AbaA Regulates Conidiogenesis in the Ascomycete Fungus Fusarium graminearum

Abstract

Fusarium graminearum (teleomorph Gibberella zeae) is a prominent pathogen that infects major cereal crops such as wheat, barley, and maize. Both sexual (ascospores) and asexual (conidia) spores are produced in F. graminearum. Since conidia are responsible for secondary infection in disease development, our objective of the present study was to reveal the molecular mechanisms underlying conidiogenesis in F. graminearum based on the framework previously described in Aspergillus nidulans. In this study, we firstly identified and functionally characterized the ortholog of AbaA, which is involved in differentiation from vegetative hyphae to conidia and known to be absent in F. graminearum. Deletion of abaA did not affect vegetative growth, sexual development, or virulence, but conidium production was completely abolished and thin hyphae grew from abnormally shaped phialides in abaA deletion mutants. Overexpression of abaA resulted in pleiotropic defects such as impaired sexual and asexual development, retarded conidium germination, and reduced trichothecene production. AbaA localized to the nuclei of phialides and terminal cells of mature conidia. Successful interspecies complementation using A. nidulans AbaA and the conserved AbaA-WetA pathway demonstrated that the molecular mechanisms responsible for AbaA activity are conserved in F. graminearum as they are in A. nidulans. Results from RNA-sequencing analysis suggest that AbaA plays a pivotal role in conidiation by regulating cell cycle pathways and other conidiation-related genes. Thus, the conserved roles of the AbaA ortholog in both A. nidulans and F. graminearum give new insight into the genetics of conidiation in filamentous fungi.

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

“…To analyze the genetic relationship between abaA and wetA in F. graminearum, we generated strains HK154 (⌬wetA::gen ⌬abaA::gen) and HK155 (⌬wetA::gen abaA::gen-P ef1␣ -abaA) by outcrossing HK148 with the ⌬abaA mutant and HK148 with AbaA-OE, respectively. As seen previously, the abaA deletion mutants produced immature phialides with abnormal morphology (41), which germinated and became thin hyphae. The AbaA-OE mutant produced abacus-like phialides and conidia (Fig.…”

“…We found that AbaA is important for phialide formation and function and that abaA overexpression causes pleiotropic phenotypes in F. graminearum. We also demonstrated that the AbaA-WetA pathway of A. nidulans is conserved in F. graminearum (41).…”

“…Genetic relationship between abaA and wetA. In our previous study, we predicted that the AbaA-WetA pathway is important for conidiation in F. graminearum (41). To analyze the genetic relationship between abaA and wetA in F. graminearum, we generated strains HK154 (⌬wetA::gen ⌬abaA::gen) and HK155 (⌬wetA::gen abaA::gen-P ef1␣ -abaA) by outcrossing HK148 with the ⌬abaA mutant and HK148 with AbaA-OE, respectively.…”

“…Our work was particularly meaningful because we deepened the understanding of pathogenicity mechanisms by connecting well-known cellular processes with virulence in F. graminearum. In addition, we characterized the abaA ortholog, which was previously thought to be absent from F. graminearum (41). We found that AbaA is important for phialide formation and function and that abaA overexpression causes pleiotropic phenotypes in F. graminearum.…”

“…Knockout mutants of these genes were found to be pleiotropic and defective in sexual reproduction, vegetative growth, virulence, and conidiation. To our knowledge, there are only five F. graminearum transcription factors that specifically regulate conidium production (34,41,42). Since few conidiationspecific genes are known and there has been no systematic study of conidiation in F. graminearum, scant information regarding the molecular mechanism of conidium production is available.…”