Endocytosis is an essential cellular process in eukaryotic cells that involves 
concordant functions of clathrin and adaptor proteins, various protein and lipid 
kinases, phosphatases and the actin cytoskeleton. In Saccharomyces cerevisiae, 
Ark1p is a member of the serine/threonine protein kinase (SPK) family that 
affects profoundly the organization of the cortical actin cytoskeleton. To study 
the function of MoArk1, an Ark1p homologue identified in Magnaporthe oryzae, we 
disrupted the MoARK1 gene and characterized the ΔMoark1 mutant strain. The 
ΔMoark1 mutant exhibited various defects ranging from mycelial growth and 
conidial formation to appressorium-mediated host infection. The ΔMoark1 mutant 
also exhibited decreased appressorium turgor pressure and attenuated virulence 
on rice and barley. In addition, the ΔMoark1 mutant displayed defects in 
endocytosis and formation of the Spitzenkörper, and was hyposensitive to 
exogenous oxidative stress. Moreover, a MoArk1-green fluorescent protein 
(MoArk1-GFP) fusion protein showed an actin-like localization pattern by 
localizing to the apical regions of hyphae. This pattern of localization 
appeared to be regulated by the N-ethylmaleimide-sensitive factor attachment 
protein receptor (SNARE) proteins MoSec22 and MoVam7. Finally, detailed analysis 
revealed that the proline-rich region within the MoArk1 serine/threonine kinase 
(S_TKc) domain was critical for endocytosis, subcellular localization and 
pathogenicity. These results collectively suggest that MoArk1 exhibits conserved 
functions in endocytosis and actin cytoskeleton organization, which may underlie 
growth, cell wall integrity and virulence of the fungus.