The Arabidopsis oligopeptidases TOP1 and TOP2 are salicylic acid targets that modulate SA‐mediated signaling and the immune response

Abstract

These authors contributed equally to this work. SUMMARYSalicylic acid (SA) is a small phenolic molecule with hormonal properties, and is an essential component of the immune response. SA exerts its functions by interacting with protein targets; however, the specific cellular components modulated by SA and critical for immune signal transduction are largely unknown. To uncover cellular activities targeted by SA, we probed Arabidopsis protein microarrays with a functional analog of SA. We demonstrate that thimet oligopeptidases (TOPs) constitute a class of SA-binding enzymes. Biochemical evidence demonstrated that SA interacts with TOPs and inhibits their peptidase activities to various degrees both in vitro and in plant extracts. Functional characterization of mutants with altered TOP expression indicated that TOP1 and TOP2 mediate SA-dependent signaling and are necessary for the immune response to avirulent pathogens. Our results support a model whereby TOP1 and TOP2 act in separate pathways to modulate SA-mediated cellular processes.

The Raf-like kinase ILK1 and the high affinity K+ transporter HAK5 are required for Innate Immunity and Abiotic Stress Response

“…RNA isolation and cDNA synthesis for expression analysis of 2-week-old seedlings with and without stress treatments were performed as described previously in Moreau et al (2013). Biological replicates contained 15-20 seedlings and qRT PCR was performed in 20 mL reactions using iTAQ SYBR Green (BioRad, Hercules, CA).…”

Hormone Signaling: Current Perspectives on the Roles of Salicylic Acid and Its Derivatives in Plants

“…Further Arabidopsis SA-binding proteins are the thimet oligopeptidases (TOP1 and TOP2) [ 81 ], identifi ed using protein microarrays. SA inhibits the enzymatic activity of TOP1 and TOP2, and both are known to play a role in plant immunity against avirulent pathogens [ 81 ]. A recent X-ray diffraction analysis using Arabidopsis TOP2 did not support its binding to SA [ 110 ].…”

Structure of theArabidopsis thalianaTOP2 oligopeptidase

“…The plant Arabidopsis thaliana encodes three TOP enzymes, TOP1 (At5g65620) (Moreau et al , 2013), also known as TOPorg (Polge et al , 2009) and organellar oligopeptidase (OOP) (Kmiec et al , 2013), TOP2 (At5g10540), and TOP-like (TOPL, At1g67690) (Polge et al , 2009). TOP2 and TOPL are cytoplasmic enzymes (Ito et al , 2011), while TOP1 is located in the chloroplast (Ferro et al , 2010, Olinares et al , 2010, Moreau et al , 2013).…”

“…TOP2 and TOPL are cytoplasmic enzymes (Ito et al , 2011), while TOP1 is located in the chloroplast (Ferro et al , 2010, Olinares et al , 2010, Moreau et al , 2013). TOP2 shares 93% amino acid sequence identity with TOP1 and 27% identity with the human TOP (Fig.…”

“…Recent studies suggest that TOP1 and TOP2 may be targets for salicylic acid (SA) (Moreau et al , 2013). TOP1 was identified by screening an Arabidopsis protein microarray for proteins that could be cross-linked to the photo-activated SA analog 4-azido-SA.…”