Uncovering the Mechanisms: The Role of Biotrophic Fungi in Activating or Suppressing Plant Defense Responses.

This paper discusses the mechanisms by which fungi manipulate plant physiology and suppress plant defense responses by producing effectors that can target various host proteins. Effector-triggered immunity and effector-triggered susceptibility are pivotal elements in the complex molecular dialogue underlying plant-pathogen interactions. Pathogen-produced effector molecules possess the ability to mimic pathogen-associated molecular patterns or hinder the binding of pattern recognition receptors. Effectors can directly target nucleotide-binding domain, leucine-rich repeat receptors, or manipulate downstream signaling components to suppress plant defense. Interactions between these effectors and receptor-like kinases in host plants are critical in this process. Biotrophic fungi adeptly exploit the signaling networks of key plant hormones, including salicylic acid, jasmonic acid, abscisic acid, and ethylene, to establish a compatible interaction with their plant hosts. Overall, the paper highlights the importance of understanding the complex interplay between plant defense mechanisms and fungal effectors to develop effective strategies for plant disease management.

Proteomic and Transcriptomic Analyses Indicate Metabolic Changes and Reduced Defense Responses in Mycorrhizal Roots of Oeceoclades maculata (Orchidaceae) Collected in Nature.

Orchids form endomycorrhizal associations with fungi mainly belonging to basidiomycetes. The molecular events taking place in orchid mycorrhiza are poorly understood, although the cellular changes necessary to accommodate the fungus and to control nutrient exchanges imply a modulation of gene expression. Here, we used proteomics and transcriptomics to identify changes in the steady-state levels of proteins and transcripts in the roots of the green terrestrial orchid Oeceoclades maculata. When mycorrhizal and non-mycorrhizal roots from the same individuals were compared, 94 proteins showed differential accumulation using the label-free protein quantitation approach, 86 using isobaric tagging and 60 using 2D-differential electrophoresis. After de novo assembly of transcriptomic data, 11,179 plant transcripts were found to be differentially expressed, and 2175 were successfully annotated. The annotated plant transcripts allowed the identification of up- and down-regulated metabolic pathways. Overall, proteomics and transcriptomics revealed, in mycorrhizal roots, increased levels of transcription factors and nutrient transporters, as well as ethylene-related proteins. The expression pattern of proteins and transcripts involved in plant defense responses suggested that plant defense was reduced in O. maculata mycorrhizal roots sampled in nature. These results expand our current knowledge towards a better understanding of the orchid mycorrhizal symbiosis in adult plants under natural conditions.

DOTAP, a lipidic transfection reagent, triggers Arabidopsis plant defense responses.

MAIN CONCLUSION: DOTAP triggers Arabidopsis thaliana immunity and by priming the defense response is able to reduce bacterial pathogen attack. DOTAP is a cationic lipid widely used as a liposomal transfection reagent and it has recently been identified as a strong activator of the innate immune system in animal cells. Plants are sessile organisms and unlike mammals, that have innate and acquired immunity, plants possess only innate immunity. A key feature of plant immunity is the ability to sense potentially dangerous signals, as it is the case for microbe-associated, pathogen-associated or damage-associated molecular patterns and by doing so, trigger an active defense response to cope with the perturbing stimulus. Here, we evaluated the effect of DOTAP in plant basal innate immunity. An initial plant defense response was induced by the cationic lipid DOTAP in the model plant Arabidopsis thaliana, assessed by callose deposition, reactive oxygen species production, and plant cell death. In addition, a proteomic analysis revealed that these responses are mirrored by changes in the plant proteome, such as up-regulation of proteins related to defense responses, including proteins involved in photorespiration, cysteine and oxylipin synthesis, and oxidative stress response; and down-regulation of enzymes related to photosynthesis. Furthermore, DOTAP was able to prime the defense response for later pathogenic challenges as in the case of the virulent bacterial pathogen Pseudomonas syringae pv. tomato. Disease outcome was diminished in DOTAP-pre-treated leaves and bacterial growth was reduced 100 times compared to mock leaves. Therefore, DOTAP may be considered a good candidate as an elicitor for the study of plant immunity.

Compounds Released by the Biocontrol Yeast Hanseniaspora opuntiae Protect Plants Against Corynespora cassiicola and Botrytis cinerea.

Plant diseases induced by fungi are among the most important limiting factors during pre- and post-harvest food production. For decades, synthetic chemical fungicides have been used to control these diseases, however, increase on worldwide regulatory policies and the demand to reduce their application, have led to searching for new ecofriendly alternatives such as the biostimulants. The commercial application of yeasts as biocontrol agents, has shown low efficacy compared to synthetic fungicides, mostly due to the limited knowledge of the molecular mechanisms of yeast-induced responses. To date, only two genome-wide transcriptomic analyses have characterized the mode of action of biocontrols using the plant model Arabidopsis thaliana, missing, in our point of view, all its molecular and genomic potential. Here we describe that compounds released by the biocontrol yeast Hanseniaspora opuntiae (HoFs) can protect Glycine max and Arabidopsis thaliana plants against the broad host-range necrotrophic fungi Corynespora cassiicola and Botrytis cinerea. We show that HoFs have a long-lasting, dose-dependent local, and systemic effect against Botrytis cinerea. Additionally, we performed a genome-wide transcriptomic analysis to identify genes differentially expressed after application of HoFs in Arabidopsis thaliana. Our work provides novel and valuable information that can help researchers to improve HoFs efficacy in order for it to become an ecofriendly alternative to synthetic fungicides.