AbaA and WetA govern distinct stages of Aspergillus fumigatus development

Abstract

The opportunistic human pathogen Aspergillus fumigatus produces a massive number of asexual spores (conidia) as the primary means of dispersal, survival, genome protection and infection of hosts. In this report, we investigate the functions of two developmental regulators, AfuAbaA and AfuWetA, in A. fumigatus. The AfuabaA gene is predicted to encode an ATTS/TEA DNA-binding domain protein and is activated by AfuBrlA during the middle stage of A. fumigatus asexual development (conidiation). The deletion of AfuabaA results in the formation of aberrant conidiophores exhibiting reiterated cylinder-like terminal cells lacking spores. Furthermore, the absence of AfuabaA causes delayed autolysis and cell death, whereas the overexpression of AfuabaA accelerates these processes, indicating an additional role for AfuAbaA. The AfuwetA gene is sequentially activated by AfuAbaA in the late phase of conidiation. The deletion of AfuwetA causes the formation of defective spore walls and a lack of trehalose biogenesis, leading to a rapid loss of spore viability and reduced tolerance to various stresses. This is the first report to demonstrate that WetA is essential for trehalose biogenesis in conidia. Moreover, the absence of AfuwetA causes delayed germ-tube formation and reduced hyphal branching, suggesting a role of AfuWetA in the early phase of fungal growth. A genetic model depicting the regulation of conidiation in A. fumigatus is proposed.

WetA Is Required for Conidiogenesis and Conidium Maturation in the Ascomycete Fungus Fusarium graminearum

“…Previous TEM observations demonstrated that in A. nidulans wetA mutants, the conidium wall is continuous with the innermost layer of the phialide wall (72). Conidia have been shown to be interconnected (5). Similarly, in FgwetA deletion mutants, conidia were not separated and were longer than those from the wild-type strain.…”

“…A. nidulans wetA mutation led to altered cell wall composition and reduced trehalose accumulation (5,72), whereas these phenotypes were normal in the F. graminearum wetA deletion mutant. According to recently proposed models representing patterns of gene evolution for regulators of conidiation, conidiation-related genes are categorized into gene groups that are functionally conserved across fungi, unique to a particular fungal clade, or functionally differentiated with the same biochemical function.…”

“…Abnormal conidial phenotypes in an A. nidulans wetA mutant have been shown to result from altered cell wall composition and reduced trehalose accumulation (5,72). However, the cell wall structures and trehalose levels did not differ between conidia from the F. graminearum wild-type and wetA deletion mutant strains.…”

“…3C and D). Because trehalose is known to be required for spore viability and stress resistance in aspergilli, such as A. nidulans and A. fumigatus, and because wetA is required for trehalose production in A. fumigatus (5,18,68), we measured trehalose production in each strain. All of the strains produced similar levels of trehalose per conidium (see Fig.…”

“…Decades of A. nidulans research have revealed the genetic and biochemical pathways for asexual sporulation, which have been summarized in several reviews (1)(2)(3)(4). Studies have also dissected the molecular mechanisms of conidiogenesis in Aspergillus and Penicillium species, which are evolutionarily related to A. nidulans (5)(6)(7)(8)(9)(10)(11)(12). These reverse genetic studies analyzed well-known regulators of conidiogenesis, such as the fluffy genes, which are activators of the central development pathway genes brlA, abaA, and wetA (2,4,(13)(14)(15)(16).…”