Unraveling the protein network of tomato fruit in response to necrotrophic phytopathogenic Rhizopus nigricans

Regulation of heat shock proteins 70 and their role in plant immunity

Heat shock proteins 70 (HSP70s) are steadily gaining more attention in the field of plant biotic interactions. Though their regulation and activity in plants are much less well characterized than are those of their counterparts in mammals, accumulating evidence indicates that the role of HSP70-mediated defense mechanisms in plant cells is indispensable. In this review, we summarize current knowledge of HSP70 post-translational control in plants. We comment on the phytohormonal regulation of HSP70 expression and protein abundance, and identify a prominent role for cytokinin in HSP70 control. We outline HSP70s' subcellular localizations, chaperone activity, and chaperone-mediated protein degradation. We focus on the role of HSP70s in plant pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity, and discuss the contribution of different HSP70 subfamilies to plant defense against pathogens.

Heat Shock Proteins: Dynamic Biomolecules to Counter Plant Biotic and Abiotic Stresses

Due to the present scenario of climate change, plants have to evolve strategies to survive and perform under a plethora of biotic and abiotic stresses, which restrict plant productivity. Maintenance of plant protein functional conformation and preventing non-native proteins from aggregation, which leads to metabolic disruption, are of prime importance. Plant heat shock proteins (HSPs), as chaperones, play a pivotal role in conferring biotic and abiotic stress tolerance. Moreover, HSP also enhances membrane stability and detoxifies the reactive oxygen species (ROS) by positively regulating the antioxidant enzymes system. Additionally, it uses ROS as a signal to molecules to induce HSP production. HSP also enhances plant immunity by the accumulation and stability of pathogenesis-related (PR) proteins under various biotic stresses. Thus, to unravel the entire plant defense system, the role of HSPs are discussed with a special focus on plant response to biotic and abiotic stresses, which will be helpful in the development of stress tolerance in plant crops.

Genome-Wide Analysis of Watermelon HSP20s and Their Expression Profiles and Subcellular Locations under Stresses

Watermelon (Citrullus lanatus L.), which is an economically important cucurbit crop that is cultivated worldwide, is vulnerable to various adverse environmental conditions. Small heat shock protein 20s (HSP20s) are the most abundant plant HSPs and they play important roles in various biotic and abiotic stress responses. However, they have not been systematically investigated in watermelon. In this study, we identified 44 watermelon HSP20 genes and analyzed their gene structures, conserved domains, phylogenetic relationships, chromosomal distributions, and expression profiles. All of the watermelon HSP20 proteins have a conserved the α-crystallin (ACD) domain. Half of the ClHSP20s arose through gene duplication events. Plant HSP20s were grouped into 18 subfamiles and a new subfamily, nucleo-cytoplasmic XIII (CXIII), was identified in this study. Numerous stress- and hormone-responsive cis-elements were detected in the putative promoter regions of the watermelon HSP20 genes. Different from that in other species, half of the watermelon HSP20s were repressed by heat stress. Plant HSP20s displayed diverse responses to different virus infections and most of the ClHSP20s were generally repressed by Cucumber green mottle mosaic virus (CGMMV). Some ClHSP20s exhibited similar transcriptional responses to abscisic acid, melatonin, and CGMMV. Subcellular localization analyses of six selected HSP20- green fluorescence protein fusion proteins revealed diverse subcellular targeting. Some ClHSP20 proteins were affected by CGMMV, as reflected by changes in the size, number, and distribution of fluorescent granules. These systematic analyses provide a foundation for elucidating the physiological functions and biological roles of the watermelon HSP20 gene family.

Chloroplast Proteome of Nicotiana benthamiana Infected by Tomato Blistering Mosaic Virus

Tymovirus is a genus of plant pathogenic viruses that infects several dicotyledonous plants worldwide, causing serious diseases in economically important crops. The known cytopathic effect on the host cell organelles involves chloroplast membrane deformation and the induction of vesicles in its periphery. These vesicles are known to be the location where tymoviral genomic RNA replication occurs. Tomato blistering mosaic virus (ToBMV) is a tymovirus recently identified in tomato plants in Brazil, which is able to infect several other plants, including tobacco. In this work, we investigated the chloroplast proteomic profile of ToBMV-infected N. benthamiana using bidimensional electrophoresis (2-DE) and mass spectrometry, aiming to study the virus-host interaction related to the virus replication and infection. A total of approximately 200 spots were resolved, out of which 36 were differentially abundant. Differential spots were identified by mass spectrometry including photosynthesis-related and defense proteins. We identified proteins that may be targets of a direct interaction with viral proteins, such as ATP synthase β subunit, RNA polymerase beta-subunit, 50S ribosomal protein L6 and Trigger factor-like protein. The identification of these candidate proteins gives support for future protein-protein interaction studies to confirm their roles in virus replication and disease development.

