Sulfated RaxX, which represents an unclassified group of ribosomally synthesized post-translationally modified peptides, binds a host immune receptor

Abstract

24The rice immune receptor XA21 is activated by the sulfated microbial peptide 25 RaxX (required for activation of XA21-mediated immunity X) produced by Xanthomonas 26 oryzae pv. oryzae (Xoo). Mutational studies and targeted proteomics revealed that 27RaxX is processed and secreted by the protease/transporter RaxB, whose function can 28 be partially fulfilled by a noncognate peptidase-containing transporter B (PctB). RaxX is 29 cleaved at a Gly-Gly motif, yielding a mature peptide that retains the necessary 30 elements for RaxX function as an immunogen and host peptide hormone mimic. These 31 results indicate that RaxX is a founding member of a previously unclassified and 32 understudied group of tyrosine sulfated RiPPs (ribosomally synthesized, post-33 translationally modified peptides). We further demonstrate that sulfated RaxX directly 34 binds XA21 with high affinity. This work reveals a complete, previously uncharacterized 35 biological process: bacterial RiPP biosynthesis, secretion, binding to a eukaryotic 36 receptor and triggering of a robust host immune response. 37 38 INTRODUCTION 39 40 Ribosomally synthesized and post-translationally modified peptides (RiPPs) 41include anti-microbial, anti-cancer, insecticidal, and quorum sensing peptides (Arnison 42 et al., 2013). RiPPs are structurally and functionally diverse yet share commonalities. 43They are ribosomally synthesized as a precursor peptide with a cleavable N-terminal 44 leader and a post-translationally modified core that becomes the final secreted bioactive 45 RiPP ( Figure 1A; Arnison et al., 2013). Many RiPP leaders direct the modification and/or 46 3 export proteins to the core. This permits the biosynthetic proteins to act on a diverse 47 range of core peptides while maintaining substrate specificity (Oman and van der Donk, 48 2010) and allows for leader peptide-guided designed synthesis of hybrid RiPPs 49 (Burkhart et al., 2017). 50RiPPs achieve substantial chemical diversity through extensive post-translational 51 modifications and are divided into over 20 groups (Arnison et al., 2013). One group that 52 has not been well-studied nor formally categorized as RiPPs are tyrosine sulfated 53 peptides. 54Tyrosine sulfation is a post-translational modification that influences receptor-55 ligand binding in diverse host-microbe interactions (Stone et al., 2009). For example, in 56 humans, tyrosine sulfation of the integral membrane protein CCR5 (C-C chemokine 57 receptor type 5) significantly enhances binding of the human immunodeficiency virus 58 (HIV) envelope glycoprotein, facilitating HIV entry (Farzan et al., 1999). 59In rice, the transmembrane immune receptor XA21, which shares similarities to 60 animal TOLL like receptors (TLRs) and the Arabidopsis flagellin-sensitive 2 (FLS2) and 61 EF-Tu receptors (EFR) (Dardick et al., 2012), responds to sulfated derivatives of the 62 microbial peptide RaxX (required for activation of XA21-mediated immunity X) produced 63 by the Gram-negative pathogenic bacterium Xanthomonas oryzae pv. oryzae (Xoo) 64 ...

The right microbe-associated molecular patterns for effective recognition by plants

“…Another example of MAMP with sequence variant is RaxX, a highly conserved protein in many pathogenic Xanthomonas species. RaxX is recognized by the rice receptor kinase XA21 to confer resistance to most strains of Xoo (Table 1; Wang et al, 1996;Pruitt et al, 2015;Luu et al, 2019). However, Xoo isolates with substitutions of the Y41 residue in RaxX can avoid XA21mediated defense (Pruitt et al, 2015).…”

The Role of Peptide Signals Hidden in the Structure of Functional Proteins in Plant Immune Responses

“…The transmembrane immune receptor-like kinase XA21, which shares homology to Toll-like receptors and flg22 and elf18 receptors, was the first PRR predicted in rice in 1995 [40]. It was only later found that the sulfated peptide from Xanthomonas oryzae protein appears to be a ligand to this receptor [61]. A 16 amino acid peptide, RaxX, is derived from its precursor protein.…”

Variation and inheritance of the XanthomonasraxX‐raxSTAB gene cluster required for activation of XA21‐mediated immunity

“…, ) further processes the sulfated RaxX precursor by removing its double‐glycine leader peptide prior to secretion (Holland et al. , ; Luu et al , ). Core (‘housekeeping’) genes encode the predicted outer membrane TolC channel for the RaxAB complex (da Silva et al.…”