AUTHOR=Qu Yingmin , Wang Jing , Huang Pengyun , Liu Xiaohong , Lu Jianping , Lin Fu-Cheng 

TITLE=PoRal2 Is Involved in Appressorium Formation and Virulence via Pmk1 MAPK Pathways in the Rice Blast Fungus Pyricularia oryzae

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.702368

DOI=10.3389/fpls.2021.702368

ISSN=1664-462X

ABSTRACT=<p><italic>Pyricularia oryzae</italic> is an important plant pathogenic fungus that can severely damage rice and wheat crops, leading to significant reductions in crop productivity. To penetrate into and invade tissues of its plant host, this fungus relies on an invasive structure known as an appressorium. Appressorium formation is rigorously regulated by the cAMP-PKA and Pmk1 MAPK pathways. Here, we identified PoRal2, a homologous protein of <italic>Schizosaccharomyces pombe</italic> Ral2, and characterized its roles in fungal development and virulence in <italic>P. oryzae</italic>. PoRal2 contains N-terminal kelch repeats and C-terminal BTB domains. PoRal2 is involved in sporulation, aerial hypha and conidiophore differentiation, appressorium formation, plant penetration, and virulence. During appressorium formation, ∆<italic>Poral2</italic> mutants generate appressoria with long germ tubes on hydrophobic surfaces. ∆<italic>Poral2</italic> mutants exhibited a defective response to exogenous cAMP and the activated <italic>RAS2</italic><sup>G18V</sup> on a hydrophilic surface, indicating impairment in the cAMP-PKA or Pmk1 MAPK signaling pathways. Deletion of <italic>PoRAL2</italic> leads to lowered Pmk1 phosphorylation level in the mutant. Moreover, PoRal2 is found to interact with Scd1, Smo1, and Mst50, which are involved in activation of Pmk1. In addition, the expression levels of <italic>MPG1</italic>, <italic>WISH</italic>, and <italic>PDEH</italic> in the cAMP-PKA pathway, <italic>RAS2</italic> in both the cAMP-PKA and Pmk1 MAPK pathways, and melanin biosynthesis genes (<italic>ALB1</italic>, <italic>BUF1</italic>, and <italic>RSY1</italic>) were significantly down-regulated in the ∆<italic>Poral2</italic>. Therefore, PoRal2 is involved in fungal development and virulence by its crosstalk in the cAMP-PKA and Pmk1 MAPK signaling pathways.</p>