PROTECTIVE ENDOPHYTES OF MAIZE THAT INHIBIT FUNGAL PATHOGENS AND REDUCE MYCOTOXIN CONTAMINATION
Location: Bacterial Foodborne Pathogens & Mycology Research Unit
Title: Identification of a chitinase modifying protein from Fusarium verticillioides: truncation of a host resistance protein by a fungalysin metalloprotease
Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 2011
Publication Date: October 14, 2011
Citation: Naumann, T.A., Wicklow, D.T., Price, N.P. 2011. Identification of a chitinase modifying protein from Fusarium verticillioides: Truncation of a host resistance protein by a fungalysin metalloprotease. Journal of Biological Chemistry. 286(41):35358-35366.
Interpretive Summary: Mycotoxins are potentially harmful contaminants of corn and other crops. Fusarium fungi are major producers of mycotoxins in corn, and some Fusarium mycotoxins are linked to cancer and other diseases of humans, pets, and livestock. Finding ways to improve natural plant defenses is critical to reducing Fusarium infections and mycotoxin contamination in corn and other crops. However, this requires a greater understanding of the methods employed by Fusarium to overcome plant defenses. In this research, we identified a protein produced by Fusarium that directly interferes with the function of ChitA, a known plant defense protein. We identified the specific part of ChitA that is targeted by this fungal protein, and found that it is also present in similar proteins produced by other plants. This suggests that these fungal proteins may also function in Fusarium diseases of crops like wheat, barley, and rye. This information will be useful to plant breeders and genetic engineers who work to produce maize hybrids that are resistant to Fusarium. This will make the US corn crop both safer, by reducing mycotoxin contamination, and more profitable, by increasing yields.
Chitinase modifying proteins (cmps) are proteases, secreted by fungal pathogens, which truncate the plant class IV chitinases ChitA and ChitB during maize ear rot. Cmp activity has been characterized for Bipolaris zeicola and Stenocarpella maydis, but the identities of the proteases are not known. Here we report that cmps are secreted by multiple species from the genus Fusarium, that Fv-cmp from Fusarium verticillioides is a fungalysin metalloprotease, and that it cleaves within a sequence that is conserved in class IV chitinases. Protein extracts from Fusarium cultures were found to truncate ChitA and ChitB in vitro. Based on this activity, Fv-cmp was purified from F. verticillioides. Amino-terminal sequencing of truncated ChitA and MALDI-TOF analysis of reaction products showed that Fv-cmp is an endoprotease that cleaves a peptide bond on the carboxyl side of the lectin domain. The amino-terminal sequence of purified Fv-cmp was determined and compared with a set of predicted proteins, resulting in its identification as a zinc metalloprotease of the fungalysin family. Recombinant Fv-cmp also truncated ChitA, confirming its identity, but had poor activity, indicating that recombinant protease does not mature efficiently from its propeptide-containing precursor. This is the first report of a fungalysin that targets a non-structural host protein and the first to implicate this class of virulence-related proteases in plant disease.