Plant immunity: Rice XA21-mediated resistance to bacterial infection

Abstract

In this article, we describe the development of the plant immunity field, starting with efforts to understand the genetic basis for disease resistance, which ∼30 y ago led to the discovery of diverse classes of immune receptors that recognize and respond to infectious microbes. We focus on knowledge gained from studies of the rice XA21 immune receptor that recognizes RaxX (required for activation of XA21 mediated immunity X), a sulfated microbial peptide secreted by the gram-negative bacterium Xanthomonas oryzae pv. oryzae. XA21 is representative of a large class of plant and animal immune receptors that recognize and respond to conserved microbial molecules. We highlight the complexity of this large class of receptors in plants, discuss a possible role for RaxX in Xanthomonas biology, and draw attention to the important role of sulfotyrosine in mediating receptor–ligand interactions.

Transcriptional regulator Sar regulates the multiple secretion systems in Xanthomonas oryzae

“…The rice receptor‐like kinase Xa21 provides immunity against Xoo strains that carry raxX ( AvrXa21 ). The T1SS‐related rax genes of Xoo are also required for RaxX activity (Ercoli et al, 2022 ). Sar could be involved in activating the transcription of the raxSTAB gene cluster according to our previous RNA‐Seq data and the bacterial one‐hybrid assay (Zheng et al, 2021 ) (Figure 2a ).…”

“…The first gene in the raxSTAB operon, raxST, encodes a sulfotransferase-like protein (Han et al, 2012). A sulfated RaxX (AvrXa21) secreted by the T1SS is required to activate Xa21-mediated recognition and immunity (Ercoli et al, 2022;Han et al, 2012;Luu et al, 2019;da Silva et al, 2004).…”

“…The first gene in the raxSTAB operon, raxST , encodes a sulfotransferase‐like protein (Han et al, 2012 ). A sulfated RaxX (AvrXa21) secreted by the T1SS is required to activate Xa21‐mediated recognition and immunity (Ercoli et al, 2022 ; Han et al, 2012 ; Luu et al, 2019 ; da Silva et al, 2004 ). It has been reported that the RaxR‐RaxH two‐component system (TCS) regulates the expression of eight rax genes (Lee et al, 2006 , 2008 ).…”

Climate change challenges, plant science solutions

“…Another strategy well-aligned with sustainable agriculture practices is the introduction of genetic improvements that protect crops against pathogens and confer resilience to abiotic stress in a heritable manner. There are numerous examples of genetic alterations in crops leading to resistance to specific pathogens, many of which were achieved through the introduction of immune receptors ( Ercoli et al, 2022 ). Immune receptors are activated by direct or indirect interaction with microbial molecules to elicit host defense responses.…”

The warfare for plant highway: vascular plant–microbe interaction pinpoints lignin

“…For example, rice Xa21, a leucine-rich repeat (LRR) receptor-like kinase (RLK), may recognize RaxX (required for activation of XA21mediated immunity X), a ligand from Xanthomonas oryzae pv. oryzae (Xoo), to mediate resistance against Xoo (Ercoli et al, 2022). Tomato Ve1 is a LRR receptorlike protein (RLP) that confers resistance against race1 isolates of Verticillium dahliae and V.albo-atrum by perceiving Ave1 effectors, whose homologs are widely distributed in several vascular wilt fungus pathogens (de Jonge et al, 2012).…”