Innate immunity can be rapidly activated to defend a host plant against a microbial pathogen. The rice protein XA21, which is thought to be a cell surface–located receptor with a kinase domain, activates the plant’s defenses in response to infection by certain strains of Xanthomonas bacteria. Lee et al. have now identified the bacterial gene that encodes the protein, AvrXA21, to which the plant receptor XA21 responds. The 194–amino acid protein needs to be secreted and sulfated to trigger the rice plant defense responses. Similarities exist between the receptor XA21 and other immune response receptors in both plants and animals.
S.-W. Lee, S.-W. Han, M. Sririyanum, C.-J. Park, Y.-S. Seo, P. C. Ronald, A type I–secreted, sulfated peptide triggers XA21-mediated innate immunity. Science 326, 850–853 (2009). [Abstract] [Full Text]