RETRACTED: The Arabidopsis Malectin-Like Leucine-Rich Repeat Receptor-Like Kinase IOS1 Associates with the Pattern Recognition Receptors FLS2 and EFR and Is Critical for Priming of Pattern-Triggered Immunity  

Abstract

Plasma membrane-localized pattern recognition receptors such as FLAGELLIN SENSING2 (FLS2) and EF-TU RECEPTOR (EFR) recognize microbe-associated molecular patterns (MAMPs) to activate the first layer of plant immunity termed patterntriggered immunity (PTI). A reverse genetics approach with genes responsive to the priming agent b-aminobutyric acid (BABA) revealed IMPAIRED OOMYCETE SUSCEPTIBILITY1 (IOS1) as a critical PTI player. Arabidopsis thaliana ios1 mutants were hypersusceptible to Pseudomonas syringae bacteria. Accordingly, ios1 mutants demonstrated defective PTI responses, notably delayed upregulation of PTI marker genes, lower callose deposition, and mitogen-activated protein kinase activities upon bacterial infection or MAMP treatment. Moreover, Arabidopsis lines overexpressing IOS1 were more resistant to P. syringae and demonstrated a primed PTI response. In vitro pull-down, bimolecular fluorescence complementation, coimmunoprecipitation, and mass spectrometry analyses supported the existence of complexes between the membranelocalized IOS1 and FLS2 and EFR. IOS1 also associated with BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1 (BAK1) in a ligand-independent manner and positively regulated FLS2/BAK1 complex formation upon MAMP treatment. Finally, ios1 mutants were defective in BABA-induced resistance and priming. This work reveals IOS1 as a regulatory protein of FLS2-and EFR-mediated signaling that primes PTI activation upon bacterial elicitation.

The Receptor Kinase IMPAIRED OOMYCETE SUSCEPTIBILITY1 Attenuates Abscisic Acid Responses in Arabidopsis

“…During the interaction with filamentous (hemi)biotrophs, however, IOS1 seems to be engaged in a PTI-independent signaling pathway, as we found that the induction of genes involved in early defense signaling (FRK1, NHL10, and WRKY29) upon Hpa infection and callose deposition in the interaction with powdery mildew did not change in ios1-1 when compared with the wild-type plants. Chen et al (2014) also found that IOS1 did not interfere with infection by the necrotrophic fungal pathogen Botrytis cinerea, further supporting a pathogen-dependent role of IOS1. It has to be noted that three allelic mutants, ios1-1, ios1-2, and ios1-3, are available.…”

“…S9). In the interaction with P. syringae, ios1-1, ios1-2, and ios1-3 showed similar PTI defects, and it was also shown that IOS1 requires an active kinase for the association with FLS2 and BAK1 and for the concomitant activation of the PTI response after challenge with P. syringae (Chen et al, 2014). By contrast, signaling is probably independent of the IOS1 kinase activity upon infection with Hpa, because in our hands only ios1-1, but not ios1-2 or ios1-3, was hypersensitive to ABA and more resistant to Hpa (data not shown).…”

“…Our findings determine IOS1 as a plant factor promoting infection by filamentous (hemi)biotrophs and as a negative regulatory element of ABA signaling. By contrast, IOS1 plays a critical role in the onset of PTI during the interaction of Arabidopsis with P. syringae (Chen et al, 2014). It associates with the recognition receptors for bacterial pathogenassociated molecular patterns, FLS2 and EFR, and their coreceptor BAK1.…”

“…It has to be noted that three allelic mutants, ios1-1, ios1-2, and ios1-3, are available. The mutant ios1-1 is a full knockout, whereas both ios1-2 and ios1-3 produce transcripts that probably translate for IOS1 proteins with a truncated kinase domain (Chen et al, 2014;Supplemental Fig. S9).…”

“…This motif is required for establishing the epidermal symbiotic program in roots but not the subsequent cortical symbiosis, suggesting the perception of distinct signals by the extracellular domain of SYMRK during the compatible plant-microbe interaction (Kosuta et al, 2011). IOS1 was recently shown to form a complex with the pattern recognition receptors FLAGELLIN SENSING2 (FLS2) and EF-TU RECEPTOR (EFR), as well as with BAK1, and to prime pattern-triggered immunity (PTI) to the bacterium Pseudomonas syringae (Chen et al, 2014). However, during the interaction of Arabidopsis with Hpa, IOS1 supports the success of downy mildew infection rather than PTI (Hok et al, 2011).…”