Microcyle Conidiation in Filamentous Fungi

Abstract

The typical life cycle of filamentous fungi commonly involves asexual sporulation after vegetative growth in response to environmental factors. The production of asexual spores is critical in the life cycle of most filamentous fungi. Normally, conidia are produced from vegetative hyphae (termed mycelia). However, fungal species subjected to stress conditions exhibit an extremely simplified asexual life cycle, in which the conidia that germinate directly generate further conidia, without forming mycelia. This phenomenon has been termed as microcycle conidiation, and to date has been reported in more than 100 fungal species. In this review, first, we present the morphological properties of fungi during microcycle conidiation, and divide microcycle conidiation into four simple categories, even though fungal species exhibit a wide variety of morphological differences during microcycle conidiogenesis. Second, we describe the factors that influence microcycle conidiation in various fungal species, and present recent genetic studies that have identified the genes responsible for this process. Finally, we discuss the biological meaning and application of microcycle conidiation.

Fluorescent markers of various organelles in the wheat pathogen Zymoseptoria tritici

“…The even distribution at the cell periphery is in agreement with its proposed localization in the plasma membrane in Aspergillus nidulans ( Taheri-Talesh et al, 2008 ). Using eGFP-ZtSso1 confirmed previous observations that Z. tritici macropycnidiospores are multi-cellular ( Steinberg, 2015 ) and grow by lateral “budding”, a process named “microcycle conidiation” ( Jung et al, 2014 ; Fig.4 D). The localization in the plasma membrane was further confirmed by co-visualization of eGFP-ZtSso1 and the lipophilic probe FM4-64 ( Fig.4 E), which enters the fungal plasma membrane before uptake into the cell ( Fischer-Parton et al, 2000 , Wedlich-Söldner et al, 2000 ).…”

Epiphytic and endophytic colonisation of tomato plants by the entomopathogenic fungus Beauveria bassiana strain GHA

“…In addition, conidia germinated, and the germ tubes directly produced a conidiophore and phialides, which formed two or three conidia (Figure 1(e)). This phenomenon, termed microcycle conidiation, is well known in fungi (Hanlin 1994;Jung et al 2014).…”

The microcyclic conidial stage of Coniochaeta pulveracea and its effect on selected biological interactions

“…The hyphae were characterized by cylindrical terminal phialides (a), as well as by discreet intercalary phialides with very short necks (b) and slightly flaring collarettes (c). In some cases evidence of microcycle conidiation, as described by Jung et al (2014) was observed (d). c Light micrographs of C. pulveracea CBS110471 in submerged cultures, prepared with yeast peptone dextrose broth, showing hyphal growth, as well as yeastlike microcycle conidiation (e) for a number of fungi capable of microcycle conidiation (Pažout and Schröder 1988;Hanlin 1994;Boualem et al 2014;Jung et al 2014).…”

“…In some cases evidence of microcycle conidiation, as described by Jung et al (2014) was observed (d). c Light micrographs of C. pulveracea CBS110471 in submerged cultures, prepared with yeast peptone dextrose broth, showing hyphal growth, as well as yeastlike microcycle conidiation (e) for a number of fungi capable of microcycle conidiation (Pažout and Schröder 1988;Hanlin 1994;Boualem et al 2014;Jung et al 2014). It must be noted, however, that such transfer to a liquid medium, and the subsequent switch to microcycle conidiation as recorded in literature, was usually accompanied by other changes in the physico-chemical characteristics of the medium such as shifts in temperature, pH or nutrient composition.…”

“…Inhibitors of mRNA, such as α-amanitin, were found to suppress the process of microcycle conidiation by Cercospora zeae-maydis. In some Fusarium species, including Fusarium verticillioides and Fusarium graminearum, deletion of specific genes may result in microcycle conidiation (Lapaire and Dunkle 2003;Jung et al 2014). Zhang and Xia (2008) used suppression subtractive hybridization to identify genes related to microcycle conidiation.…”