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Open Access Publications from the University of California

Biosynthesis and secretion of the microbial sulfated peptide RaxX and binding to the rice XA21 immune receptor.

  • Author(s): Luu, Dee Dee;
  • Joe, Anna;
  • Chen, Yan;
  • Parys, Katarzyna;
  • Bahar, Ofir;
  • Pruitt, Rory;
  • Chan, Leanne Jade G;
  • Petzold, Christopher J;
  • Long, Kelsey;
  • Adamchak, Clifford;
  • Stewart, Valley;
  • Belkhadir, Youssef;
  • Ronald, Pamela C
  • et al.

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The rice immune receptor XA21 is activated by the sulfated microbial peptide required for activation of XA21-mediated immunity X (RaxX) produced by Xanthomonas oryzae pv. oryzae (Xoo). Mutational studies and targeted proteomics revealed that the RaxX precursor peptide (proRaxX) is processed and secreted by the protease/transporter RaxB, the function of which can be partially fulfilled by a noncognate peptidase-containing transporter component B (PctB). proRaxX is cleaved at a Gly-Gly motif, yielding a mature peptide that retains the necessary elements for RaxX function as an immunogen and host peptide hormone mimic. These results indicate that RaxX is a prokaryotic member of a previously unclassified and understudied group of eukaryotic tyrosine sulfated ribosomally synthesized, posttranslationally modified peptides (RiPPs). We further demonstrate that sulfated RaxX directly binds XA21 with high affinity. This work reveals a complete, previously uncharacterized biological process: bacterial RiPP biosynthesis, secretion, binding to a eukaryotic receptor, and triggering of a robust host immune response.

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