Proteomics survey of Solanaceae family: Current status and challenges ahead

Solanaceae is one of the major economically important families of higher plants and has played a central role in human nutrition since the dawn of human civilization. Therefore, researchers have always been interested in understanding the complex behavior of Solanaceae members to identify key transcripts, proteins or metabolites, which are potentially associated with major traits. Proteomics studies have contributed significantly to understanding the physiology of Solanaceae members. A compilation of all the published reports showed that both gel-based (75%) and gel-free (25%) proteomic technologies have been utilized to establish the proteomes of different tissues, organs, and organelles under normal and adverse environmental conditions. Among the Solanaceae members, most of the research has been focused on tomato (42%) followed by potato (28%) and tobacco (20%), owing to their economic importance. This review comprehensively covers the progress made so far in the field of Solanaceae proteomics including novel methods developed to isolate the proteins from different tissues. Moreover, key proteins presented in this review can serve as a resource to select potential targets for crop improvement. We envisage that information presented in this review would enable us to design the stress tolerant plants with enhanced yields.

Levofloxacin is phytotoxic and modifies the protein profile of lupin seedlings

The toxicity of levofloxacin to yellow lupin plants was evaluated in this study. Recommended indexes of plant (roots and shoots) growth were determined and new indexes were proposed which better characterise the phytotoxicity of levofloxacin. These were, in particular, the activity of antioxidative enzymes, the content of free radicals, as well as the root protein content and the root protein profile. The results showed that levofloxacin considerably affected EC₅₀, measured as the activity of catalase in roots, and leaves (1.05 and 0.069 mM, respectively). The activity of peroxidase in the roots and the dry weight of seedlings were the least sensitive parameters (EC₅₀ was 1.8 and 1.76 mM, respectively). Units of toxicity clearly showed that the activity of catalase is a better measure of toxicity for low concentrations of the drug, and it is a better index of plant physiological state than the morphological parameters of seedlings. Moreover, levofloxacin changed the location of free radicals and the protein profile in plants. The changes in location of reactive oxygen species in roots were an important symptom of the drug toxicity to lupin seedlings. Our results have shown that the toxicity of levofloxacin was manifested mainly by changes in the protein profile. The content of the glyceraldehyde-3-phosphate dehydrogenase, 14-3-3-like protein A, expansin-B3-like precursor, fructose-bisphosphate aldolase, lipoxygenase, nucleotide-binding subunit of vacuolar ATPase and pyruvate dehydrogenase were found to decrease. On the other hand, plant exposure to levofloxacin resulted in an increase in the content of enolase, protein LlR18A, class III chitinase, ascorbate peroxidase, aspartate aminotransferase, alcohol dehydrogenase 1, leghemoglobin reductase-like 17 and heat shock cognate protein 80-like.

Microarray analysis of Arabidopsis WRKY33 mutants in response to the necrotrophic fungus Botrytis cinerea

The WRKY33 transcription factor was reported for resistance to the necrotrophic fungus Botrytis cinerea. Using microarray-based analysis, we compared Arabidopsis WRKY33 overexpressing lines and wrky33 mutant that showed altered susceptibility to B. cinerea with their corresponding wild-type plants. In the wild-type, about 1660 genes (7% of the transcriptome) were induced and 1054 genes (5% of the transcriptome) were repressed at least twofold at early stages of inoculation with B. cinerea, confirming previous data of the contribution of these genes in B. cinerea resistance. In Arabidopsis wild-type plant infected with B. cinerea, the expressions of the differentially expressed genes encoding for proteins and metabolites involved in pathogen defense and non-defense responses, seem to be dependent on a functional WRKY33 gene. The expression profile of 12-oxo-phytodienoic acid- and phytoprostane A1-treated Arabidopsis plants in response to B. cinerea revealed that cyclopentenones can also modulate WRKY33 regulation upon inoculation with B. cinerea. These results support the role of electrophilic oxylipins in mediating plant responses to B. cinerea infection through the TGA transcription factor. Future directions toward the identification of the molecular components in cyclopentenone signaling will elucidate the novel oxylipin signal transduction pathways in plant defense.

