Logistics of defense: The contribution of endomembranes to plant innate immunity.

Phytopathogens cause plant diseases that threaten food security. Unlike mammals, plants lack an adaptive immune system and rely on their innate immune system to recognize and respond to pathogens. Plant response to a pathogen attack requires precise coordination of intracellular traffic and signaling.

Defense against phytopathogens relies on efficient antimicrobial protein secretion mediated by the microtubule-binding protein TGNap1.

Plant immunity depends on the secretion of antimicrobial proteins, which occurs through yet-largely unknown mechanisms. The trans-Golgi network (TGN), a hub for intracellular and extracellular trafficking pathways, and the cytoskeleton, which is required for antimicrobial protein secretion, are emerging as pathogen targets to dampen plant immunity. In this work, we demonstrate that tgnap1-2, a loss-of-function mutant of Arabidopsis TGNap1, a TGN-associated and microtubule (MT)-binding protein, is susceptible to Pseudomonas syringae (Pst DC3000).

Immune activation during Pseudomonas infection causes local cell wall remodeling and alters AGP accumulation.

The plant cell boundary generally comprises constituents of the primary and secondary cell wall (CW) that are deposited sequentially during development. Although it is known that the CW acts as a barrier against phytopathogens and undergoes modifications to limit their invasion, the extent, sequence, and requirements of the pathogen-induced modifications of the CW components are still largely unknown, especially at the level of the polysaccharide fraction. To address this significant knowledge gap, we adopted the compatible Pseudomonas syringae-Arabidopsis thaliana system.

Chemoproteomics Reveals the Pan-HER Kinase Inhibitor Neratinib To Target an Epoxide Hydrolase Related to Phytohormone Signaling.

Plant phytohormone pathways are regulated by an intricate network of signaling components and modulators, many of which still remain unknown. Here, we report a forward chemical genetics approach for the identification of functional SA agonists in that revealed Neratinib (), a covalent pan-HER kinase inhibitor drug in humans, as a modulator of SA signaling. Instead of a protein kinase, chemoproteomics unveiled that covalently modifies a surface-exposed cysteine residue of epoxide hydrolase isoform 7 (AtEH7), thereby triggering its allosteric inhibition.

Cavity surface residues of PAD4 and SAG101 contribute to EDS1 dimer signaling specificity in plant immunity.

Arabidopsis pathogen effector-triggered immunity (ETI) is controlled by a family of three lipase-like proteins (EDS1, PAD4, and SAG101) and two subfamilies of HET-S/LOB-B (HeLo)-domain "helper" nucleotide-binding/leucine-rich repeats (ADR1s and NRG1s). EDS1-PAD4 dimers cooperate with ADR1s, and EDS1-SAG101 dimers with NRG1s, in two separate defense-promoting modules. EDS1-PAD4-ADR1 and EDS1-SAG101-NRG1 complexes were detected in immune-activated leaf extracts but the molecular determinants for specific complex formation and function remain unknown.

Bacterial effector targeting of a plant iron sensor facilitates iron acquisition and pathogen colonization.

Acquisition of nutrients from different species is necessary for pathogen colonization. Iron is an essential mineral nutrient for nearly all organisms, but little is known about how pathogens manipulate plant hosts to acquire iron. Here, we report that AvrRps4, an effector protein delivered by Pseudomonas syringae bacteria to plants, interacts with and targets the plant iron sensor protein BRUTUS (BTS) to facilitate iron uptake and pathogen proliferation in Arabidopsis thaliana.

Plant endomembranes and cytoskeleton: moving targets in immunity.

Pathogens attack plant cells to divert resources toward pathogen proliferation. To resist pathogens, plant cells rely on multilayered signaling pathways that hinge upon the secretory pathway for the synthesis and trafficking of pathogen sensors and defense molecules. In recent years, significant strides have been made in the understanding of the functional relationship between pathogen response and membrane traffic.

Origins and Immunity Networking Functions of EDS1 Family Proteins.

The EDS1 family of structurally unique lipase-like proteins EDS1, SAG101, and PAD4 evolved in seed plants, on top of existing phytohormone and nucleotide-binding-leucine-rich-repeat (NLR) networks, to regulate immunity pathways against host-adapted biotrophic pathogens. Exclusive heterodimers between EDS1 and SAG101 or PAD4 create essential surfaces for resistance signaling. Phylogenomic information, together with functional studies in and tobacco, identify a coevolved module between the EDS1-SAG101 heterodimer and coiled-coil (CC) HET-S and LOP-B (CC) domain helper NLRs that is recruited by intracellular Toll-interleukin1-receptor (TIR) domain NLR receptors to confer host cell death and pathogen immunity.

EDR1 Protein Kinase Regulates the Association of EDS1 and PAD4 to Inhibit Cell Death.

ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and PHYTOALEXIN DEFICIENT4 (PAD4) are sequence-related lipase-like proteins that function as a complex to regulate defense responses in by both salicylic acid-dependent and independent pathways. Here, we describe a gain-of-function mutation in PAD4 (S135F) that enhances resistance and cell death in response to infection by the powdery mildew pathogen The mutant PAD4 protein accumulates to wild-type levels in cells, thus these phenotypes are unlikely to be due to PAD4 over accumulation. The phenotypes are similar to loss-of-function mutations in the protein kinase EDR1 (Enhanced Disease Resistance1), and previous work has shown that loss of or suppresses mediated phenotypes, placing these proteins downstream of .

The PAD4 Lipase-Like Domain Is Sufficient for Resistance to Green Peach Aphid.

Plants have evolved mechanisms to protect themselves against pathogenic microbes and insect pests. In , the immune regulator PAD4 functions with its cognate partner EDS1 to limit pathogen growth. PAD4, independently of EDS1, reduces infestation by green peach aphid (GPA).

Arabidopsis immunity regulator EDS1 in a PAD4/SAG101-unbound form is a monomer with an inherently inactive conformation.

In plant innate immunity, enhanced disease susceptibility 1 (EDS1) integrates all pathogen-induced signals transmitted by TIR-type NLR receptors. Driven by an N-terminal α/β-hydrolase-fold domain with a protruding interaction helix, EDS1 assembles with two homologs, phytoalexin-deficient 4 (PAD4) and senescence-associated gene 101 (SAG101). The resulting heterodimers are critical for EDS1 function and structurally well characterized.

An EDS1 heterodimer signalling surface enforces timely reprogramming of immunity genes in Arabidopsis.

Plant intracellular NLR receptors recognise pathogen interference to trigger immunity but how NLRs signal is not known. Enhanced disease susceptibility1 (EDS1) heterodimers are recruited by Toll-interleukin1-receptor domain NLRs (TNLs) to transcriptionally mobilise resistance pathways. By interrogating the Arabidopsis EDS1 ɑ-helical EP-domain we identify positively charged residues lining a cavity that are essential for TNL immunity signalling, beyond heterodimer formation.

Antagonism of Transcription Factor MYC2 by EDS1/PAD4 Complexes Bolsters Salicylic Acid Defense in Arabidopsis Effector-Triggered Immunity.

In plant immunity, pathogen-activated intracellular nucleotide binding/leucine rich repeat (NLR) receptors mobilize disease resistance pathways, but the downstream signaling mechanisms remain obscure. Enhanced disease susceptibility 1 (EDS1) controls transcriptional reprogramming in resistance triggered by Toll-Interleukin1-Receptor domain (TIR)-family NLRs (TNLs). Transcriptional induction of the salicylic acid (SA) hormone defense sector provides one crucial barrier against biotrophic pathogens.