In order to resist pathogens plants have evolved so‐called pattern recognition receptors (PRR) for early
detection of microbe‐associated molecular patterns (MAMPs). Binding of these molecules to their
cognate PRR leads to the activation of plant immunity (MTI).
Recently, it has been shown that accumulation and function of the PRR EFR that recognizes the bacterial
elongation factor (EF)‐Tu epitope elf18, is dependent on functional endoplasmic reticulum (ER)‐resident
glucosidase II (GII). A weakly dysfunctional gIIa allele, designated rsw3, is impaired in late and sustained
activation of defense‐related genes, despite wild‐type like early defense activation upon elf18 treatment.
Nevertheless, rsw3 plants exhibit a super‐susceptible phenotype towards Pseudomonas syringae pv.
tomato and fail to induce EFR‐mediated resistance. Those findings indicate the significance of sustained
MTI activation for robust defence execution. However, the mechanism linking initial MAMP detection to
robust and sustained immune activation remains elusive.
A whole genome transcript analysis revealed a group of genes which failed to be induced in rsw3 at 10
hours post treatment with elf18. In silico analysis provided evidence for those genes to be directly
involved in defense execution in the presence of pathogens. Among those genes we identified PBS3.
Analysis of pbs3 plants exhibited a similar phenotype as rsw3 plants showing impairment in sustained
elf18‐triggered transcriptional reprogramming, pointing to an important role of the PBS3 enzyme and its
catalysed products during EFR‐mediated immunity.
In addition, EFR‐induced sustained PROPEP2 and PROPEP3 up‐regulation could not be maintained in
rsw3 plants. Those genes encode for two putative precursor proteins of endogenous elicitor peptides in
Arabidopsis. The Leu‐rich repeat receptor kinases PEPR1 and PEPR2 recognize the Pep‐epitopes,
triggering immune outputs which are reminiscent of MAMP responses. Those findings suggest that the
Pep/PEPR pathway acts as an amplifying machinery of MTI. In this respect, sustained induction of
PROPEP2 and PROPEP3 upon elf18‐elicitation might represent a mechanism of linking initial MAMP
signaling activation to robust immunity.
Here we show that basal defense against hemibiotrophic pathogens as well as the generation of SAR is
compromised in pepr1 pepr2 plants, providing evidence for a role of this signaling system in plant
immunity. By analyzing genome‐wide transcriptional changes, we obtained commonalities and
differences between EFR‐ and PEPR‐regulated genes and pathways. Our data indicate that Pep/PEPR
signaling activation facilitates co‐activation of typically antagonizing salicylate and jasmonate pathways,
consistent with a role of PEPRs for defenses against hemibiotrophic pathogens. Interestingly, the
expression of PROPEP2 and PROPEP3 is predominantly detectable at local challenged sites during SAR,
pointing to a role of the Pep/PEPR pathway in the generation of systemic immune signals.
In sum, the data presented in this work uncover possible novel mechanism linking MTI activation to
defense execution and reveal new insights into the function of the PEPR signaling pathway during basal
defense and SAR