Proteometabolomic Study of Compatible Interaction in Tomato Fruit Challenged with Sclerotinia rolfsii Illustrates Novel Protein Network during Disease Progression

Fruit is an assimilator of metabolites, nutrients, and signaling molecules, thus considered as potential target for pathogen attack. In response to patho-stress, such as fungal invasion, plants reorganize their proteome, and reconfigure their physiology in the infected organ. This remodeling is coordinated by a poorly understood signal transduction network, hormonal cascades, and metabolite reallocation. The aim of the study was to explore organ-based proteomic alterations in the susceptibility of heterotrophic fruit to necrotrophic fungal attack. We conducted time-series protein profiling of Sclerotinia rolfsii invaded tomato (Solanum lycopersicum) fruit. The differential display of proteome revealed 216 patho-stress responsive proteins (PSRPs) that change their abundance by more than 2.5-fold. Mass spectrometric analyses led to the identification of 56 PSRPs presumably involved in disease progression; regulating diverse functions viz. metabolism, signaling, redox homeostasis, transport, stress-response, protein folding, modification and degradation, development. Metabolome study indicated differential regulation of organic acid, amino acids, and carbohydrates paralleling with the proteomics analysis. Further, we interrogated the proteome data using network analysis that identified two significant functional protein hubs centered around malate dehydrogenase, T-complex protein 1 subunit gamma, and ATP synthase beta. This study reports, for the first-time, kinetically controlled patho-stress responsive protein network during post-harvest storage in a sink tissue, particularly fruit and constitute the basis toward understanding the onset and context of disease signaling and metabolic pathway alterations. The network representation may facilitate the prioritization of candidate proteins for quality improvement in storage organ.

Transcriptome analysis reveals regulatory networks underlying differential susceptibility to Botrytis cinerea in response to nitrogen availability in Solanum lycopersicum

Nitrogen (N) is one of the main limiting nutrients for plant growth and crop yield. It is well documented that changes in nitrate availability, the main N source found in agricultural soils, influences a myriad of developmental programs and processes including the plant defense response. Indeed, many agronomical reports indicate that the plant N nutritional status influences their ability to respond effectively when challenged by different pathogens. However, the molecular mechanisms involved in N-modulation of plant susceptibility to pathogens are poorly characterized. In this work, we show that Solanum lycopersicum defense response to the necrotrophic fungus Botrytis cinerea is affected by plant N availability, with higher susceptibility in nitrate-limiting conditions. Global gene expression responses of tomato against B. cinerea under contrasting nitrate conditions reveals that plant primary metabolism is affected by the fungal infection regardless of N regimes. This result suggests that differential susceptibility to pathogen attack under contrasting N conditions is not only explained by a metabolic alteration. We used a systems biology approach to identify the transcriptional regulatory network implicated in plant response to the fungus infection under contrasting nitrate conditions. Interestingly, hub genes in this network are known key transcription factors involved in ethylene and jasmonic acid signaling. This result positions these hormones as key integrators of nitrate and defense against B. cinerea in tomato plants. Our results provide insights into potential crosstalk mechanisms between necrotrophic defense response and N status in plants.

Potato leafroll virus structural proteins manipulate overlapping, yet distinct protein interaction networks during infection

Potato leafroll virus (PLRV) produces a readthrough protein (RTP) via translational readthrough of the coat protein amber stop codon. The RTP functions as a structural component of the virion and as a nonincorporated protein in concert with numerous insect and plant proteins to regulate virus movement/transmission and tissue tropism. Affinity purification coupled to quantitative MS was used to generate protein interaction networks for a PLRV mutant that is unable to produce the read through domain (RTD) and compared to the known wild-type PLRV protein interaction network. By quantifying differences in the protein interaction networks, we identified four distinct classes of PLRV-plant interactions: those plant and nonstructural viral proteins interacting with assembled coat protein (category I); plant proteins in complex with both coat protein and RTD (category II); plant proteins in complex with the RTD (category III); and plant proteins that had higher affinity for virions lacking the RTD (category IV). Proteins identified as interacting with the RTD are potential candidates for regulating viral processes that are mediated by the RTP such as phloem retention and systemic movement and can potentially be useful targets for the development of strategies to prevent infection and/or viral transmission of Luteoviridae species that infect important crop species.