Rice XA21 Binding Protein 3 Is a Ubiquitin Ligase Required for Full Xa21-Mediated Disease Resistance

Abstract

XA21 is a receptor-like kinase protein in rice (Oryza sativa) that confers gene-for-gene resistance to specific races of the causal agent of bacterial blight disease, Xanthomonas oryzae pv oryzae. We identified XA21 binding protein 3 (XB3), an E3 ubiquitin ligase, as a substrate for the XA21 Ser and Thr kinase. The interaction between XB3 and the kinase domain of XA21 has been shown in yeast and in vitro, and the physical association between XB3 and XA21 in vivo has also been confirmed by coimmunoprecipitation assays. XB3 contains an ankyrin repeat domain and a RING finger motif that is sufficient for its interaction with the kinase domain of XA21 and for its E3 ubiquitin ligase activity, respectively. Transgenic plants with reduced expression of the Xb3 gene are compromised in resistance to the avirulent race of X. oryzae pv oryzae. Furthermore, reduced levels of Xb3 lead to decreased levels of the XA21 protein. These results indicate that Xb3 is necessary for full accumulation of the XA21 protein and for Xa21-mediated resistance.

Rice RING protein OsBBI1 with E3 ligase activity confers broad-spectrum resistance against Magnaporthe oryzae by modifying the cell wall defence

“…Loss of OsBBI1 function resulted in increased susceptibility, whereas overexpression of OsBBI1 in transgenic plants led to enhanced resistance against multiple races of M. oryzae Figures 2 and 3), indicating that OsBBI1 confers broadspectrum resistance in rice against blast disease. Several E3 ligases in rice have been reported to be involved in innate immunity [29][30][31]. However, OsBBI1 is distinct from the E3 ligases previously reported to be involved in rice innate immunity in terms of structural characteristics and biological functions.…”

“…In rice, several proteins with activity of E3 Ubi ligases, a group of enzymes required for ubiquitination of substrate proteins in the Ubi/26S proteasome system, are involved in regulating innate immune response [29][30][31]. For example, SPL1, a U-box protein with E3 Ubi ligase activity, is a negative regulator of cell death and innate immunity against M. oryzae and Xanthomonas oryzae pv.…”

“…oryzae (Xoo), the causal agent of bacterial leaf blight disease [30]. XB3, an E3 Ubi ligase, is necessary for full accumulation of the XA21 protein and for XA21-mediated innate immune response against Xoo [31]. XA21 was recently identified as a PRR with race-specific feature against Xoo [32].…”

Arabidopsis ubiquitin ligase MIEL1 mediates degradation of the transcription factor MYB30 weakening plant defence

“…In addition, the Arabidopsis F-box protein CPR1 targets several resistance proteins for degradation, thereby regulating their accumulation and preventing autoimmunity 18,19 . The rice XA21-binding protein3 (XB3) is an active RING-type E3 ligase that binds to the kinase domain of the resistance protein XA21 and is substrate for the XA21 kinase activity 20 . Although XB3 is necessary for full accumulation of XA21 and for XA21-mediated resistance in rice, its targets remain to be discovered 20 .…”

“…The rice XA21-binding protein3 (XB3) is an active RING-type E3 ligase that binds to the kinase domain of the resistance protein XA21 and is substrate for the XA21 kinase activity 20 . Although XB3 is necessary for full accumulation of XA21 and for XA21-mediated resistance in rice, its targets remain to be discovered 20 . The important role of ubiquitination-related processes during the regulation of plant responses to pathogens is underlined by the finding that most microbes appear to have evolved a way to subvert the host UPS to promote disease 14,15 .…”