Response of Vitis vinifera cell cultures to Eutypa lata and Trichoderma atroviride culture filtrates: expression of defence-related genes and phenotypes

The fungal elicitor eutypine from Eutypa lata activates basal immunity through its phenolic side chains

Grapevine trunk diseases (GTDs) affect grape production and reduce vineyard longevity worldwide. Since the causative fungi also occur in asymptomatic trunks, we address disease outbreak in terms of altered chemical communication between host and endophyte. Here, we identified four chemically similar secondary metabolites secreted by the GTD-associated fungus Eutypa lata to analyse their modes of action in a grapevine cell culture of Vitis rupestris, where microtubules were tagged by GFP. Treatment with the metabolite eutypine activated defence responses, evident from extracellular alkalinisation and induction of defence genes. Eutypinol, instead, eliminated microtubules, in contrast to the other three compounds. Furthermore, we evaluated the effect of four corresponding chemical analogues of these compounds, sharing the phenolic but lacking the alkyne moiety. These analogues were able to induce similar defence responses in V. rupestris cells, albeit at reduced amplitude. Since closely related moieties differing only in details of the side groups at the phenolic ring differ significantly with respect to the response of the host cell, we propose that these fungal compounds act through a specific binding site at the membrane of grapevine cells. We corroborate this specificity by combination experiments, where the eutypine and the eutypinol analogues behave competitively with respect to the elicited responses. In summary, Eutypa lata secretes compounds that elicit host defence in a specific manner by interfering with early events of immunity signalling. This supports the notion that a real understanding of GTDs has to address inter-organismic chemical communication.

A Panoramic View on Grapevine Trunk Diseases Threats: Case of Eutypa Dieback, Botryosphaeria Dieback, and Esca Disease

Grapevine trunk diseases (GTD) are currently one of the most devastating and challenging diseases in viticulture, leading to considerable yield losses and a remarkable decline in grapevine quality. The identification of the causal agents is the cornerstone of an efficient approach to fighting against fungal diseases in a sustainable, non-chemical manner. This review attempts to describe and expose the symptoms of each pathology related to GTD, the modes of transmission, and the harmfulness of recently reported agents. Special attention was given to new diagnostic tests and technologies, grapevine defense mechanisms, molecular mechanisms of endophytes fungal colonization, and management strategies used to control these threats. The present extended review is, therefore, an updated state-of-the-art report on the progress in the management of vineyards.

Biotic and Abiotic Elicitors of Stilbenes Production in Vitis vinifera L. Cell Culture

The in vitro cell cultures derived from the grapevine (Vitis vinifera L.) have been used for the production of stilbenes treated with different biotic and abiotic elicitors. The red-grape cultivar Váh has been elicited by natural cellulose from Trichoderma viride, the cell wall homogenate from Fusarium oxysporum and synthetic jasmonates. The sodium-orthovanadate, known as an inhibitor of hypersensitive necrotic response in treated plant cells able to enhance production and release of secondary metabolite into the cultivation medium, was used as an abiotic elicitor. Growth of cells and the content of phenolic compounds trans-resveratrol, trans-piceid, δ-viniferin, and ɛ-viniferin, were analyzed in grapevine cells treated by individual elicitors. The highest accumulation of analyzed individual stilbenes, except of trans-piceid has been observed after treatment with the cell wall homogenate from F. oxysporum. Maximum production of trans-resveratrol, δ- and ɛ-viniferins was triggered by treatment with cellulase from T. viride. The accumulation of trans-piceid in cell cultures elicited by this cellulase revealed exactly the opposite effect, with almost three times higher production of trans-resveratrol than that of trans-piceid. This study suggested that both used fungal elicitors can enhance production more effectively than commonly used jasmonates.

Hunting modulators of plant defence: the grapevine trunk disease fungus Eutypa lata secretes an amplifier for plant basal immunity

Grapevine trunk diseases (GTDs) are progressively affecting vineyard longevity and productivity worldwide. To be able to understand and combat these diseases, we need a different concept of the signals exchanged between the grapevine and fungi than the well-studied pathogen-associated molecular pattern and effector concepts. We screened extracts from fungi associated with GTDs for their association with basal defence responses in suspension cells of grapevine. By activity-guided fractionation of the two selected extracts, O-methylmellein was identified as a candidate modulator of grapevine immunity. O-Methylmellein could not induce immune responses by itself (i.e. does not act as an elicitor), but could amplify some of the defence responses triggered by the bacterial elicitor flg22, such as the induction level of defence genes and actin remodelling. These findings show that Eutypa lata, exemplarily selected as an endophytic fungus linked with GTDs, can secrete compounds that act as amplifiers of basal immunity. Thus, in addition to elicitors that can trigger basal immunity, and effectors that down-modulate antibacterial basal immunity, once it had been activated, E. lata seems to secrete a third type of chemical signal that amplifies basal immunity and may play a role in the context of consortia of mutually competing microorganisms.

