Cla4 PAK-like kinase is required for pathogenesis, asexual/sexual development and polarized growth in Bipolaris...

PAK (p21-activated protein kinases)-like kinases are master regulators of development and morphogenesis, which were conserved among eukaryotes, including fungi. In budding yeast, two types of PAK-like kinases, Ste20 and Cla4 have distinct but shared roles in the regulation of pseudohyphal development, budding and mating. In this study, to examine the broad functions of PAK-like kinases in growth, pathogenicity and asexual/sexual reproduction in filamentous fungi, we identified and characterized two PAK-like kinases, Ste20 and Cla4 in Bipolaris maydis. A single mutant of both Ste20 and Cla4 gene was viable, while the double mutant was not available, possibly because of lethality. In growth, conidiation, and pathogenicity, Δste20 strains showed phenotypes similar to those of the wild-type, while Δcla4 strains showed severely defected phenotypes. In this study, we also clarified that Ste20 is partially involved in pseudothecium development but is dispensable for maternity, while Cla4 is essential for maternal pseudothecium development and also involve in ascospore development in paternal pseudothecium. Fluorescent microscopy visualized the disorder in cell polarity at the hyphal tip in Δcla4. These results suggested that not Ste20 but Cla4 is a master regulator of growth, pathogenicity and asexual/sexual development in B. maydis. In addition, we successfully visualized alternation of branching pattern and distribution of Spitzenkörper at the hyphal tip in Δcla4 strains.