Bacterial blight resistance gene Xa3/Xa26 encoding a leucine-rich repeat (LRR) receptor kinase type protein and belongs to a multiple gene family.Functional analysis of Xa3/Xa26 gene family members in 3 rice cultivars show that RKx can form lesion mimics, when overexpressed and transformed to japonica Mudanjiang 8.The lesions can be formed spontaneously and can propagate from small to large ones, even under sterilized condition.At adult stage, the lesions can be found in leaf blade, leaf sheath and peduncle of panicle.The lesions on leaves of the transgenetic plants were examined using Trypan blue staining and UV-stimulated autofluorescence.The results showed that the lesions were related with cell death.Diaminobenzidin (DAB) and nitroblue tetrazolium (NBT) staining of the leaves with lesion mimics showed that the levels of H2O2 and superoxides were increased.RKx-△k, encoding truncated receptor kinase lacking the kianse domain, when overexpressed in Mudanjiang 8, could not form lesions.The kinase domains of XA3/XA26 and RKx share 85% sequence identity.To study the relationship of downstream reactions triggered by XA3/XA26 and RKx, chimeric genes were constructed and overexpressed in Mudanjiang 8.Plants carrying the chimeric protein, consisted of the LRR domain and transmembrane domain of RKx and the kinase domain of XA3/XA26, formed spontaneously lesions as the RKx-overexpressing plants.These results suggest that the kinase domains of RKx and XA3/XA26 are functional interchangeable.These results also suggest that the signaling pathways triggered by XA3/XA26 and RKx may at least partial overlap.