Beschreibung:
<jats:p>
Detection of microbes by plants relies in part on an array of pattern-recognition receptors that recognize conserved microbial signatures, so-called “microbe-associated molecular patterns.” The
<jats:italic>Arabidopsis thaliana</jats:italic>
receptor-like kinase FLS2 is the pattern-recognition receptor for bacterial flagellin. Similarly to FLS2, the rice transmembrane protein XA21 is the receptor for the sulfated form of the
<jats:italic>Xanthomonas oryzae</jats:italic>
pv.
<jats:italic>oryzae</jats:italic>
secreted protein Ax21. Here we show that Ax21-derived peptides activate
<jats:italic>Arabidopsis</jats:italic>
immunity, triggering responses similar to those elicited by flagellin, including an oxidative burst, induction of defense-response genes, and enhanced resistance to bacterial pathogens. To identify
<jats:italic>Arabidopsis Xa21</jats:italic>
functional homologs, we used a reverse genetics approach to screen T-DNA insertion mutants corresponding to all 47 of the
<jats:italic>Arabidopsis</jats:italic>
genes encoding non-RD kinases belonging to the interleukin-1 receptor-associated kinase (IRAK) family. Surprisingly, among all of these mutant lines, only
<jats:italic>fls2</jats:italic>
mutants exhibited a significant loss of response to Ax21-derived peptides. Ax21 peptides also failed to activate defense-related responses in an
<jats:italic>fls2-24</jats:italic>
mutant that does not bind Flg22. Moreover, a Flg22Δ2 variant of Flg22 that binds to FLS2 but does not activate FLS2-mediated signaling suppressed Ax21-derived peptide signaling, indicating mutually exclusive perception of Flg22 or Ax21 peptides by FLS2. The data indicate that FLS2 functions beyond flagellin perception to detect other microbe-associated molecular patterns.
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