Bacterial blight of rice, caused by Xanthomonas oryzae pv. oryzae, is one of the most destructive
bacterial diseases throughout the major rice-growing regions in the world. The rice
disease resistance (R) gene Xa10 confers race-specific
disease resistance to X. oryzae pv. oryzae strains that deliver the corresponding transcription activator-like (
TAL) effector AvrXa10. Upon
bacterial infection, AvrXa10 binds specifically to the effector binding
element in the promoter of the R gene and activates its expression. Xa10 encodes an executor R
protein that triggers hypersensitive response and activates
disease resistance. 'Nipponbare' rice carries two Xa10-like genes in its genome, of which one is the susceptible allele of the Xa23 gene, a Xa10-like
TAL effector-dependent executor R gene isolated recently from 'CBB23' rice. However, the function of the two Xa10-like genes in
disease resistance to X. oryzae pv. oryzae strains has not been investigated. Here, we designated the two Xa10-like genes as Xa10-Ni and Xa23-Ni and characterized their function for
disease resistance to rice bacterial blight. Both Xa10-Ni and Xa23-Ni provided
disease resistance to X. oryzae pv. oryzae strains that deliver the matching artificially designed
TAL effectors (
dTALE). Transgenic rice plants containing Xa10-Ni and Xa23-Ni under the Xa10 promoter provided specific
disease resistance to X. oryzae pv. oryzae strains that deliver AvrXa10. Xa10-Ni and Xa23-Ni knock-out mutants abolished
dTALE-dependent
disease resistance to X. oryzae pv. oryzae. Heterologous expression of Xa10-Ni and Xa23-Ni in Nicotiana benthamiana triggered cell death. The 19-amino-acid residues at the N-terminal regions of XA10 or XA10-Ni are dispensable for their function in inducing cell death in N. benthamiana and the C-terminal regions of XA10, XA10-Ni, and XA23-Ni are interchangeable among each other without affecting their function. Like XA10, both XA10-Ni and XA23-Ni locate to the endoplasmic reticulum (ER) membrane, show self-interaction, and induce ER Ca2+ depletion in leaf cells of N. benthamiana. The results indicate that Xa10-Ni and Xa23-Ni in Nipponbare encode functional executor R
proteins, which induce cell death in both monocotyledonous and dicotyledonous plants and have the potential of being engineered to provide broad-spectrum
disease resistance to plant-pathogenic Xanthomonas spp.