Impact of Paraburkholderia phytofirmans PsJN on Grapevine Phenolic Metabolism

Phenolic compounds are implied in plant-microorganisms interaction and may be induced in response to plant growth-promoting rhizobacteria (PGPRs). Among PGPR, the beneficial bacterium Paraburkholderia phytofirmans PsJN was previously described to stimulate the growth of plants and to induce a better adaptation to both abiotic and biotic stresses. This study aimed to investigate the impact of PsJN on grapevine secondary metabolism. For this purpose, gene expression (qRT-PCR) and profiling of plant secondary metabolites (UHPLC-UV/DAD-MS QTOF) from both grapevine root and leaves were compared between non-bacterized and PsJN-bacterized grapevine plantlets. Our results showed that PsJN induced locally (roots) and systemically (leaves) an overexpression of PAL and STS and specifically in leaves the overexpression of all the genes implied in phenylpropanoid and flavonoid pathways. Moreover, the metabolomic approach revealed that relative amounts of 32 and 17 compounds in roots and leaves, respectively, were significantly modified by PsJN. Once identified to be accumulated in response to PsJN by the metabolomic approach, antifungal properties of purified molecules were validated in vitro for their antifungal effect on Botrytis cinerea spore germination. Taking together, our findings on the impact of PsJN on phenolic metabolism allowed us to identify a supplementary biocontrol mechanism developed by this PGPR to induce plant resistance against pathogens.

Tal6 From Trichoderma atroviride Is a LysM Effector Involved in Mycoparasitism and Plant Association

LysM effectors play a relevant role during the plant colonization by successful phytopathogenic fungi, since they enable them to avoid either the triggering of plant defense mechanisms or their attack effects. Tal6, a LysM protein from Trichoderma atroviride, is capable of binding to complex chitin. However, until now its biological function is not completely known, particularly its participation in plant–Trichoderma interactions. We obtained T. atroviride Tal6 null mutant and Tal6 overexpressing strains and determined the role played by this protein during Trichoderma-plant interaction and mycoparasitism. LysM effector Tal6 from T. atroviride protects the hyphae from chitinases by binding to chitin of the fungal cell wall, increases the fungus mycoparasitic capacity, and modulates the activation of the plant defense system. These results show that beneficial fungi also employ LysM effectors to improve their association with plants.

Biotechnological Potential of LSD1, EDS1, and PAD4 in the Improvement of Crops and Industrial Plants

Lesion Simulating Disease 1 (LSD1), Enhanced Disease Susceptibility (EDS1) and Phytoalexin Deficient 4 (PAD4) were discovered a quarter century ago as regulators of programmed cell death and biotic stress responses in Arabidopsis thaliana. Recent studies have demonstrated that these proteins are also required for acclimation responses to various abiotic stresses, such as high light, UV radiation, drought and cold, and that their function is mediated through secondary messengers, such as salicylic acid (SA), reactive oxygen species (ROS), ethylene (ET) and other signaling molecules. Furthermore, LSD1, EDS1 and PAD4 were recently shown to be involved in the modification of cell walls, and the regulation of seed yield, biomass production and water use efficiency. The function of these proteins was not only demonstrated in model plants, such as Arabidopsis thaliana or Nicotiana benthamiana, but also in the woody plant Populus tremula x tremuloides. In addition, orthologs of LSD1, EDS1, and PAD4 were found in other plant species, including different crop species. In this review, we focus on specific LSD1, EDS1 and PAD4 features that make them potentially important for agricultural and industrial use.

