Unique characteristics of Xanthomonas oryzae pv. oryzae AvrXa21 and implications for plant innate immunity

Sang Won Lee, Sang Wook Han, Laura E. Bartley, Pamela C. Ronald

Research output: Contribution to journalReview articlepeer-review

91 Citations (Scopus)

Abstract

This article provides a brief overview of some of the major concepts and molecular features of plant and animal innate immune systems. The rice pathogen recognition receptor, XA21, confers resistance to Xanthomonas oryzae pv. oryzae strains producing the AvrXa21 elicitor. Xa21 codes for a receptor-like kinase consisting of an extracellular leucine-rich repeat domain, a transmembrane domain, and a cytoplasmic kinase domain. We show that AvrXa21 activity requires the presence of rax (required for AvrXa21) A, raxB, and raxC genes that encode components of a type one secretion system. In contrast, an hrpC- strain deficient in type three secretion maintains AvrXa21 activity. Xanthomonas campestris pv. campestris can express AvrXa21 activity if raxST, encoding a putative sulfotransferase, and raxA are provided in trans. Expression of rax genes depends on population density and other functioning rax genes. This and other data suggest that the AvrXa21 pathogen-associated molecule is involved in quorum sensing. Together these data suggest that AvrXa21 represents a previously uncharacterized class of Gram-negative bacterial signaling molecules. These results from our studies of the XA21/AvrXa21 interaction call for some modifications in the way we think about innate immunity strategies.

Original languageEnglish
Pages (from-to)18395-18400
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume103
Issue number49
DOIs
Publication statusPublished - 5 Dec 2006

Keywords

  • Pathogen-associated molecule pattern
  • Quorum sensing
  • Rice
  • Type I secretion
  • XA21

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