Abstract
The rice XA21 and XA3 pattern receptor kinases, derived from Oryza longistaminata and an Oryza. sativa japonica cultivar Wase Aikoku 3, respectively, confer resistance to strains of the Gram-negative bacterium Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight disease. Previously, we showed that transfer of Xa21 to the model rice cultivar Kitaake enhances resistance to Xoo. In this manuscript we demonstrate that Kitaake expressing Xa3 confers resistance to Xoo strain PXO79 and that the stress-related marker genes PR10b and KO5 are upregulated in Xoo-infected Xa3 rice leaves. We also show that rice somatic embryogenesis receptor kinase 2 (OsSERK2) positively regulates XA3-mediated immunity in Kitaake. We found that overexpression of XA21 binding protein 15 (XB15) and XB24, two negative regulators of XA21-mediated immunity, do not affect XA3-mediated immunity in the Kitaake genetic background. Our results indicate that the rice immune receptors XA21 and XA3 employ both shared and distinct signaling components in their response to Xoo. The results are important to further understand pathogen-associated molecular pattern (PAMP)-triggered immunity in rice. Furthermore, the presence of Kitaake rice carrying Xa3 will facilitate genetic research to study the XA3-mediated immunity.
Highlights
Plants detect and defend against diverse microbes via the innate immune system (Chisholm et al, 2006)
Xa26 was identified in Indica rice cultivar Minghui 63 and later genetic analysis showed that Xa3 and Xa26 are the same gene (Yang et al, 2003; Xiang et al, 2006)
Previous studies showed that Xa3 and Xa21 confer resistance to Xanthomonas oryzae pv. oryzae (Xoo) when introgressed or expressed in diverse rice cultivars (Song et al, 1995; Sun et al, 2004)
Summary
Plants detect and defend against diverse microbes via the innate immune system (Chisholm et al, 2006). One branch of plant innate immunity is mediated by receptors localized on the cell membrane that activate the immune responses upon recognition of extracellular signals derived from pathogens (Boller and Felix, 2009). The Xanthomonas resistance 21 (XA21) and XA3 ( named XA26) receptor kinases confer robust resistance to strains of the Gram-negative bacterium Xanthomonas oryzae pv. XA21 and XA3 belong to the XII subfamily of leucine-rich repeat receptor-like kinases (LRR-RLKs) and share common features. Xa3 Confers Resistance to Xoo in Kitaake typical of LRR-RLK proteins: an extracellular leucine-rich repeat domain, a transmembrane domain, and a cytoplasmic nonarginine-aspartate (non-RD) kinase domain. Like XA21, XA3 confers broadspectrum resistance to most Xoo strains including PXO79 but not PXO99 (Song et al, 1995; Sun et al, 2004)
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