Comparison of the Molecular Responses of Tolerant, Susceptible and Highly Susceptible Grapevine Cultivars During Interaction With the Pathogenic Fungus Eutypa lata

Eutypa lata is the causal agent of eutypa dieback, one of the most destructive grapevine trunk disease that causes severe economic losses in vineyards worldwide. This fungus causes brown sectorial necrosis in wood which affect the vegetative growth. Despite intense research efforts made in the past years, no cure currently exists for this disease. Host responses to eutypa dieback are difficult to address because E. lata is a wood pathogen that causes foliar symptoms several years after infection. With the aim to classify the level of susceptibility of grapevine cultivars to the foliar symptoms caused by E. lata, artificial inoculations of Merlot, Cabernet Sauvignon, and Ugni Blanc were conducted over 3 years. Merlot was the most tolerant cultivar, whereas Ugni Blanc and Cabernet Sauvignon exhibited higher and differential levels of susceptibility. We took advantage of their contrasting phenotypes to explore their defense responses, including the activation of pathogenesis-related (PR) genes, oxylipin and phenylpropanoid pathways and the accumulation of stilbenes. These analyses were carried out using the millicell system that enables the molecular dialogue between E. lata mycelium and grapevine leaves to take place without physical contact. Merlot responded to E. lata by inducing the expression of a large number of defense-related genes. On the contrary, Ugni Blanc failed to activate such defense responses despite being able to perceive the fungus. To gain insight into the role of carbon partitioning in E. lata infected grapevine, we monitored the expression of plant genes involved in sugar transport and cleavage, and measured invertase activities. Our results evidence a coordinated up-regulation of VvHT5 and VvcwINV genes, and a stimulation of the cell wall invertase activity in leaves of Merlot elicited by E. lata, but not in Ugni Blanc. Altogether, this study indicates that the degree of cultivar susceptibility is associated with the activation of host defense responses, including extracellular sucrolytic machinery and hexose uptake during the grapevine/E. lata interaction. Given the role of these activities in governing carbon allocation through the plant, we postulate that the availability of sugar resources for either the host or the fungus is crucial for the outcome of the interaction.

Transcriptional response of grapevine to infection with the fungal pathogen Lasiodiplodia theobromae

Botryosphaeria dieback on the grapevine is caused by Botryosphaeriaceae fungi, which threatens the yield and quality of grapes. At present, chemical control strategies are often observed to be ineffective in controlling the disease worldwide. Improving our understanding of the molecular mechanisms that confer resistance to pathogens would facilitate the development of more pathogen-tolerant grape varieties. Here, we used RNA sequencing analysis to profile the transcriptome of grapevine green shoots infected with Lasiodiplodia theobromae over a time course of 4, 8 and 12 hours post inoculation. A total of 5181 genes were identified as differentially expressed genes (DEGs), and DEGs were more abundant over time. Further analysis revealed that many of these DEGs are involved in plant-pathogen interactions, hormone signal transduction and phenylpropanoid biosynthesis pathways, suggesting that innate immunity, phytohormone signaling and many phenylpropanoid compounds, which constitute a complex defense network in plants, are involved in the response of grapevine against to L. theobromae infection. This study provides novel insights into the molecular mechanisms of plant-pathogen interactions that will be valuable for the genetic improvement of grapevines.

Secreted proteins produced by fungi associated with Botryosphaeria dieback trigger distinct defense responses in Vitis vinifera and Vitis rupestris cells

Grapevine trunk diseases (Eutypa dieback, esca and Botryosphaeria dieback) are caused by a complex of xylem-inhabiting fungi, which severely reduce yields in vineyards. Botryosphaeria dieback is associated with Botryosphaeriaceae. In order to develop effective strategies against Botryosphaeria dieback, we investigated the molecular basis of grapevine interactions with a virulent species, Neofusicoccum parvum, and a weak pathogen, Diplodia seriata. We investigated defenses induced by purified secreted fungal proteins within suspension cells of Vitis (Vitis rupestris and Vitis vinifera cv. Gewurztraminer) with putative different susceptibility to Botryosphaeria dieback. Our results show that Vitis cells are able to detect secreted proteins produced by Botryosphaeriaceae, resulting in a rapid alkalinization of the extracellular medium and the production of reactive oxygen species. Concerning early defense responses, N. parvum proteins induced a more intense response compared to D. seriata. Early and late defense responses, i.e., extracellular medium alkalinization, cell death, and expression of PR defense genes were stronger in V. rupestris compared to V. vinifera, except for stilbene production. Secreted Botryosphaeriaceae proteins triggered a high accumulation of δ-viniferin in V. vinifera suspension cells. Artificial inoculation assays on detached canes with N. parvum and D. seriata showed that the development of necrosis is reduced in V. rupestris compared to V. vinifera cv. Gewurztraminer. This may be related to a more efficient induction of defense responses in V. rupestris, although not sufficient to completely inhibit fungal colonization. Overall, our work shows a specific signature of defense responses depending on the grapevine genotype and the fungal species.