Revealing the secrets beneath grapevine and Plasmopara viticola early communication: a picture of host and pathogen proteomes

Plant apoplast is the first hub of plant-pathogen communication where pathogen effectors are recognized by plant defensive proteins and cell receptors and several signal transduction pathways are activated. As a result of this first contact, the host triggers a defence response that involves the modulation of several extra and intracellular proteins. In grapevine-pathogen interactions, little is known about the communication between cells and apoplast. Also, the role of apoplastic proteins in response to pathogens still remains a blackbox. In this study we focused on the first 6 hours after Plasmopara viticola inoculation to evaluate grapevine proteome modulation in the apoplastic fluid (APF) and whole leaf tissue. Plasmopara viticola proteome was also assessed enabling a deeper understanding of plant and pathogen communication. Our results showed that oomycete recognition, plant cell wall modifications, ROS signalling and disruption of oomycete structures are triggered in Regent after P. viticola inoculation. Our results highlight a strict relation between the apoplastic pathways modulated and the proteins identified in the whole leaf proteome. On the other hand, P. viticola proteins related to growth/morphogenesis and virulence mechanisms were the most predominant. This pioneer study highlights the early dynamics of extra and intracellular communication in grapevine defence activation that leads to the successful establishment of an incompatible interaction.

Arabidopsis Apoplastic Fluid Contains sRNA- and Circular RNA-Protein Complexes that Are Located Outside Extracellular Vesicles

Previously, we have shown that apoplastic wash fluid purified from Arabidopsis leaves contains small RNAs (sRNAs). To investigate whether these sRNAs are encapsulated inside extracellular vesicles (EVs), we treated EVs isolated from Arabidopsis leaves with the protease trypsin and RNase A, which should degrade RNAs located outside EVs but not those located inside. These analyses revealed that apoplastic RNAs are mostly located outside EVs and are associated with proteins. Further analyses of these extracellular RNAs (exRNAs) revealed that they comprise both sRNAs and long non-coding RNAs (lncRNAs), including circular RNAs (circRNAs). We also found that exRNAs are highly enriched in the post-transcriptional modification N6-methyladenine (m(6)A). Consistent with this, we identified a putative m(6)A-binding protein in apoplastic wash fluid, GLYCINE-RICH RNA-BINDING PROTEIN 7 (GRP7), as well as the small RNA-binding protein ARGONAUTE2 (AGO2). These two proteins co-immunoprecipitated with each other, and with lncRNAs, including circRNAs. Mutation of GRP7 or AGO2 caused changes in both the sRNA and lncRNA content of apoplastic wash fluid, suggesting that these proteins contribute to the secretion and/or stabilization of exRNAs. We propose that these extravesicular RNAs mediate host-induced gene silencing, rather than RNA inside EVs.

Proteomic Analysis of Pathogen-Responsive Proteins from Maize Stem Apoplast Triggered by Fusarium Verticillioides

Background:Plant apoplast is the frontline battlefield between the host and the invading pathogen. In response to the pathogen attack, a variety of defense-associated proteins are secreted by the host plant in the apoplast to impede the perceived attack. To better understand the plant response after Fusarium verticillioides attack, proteomic analyses of the maize apoplastic fluid was done using LC-MS/MS coupled with label-free quantification. Results:In total, 742 proteins responsive to the F. verticillioides infection were identified. Among them, 158 were differentially accumulated proteins (DAPs). Out of these 158 proteins, 35 were upregulated, and 18 were down-regulated, whereas, 65 and 40 unique proteins were identified from inoculated and un-inoculated plants, respectively. Enrichment analyses categorized the proteins into 4 pathways, and biosynthesis of amino acid was the prominent pathway followed by the metabolic pathways. Moreover, 86 DAPs were predicted as secretory proteins. The identified secreted proteins were related to a variety of pathways in defense responses, including cell redox homeostasis, cell wall modification, signal transduction, carbohydrate metabolism, and others.Conclusions:Our data suggested that the maize plants carried out a rigorous reprogramming of the proteins in the apoplastic region to cope with the attack of F. verticillioides.

Mangroves in the Leaves: Anatomy, Physiology, and Immunity of Epithemal Hydathodes

Hydathodes are organs found on aerial parts of a wide range of plant species that provide almost direct access for several pathogenic microbes to the plant vascular system. Hydathodes are better known as the site of guttation, which is the release of droplets of plant apoplastic fluid to the outer leaf surface. Because these organs are only described through sporadic allusions in the literature, this review aims to provide a comprehensive view of hydathode development, physiology, and immunity by compiling a historic and contemporary bibliography. In particular, we refine the definition of hydathodes.We illustrate their important roles in the maintenance of plant osmotic balance, nutrient retrieval, and exclusion of deleterious chemicals from the xylem sap. Finally, we present our current understanding of the infection of hydathodes by adapted vascular pathogens and the associated plant immune responses.