Binding of the <i>Magnaporthe oryzae</i> Chitinase MoChia1 by a Rice Tetratricopeptide Repeat Protein Allows Free Chitin to Trigger Immune Responses

Abstract

To defend against pathogens, plants have developed complex immune systems, including plasma membrane receptors that recognize pathogen-associated molecular patterns, such as chitin from fungal cell walls, and mount a defense response. Here, we identify a chitinase, MoChia1 (<i>Magnaporthe oryzae</i> chitinase 1), secreted by <i>M. oryzae</i>, a fungal pathogen of rice (<i>Oryza sativa</i>). MoChia1 can trigger plant defense responses, and expression of <i>MoChia1</i> under an inducible promoter in rice enhances its resistance to <i>M. oryzae</i> MoChia1 is a functional chitinase required for <i>M. oryzae</i> growth and development; knocking out <i>MoChia1</i> significantly reduced the virulence of the fungus, and we found that MoChia1 binds chitin to suppress the chitin-triggered plant immune response. However, the rice tetratricopeptide repeat protein OsTPR1 interacts with MoChia1 in the rice apoplast. OsTPR1 competitively binds MoChia1, thereby allowing the accumulation of free chitin and re-establishing the immune response. Overexpressing <i>OsTPR1</i> in rice plants resulted in elevated levels of reactive oxygen species during <i>M. oryzae</i> infection. Our data demonstrate that rice plants not only recognize MoChia1, but also use OsTPR to counteract the function of this fungal chitinase and regain immunity.