Chimeric receptor kinases for plant disease resistance engineering in rice

Incompatible interactions between plants and pathogens are characterized by defense responses such as the oxidative burst, hypersensitive cell death, and defense-gene activation. These interactions are often “gene-for-gene” specific. Developing a nonspecific disease resistance strategy is important. We designed chimeric receptors that combined the intracellular domain of the rice receptor kinase Xa21 conferring bacterial blight resistance with the extracellular ligand-binding domains from other proteins. Cell death and an oxidative burst were observed in cell lines expressing the Xa21 gene when inoculated with an avirulent strain of Xanthomonas oryzae pv. oryzae (Xoo) but not with a virulent strain or in the wild-type cell line. Transcription of two defense-related genes, RCH10 and PAL, was induced, whereas OsCatB was down-regulated in the incompatible interaction. One of the chimeric receptors, NRG1 (novel receptor gene), which consisted of the extracellular and transmembrane domains of the Arabidopsis brassinosteroid receptor (BRI1) and the XA21 kinase domain, was constitutively expressed in rice cell lines. These cell lines displayed cell death, RCH10 and PAL activation, and OsCatB suppression when treated with the ligand brassinolide (BL), as compared with wild-type and mutant controls. Another chimeric receptor-like kinase, NRG6, which combined the extracellular chitin-binding (Hevein) domain of rice chitinase with the XA21 transmembrane and kinase domains, also showed cell death, an oxidative burst, and defense-related gene activation/suppression in constitutive-expression cell lines after treatment with chitin. The NRG1 and NRG6 plants exhibited dwarfism and partial disease resistance to Xoo. Our work provides a new approach for the design of novel signaling genes controlling plant disease resistance and development, and for the discovery of ligands for leucine-rich-repeat receptor kinases.