Abstract
BackgroundRice Xa3/Xa26 disease-resistance gene encodes a leucine-rich repeat (LRR) receptor kinase-type protein against Xanthomonas oryzae pv. oryzae (Xoo) and belongs to a multigene family. However, the functions of most genes in this family are unknown.ResultsHere we report that two orthologs of this family, the NRKe from rice variety Nipponbare and 9RKe from variety 93-11 at the RKe locus, have similar functions although they encode different proteins. This pair of orthologs could not mediate resistance to Xoo, but they were transcriptionally induced by raised temperature. Transcriptional activation of NRKe or 9RKe resulted in the formation of temperature-sensitive lesion mimics, which were spots of dead cells associated with accumulation of superoxides, in different organs of the transgenic plants. These plants were more sensitive to high temperature shock than wild-type controls. Transgenic plants carrying a chimeric protein consisting of the LRR domain of NRKe and the kinase domain of Xa3/Xa26 developed the same lesion mimics as the NRKe-transgenic plants, whereas transgenic plants carrying another chimeric protein consisting of the LRR domain of Xa3/Xa26 and the kinase domain of NRKe were free of lesion mimic. All the transgenic plants carrying a chimeric protein were susceptible to Xoo.ConclusionThese results suggest that the RKe locus is involved in rice response to raised temperature. The LRR domain of RKe protein appears to be important to sense increased temperature. The RKe-involved temperature-related pathway and Xa3/Xa26-mediated disease-resistance pathway may partially overlap.
Highlights
Rice Xa3/Xa26 disease-resistance gene encodes a leucine-rich repeat (LRR) receptor kinase-type protein against Xanthomonas oryzae pv. oryzae (Xoo) and belongs to a multigene family
Overexpression of RKe resulted in the formation of lesion mimics in rice plants The paralog RKe of the R gene Xa3/Xa26 family only exists in some rice varieties [9]
All the T0 plants were inoculated with Xoo strain PXO61 at the booting stage and all the plants were susceptible as the wild-type Mudanjiang 8
Summary
Rice Xa3/Xa26 disease-resistance gene encodes a leucine-rich repeat (LRR) receptor kinase-type protein against Xanthomonas oryzae pv. oryzae (Xoo) and belongs to a multigene family. Rice Xa3/Xa26 disease-resistance gene encodes a leucine-rich repeat (LRR) receptor kinase-type protein against Xanthomonas oryzae pv. LRR domain and a transmembrane motif [4]; no rice R gene of this class has been characterized so far. The last class includes the LRR receptor kinase-like R proteins, which are only identified in rice so far [5,6]. Both LRR and kinase domain are common structures in many signaling pathways. All the LRR receptor kinase-like proteins contain a transmembrane motif, which departs the LRR domain to stay outside of the plasma [7]. As cell surface receptors, the LRR receptor kinase-like proteins are thought to recognize special extracellular ligands via the LRR domain and initiate the downstream signaling through the intracellular kinase domain
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