Chitinase modifying proteins from phylogenetically distinct lineages of Brassica pathogens

Authors: Naumann, Todd; Wicklow, Donald

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2013
Publication Date: 4/1/2013
Citation: Naumann, T.A., Wicklow, D.T. 2013. Chitinase modifying proteins from phylogenetically distinct lineages of Brassica pathogens. Physiological and Molecular Plant Pathology. 82:1-9.

Interpretive Summary: Fungi cause devastating economic losses for US food producers by causing plant disease. These fungi also threaten human health by producing harmful toxins that contaminate the food supply. Previously, we identified a plant defense protein in the cabbage family that is inactivated by a specific fungal protein, a fungalysin protease. In this research, we demonstrated that six fungal pathogens of cabbage family plants-which cause crop losses to producers of canola, broccoli, cauliflower, kale, kohlrabi, bok choy, turnip, radishes, and watercress-produce this protease. This finding is important because it identifies a fungal protein that can be targeted by plant breeders and genetic engineers to develop plant varieties with improved disease resistance to multiple pathogens.

Technical Abstract: Chitinase modifying proteins (CMPs) are secreted fungal proteases that truncate specific plant class IV chitinases by cleaving peptide bonds in their amino termini. We recently identified a CMP from the Zea mays (maize) pathogen Fusarium verticillioides and found that it is a member of the fungalysin class of proteases. We also found that Alternaria brassicae, a pathogen of the mustard plant family Brassicaceae, secretes a protease with the same activity. To determine how common fungalysin CMP activity is among fungal pathogens of Brassicaceae plants, we obtained 20 isolates including ten fungal species and tested them for activity. Each fungal isolate was grown saprotrophically on maize and canola seeds. Secreted fungal proteins were extracted from cultures and incubated with three purified plant chitinases: maize ChitA and ChitB, and Arabidopsis thaliana AtchitIV3. We found that fungalysin CMPs were secreted by fungal pathogens distributed among 6 families in three major Ascomycota classes (Dothideomycetes, Leotiomycetes, and Sordariomycetes). Three fungal species that did not secrete fungalysin CMP activity secreted other CMPs that truncated maize ChitA and ChitB by cleaving at different locations, while AtchitIV3 was only susceptible to truncation by fungalysin CMPs. The only fungi that did not secrete CMPs were isolates from the fungal genus Mycosphaerella. These results show that CMPs are commonly secreted by fungal pathogens of Brassicaceae and suggest that interfering with fungalysin CMP activity may improve plant resistance to multiple fungal diseases.