Antifungal activity of rice Pex5p, a receptor for peroxisomal matrix proteins

We have purified a novel antifungal protein from blast fungus (Magnaporthe grisea)-treated rice leaves using consecutive chromatographies on CM-Sepharose ion-change, Affi-gel blue, and HPLC gel filtration columns. We determined the N-terminal peptide sequence of the purified protein and subjected it to the NCBI/BLAST database and found the protein to be a partial fragment of the peroxisomal receptor protein in rice (OsPex5p). After cloning two cDNAs encoding OsPEX5L and OsPEX5S genes that are splice variants of OsPEX5 from a rice leaf cDNA library, we investigated their antifungal properties. The recombinant proteins were expressed in Escherichia coli and found to significantly inhibit cell growth of various pathogenic fungal strains. mRNA expression of the OsPEX5L gene was induced by diverse external stresses such as rice blast fungus, fungal elicitor, and other signaling molecules including H2O2, abscisic acid, jasmonic acid, and salicylic acid. These results suggest that the peroxisomal receptor protein, OsPex5p, plays a critical role in the rice defense system against diverse external stresses including fungal pathogenic attack.