Recognition and Analysis of a Host-Targeting Motif in the Genome of Fungus Magnaporthe Grisea

A highly conservative host-targeting motif composed of 4 amino acid residues, namely, RxLx was reported to be present only in virulence proteins of malarial parasites (Plasmodium species) and the oomycete avirulence(Avr) protein of Phytophthora. In the present study, we analyzed the secretory proteins of the rice blast fungus Magnaporthe grisea that were predicted by bioinformatics and comparative genomic tools to determine whether the RxLx motif is present in the secretory proteins. In 297 of 1270 secretory proteins, the RxLx motif was detected within a region of 100 amino acids downstream the N-terminal signal peptide cleavage sites. A comparison with the PEDANT database revealed that RxLx motif-containing proteins included enzymes for the degradation of plant cell wall components such as cellulose, endoxylanase, endoglucanase and cutinase hydrolase for degradation of plant cell membrane and cellular contents, this suggests that the RxLx motif-containing proteins probably functioned as virulence proteins and were primarily involved in interaction between the rice blast fungus and host cells. So, our results support the idea that the host -targeting motif (HTM) is a conserved transport machinery, which imply that divergent eukaryotic pathogens might share common mechanisms of pathogenicity. This research will provide useful materials to elucidate whether similar or distinct pathogenic secretion signlals in different eukaryotic pathogens and can be helpful to validate predicted function of the HTM in vivo.