Seeking an apoplastic stomatal dysregulation factor - Bioassay guided fractionation and proteomic analysis of apoplastic fluids from Vitis vinifera leaves infected by Plasmopara viticola

Impact of Plasmopara viticola on starch metabolism and stomachal functions in grapevine leaves

The grapevine downy mildew affects leaves and young berries and can affect the harvest quality and quantity. The causal agent is the obligate biotroph oomycete Plasmopara viticola that induces severe physiological alterations in infected leaves. One is the abnormal accumulation of starch in oil spots, the characteristic symptoms of the disease. Another is a deregulation of stomatal movements. Stomata, natural openings on the leaf surface allowing gas exchanges between the plant and the atmosphere, stay abnormally open during the night and do no longer close upon water stress or ABA treatment in infected leaves. This thesis is divided into two chapters that aim to i) explain the origin and m…

Activation of Grapevine Defense Mechanisms: Theoretical and Applied Approaches

part 4.; International audience; Grapevine, as other plants, possesses an innate immune system that usually prevents infection by pathogens. General elicitors are compounds of different biochemical families capable of inducing plant defense reactions. In grapevine, the cascade of defense events induced by elicitors has been studied among others in cell suspensions. The perception of the elicitor triggers signaling events that allow the activation of defense genes encoding PR proteins and other proteins involved in phytoalexin production and cell wall reinforcement. The grapevine phytoalexins resveratrol and derivated compounds have been largely studied. In addition to their antimicrobial ac…

Changes in carbohydrate metabolism in Plasmopara viticola-infected grapevine leaves.

International audience; The oomycete Plasmopara viticola is responsible for downy mildew, a severe grapevine disease. In infected grapevine leaves, we have observed an abnormal starch accumulation at the end of the dark period, suggesting modifications in starch metabolism. Therefore, several complementary approaches, including transcriptomic analyses, measurements of enzyme activities, and sugar quantification, were performed in order to investigate and to understand the effects of P. viticola infection on leaf starch and-to a larger extent-carbohydrate metabolism. Our results indicate that starch accumulation is associated with an increase in ADP-glucose pyrophosphorylase (AGPase) activit…

How Plasmopara viticola is able to alter grapevine leaf physiology

National audience

Trehalose and trehalose-6-phosphate induce stomatal movements and interfere with ABA-induced stomatal closure in grapevine

Aims: The effects of trehalose and trehalose-6-phosphate (T6P), among other sugars, were assessed on grapevine stomatal movements. Methods and results: Epidermal peels were used to assess the effects of sugars. Low concentrations of trehalose and T6P (1 μM) induced an osmotic-independent reduction of the stomatal aperture in light conditions. Furthermore, ABA-induced stomatal closure was reduced by sugar application in association with lower accumulation of reactive oxygen species in guard cells. Similar effects, although weaker, were observed in response to the disaccharides sucrose and maltose, but not in response to the monosaccharides fructose and glucose. Conclusion: This study clearly…

Toward the Identification of Two Glycoproteins Involved in the Stomatal Deregulation of Downy Mildew–Infected Grapevine Leaves

SPE Pôle IPM UB; International audience; Stomata remain abnormally opened and unresponsive to abscisic acid in grapevine leaves infected by downy mildew. This deregulation occurs from 3 days post inoculation and increases concomitantly with leaf colonization by the pathogen. Using epidermal peels, we demonstrated that the active compound involved in this deregulation is located in the apoplast. Biochemical assays showed that the active compound present in the apoplastic fluids isolated from Plasmopara viticola infected grapevine leaves (IAF) is a CysCys bridge-independent, thermostable and glycosylated protein. Fractionation guided assays based on chromatography / stomatal response and prot…