A genetic network of winged-helix transcription factors regulating sexual reproduction in the homothallic fungus Fusarium graminearum

Abstract

Fusarium graminearum is a destructive plant pathogenic fungus causing Fusarium head blight (FHB) on various cereal crops. The infection of this fungus leads to severe yield losses and contamination of mycotoxins, such as trichothecenes and zearalenone, that are harmful to humans and animals. This fungus produces two types of spores through sexual and asexual reproduction. During sexual reproduction, ascospores are produced and discharged from the fruiting bodies perithecia, serving as the primary inocula in the following spring. In plant disease epidemiology, sexual reproduction is crucial in that it increases genetic diversity of population and provides overwintering structures such as perithecia and associated tissues. It has been known that mating-type factors act as master regulators in sexual reproduction, but there is still a limited understanding of the molecular mechanisms underlying sexual developmental stages. Winged-helix transcription factors (TFs) are key regulators of embryogenesis and cell differentiation in higher eukaryotes. In several fungal species, it also has been revealed that they are involved in fungal morphogenesis and development. In F. graminearum, there are 28 putative winged-helix transcription factors. The objectives of this study were i) to determine the roles of winged-helix genes and ii) to figure out their genetic relationship with mating-type genes during the sexual development in this fungus. In this study, nine winged-helix TFs that appeared to be important for sexual reproduction were investigated. Deletion, complementation, and overexpressing mutants were generated, and their phenotypes were analyzed. All deletion mutants were self-sterile and defective in perithecia formation and/or ascospore development. Extensive outcross analyses revealed that, four self-sterile mutants, Δgzwing15, Δgzwing16, Δgzwing20, and Δgzwing27, had both female and male fertilities same as mating-type gene mutants. Moreover, these four genes were expected to have essential roles in sexual reproduction by constructing genetic networks with mating-type genes. The results of this study will contribute to the understanding of molecular genetic regulation of sexual development in fungi.

붉은곰팡이(Fusarium graminearum)는 전 세계적으로 주요작물에 병을 일으켜 경제적 손실을 일으키고 인축에 유해한 곰팡이 독소를 생산하는 중요한 식물병원성 곰팡이이다. 붉은곰팡이는 유성생식을 통해 유전적 다양성을 획득하고 병 전파에 있어 일차전염원으로 작용하는 자낭포자를 생산한다. 유성생식과정에서 Mating-type 유전자가 주요 조절자 역할을 하는 것으로 알려져 있지만, 유성생식과정의 분자생물학적 메커니즘에 대한 연구는 여전히 부족하다. Winged-helix 전사조절인자는 진핵 생물에서 발생 및 세포분화의 주요 조절자이다. 붉은곰팡이는 28개의 winged-helix 전사조절인자를 가지고 있다고 밝혀져 있다. 본 연구에서는 유성생식과정에 관련되어 있을 것으로 추정되는 9개의 전사조절인자의 기능을 조사하고, 유성생식과정에서 mating-type 유전자와의 유전적관계를 분석하였다. Winged-helix 유전자의 결손변이체, 형질복원체, 과발현체를 제작하여 이들의 표현형을 분석하였다. 모든 결손변이체는 유성생식과정에서 결함을 보였다. 또한 outcross를 통해 GzWING15, GzWING16, GzWING20, GzWING27 결손변이체가 mating-type 유전자와 동일하게 female과 male 생식능력을 모두 가지고 있음을 확인하였다. 또한 유성생식과정에서의 전사량 분석을 수행하여 winged helix 유전자와 mating-type 유전자의 관련성을 확인하였다. 본 연구의 결과를 통해 winged helix 유전자가 유성생식과정과 mating-type 유전자에 관련이 있음을 확인하였고, 이들이 유전적 네트워크를 구축하여 유성생식에서 중요한 역할을 할 것이라 추정할 수 있다.