitable environmental conditions are sufficient to trigger sexual morphogenesis in homothallic Ascomycetes. However, an extra level of control is present in heterothallic species, with a compatible partner required to complete sexual reproduction. This may be partly because novel regulatory products, formed by the combined action of the mating type loci of different partners, are required for further ascocarp development. (10) Further research is required to identify more fungal chemical sex factors and to determine the role of environmental stress in controlling sexual morphogenesis, and how this may be related to temporal patterns in the expression of mating type genes.

Tagging target genes of the MAT1-2-1 transcription factor in Fusarium verticillioides (Gibberella fujikuroi MP-A)

“…This process needs molecular communication between mating partners, followed by finely organized morphogenetic changes, regulated by a number of genes that are affected by either intrinsic and/or environmental stimuli, like age of the culture, temperature, nutrient status or light. Early studies (Dyer et al 1992) suggested that sexual morphogenesis in fungi is under polygenic control and several genes involved in sexual communication have already been characterized in detail (Shen et al 1999;Vallim et al 2000; Pö ggeler and Kü ck 2001; Kim et al 2002;Turina et al 2003;Kim and Borkovich 2004). Nevertheless the molecular mechanisms of this series of events are still not fully understood (Coppin et al 1997;Kronstadt and Staben 1997;Shiu and Glass 2000;Trail et al 2003).…”

A Multiplex PCR Test for Determination of Mating Type Applied to the Plant Pathogens Tapesia yallundae and Tapesia acuformis

“…These may be designated MAT-1 and MAT-2, A and a, or plus "ϩ" and minus "Ϫ" (Dyer et al, 1992). Compatibility is governed by the presence of mating-type genes and progress has been made in cloning these genes from certain ascomycete species.…”

Specific boundaries between the causal agents of the soybean stem canker

“…It has been proposed that the incompatibility reaction may limit the spread of harmful cytoplasmic or nuclear elements (Caten, 1972), and prevent resource plundering (Debets & Griffiths, 1998). It has also been suggested that vegetative incompatibility may promote the initiation of sexual reproduction in some species as a result of non-self recognition (Dyer et al, 1992). Individuals that share the same heterokaryon or vegetative incompatibility loci can fuse to form a heterokaryon and are then considered to belong to the same vegetative compatible group (Glass et al, 2000).…”