Dickeya dadantii pectic enzymes necessary for virulence are also responsible for activation of the Arabidopsis thaliana innate immune system

Abstract

Soft-rot diseases of plants attributed to Dickeya dadantii result from lysis of the plant cell wall caused by pectic enzymes released by the bacterial cell by a type II secretion system (T2SS). Arabidopsis thaliana can express several lines of defence against this bacterium. We employed bacterial mutants with defective envelope structures or secreted proteins to examine early plant defence reactions. We focused on the production of AtrbohD-dependent reactive oxygen species (ROS), callose deposition and cell death as indicators of these reactions. We observed a significant reduction in ROS and callose formation with a bacterial mutant in which genes encoding five pectate lyases (Pels) were disrupted. Treatment of plant leaves with bacterial culture filtrates containing Pels resulted in ROS and callose production, and both reactions were dependent on a functional AtrbohD gene. ROS and callose were produced in response to treatment with a cellular fraction of a T2SS-negative mutant grown in a Pels-inducing medium. Finally, ROS and callose were produced in leaves treated with purified Pels that had also been shown to induce the expression of jasmonic acid-dependent defence genes. Pel catalytic activity is required for the induction of ROS accumulation. In contrast, cell death observed in leaves infected with the wild-type strain appeared to be independent of a functional AtrbohD gene. It was also independent of the bacterial production of pectic enzymes and the type III secretion system (T3SS). In conclusion, the work presented here shows that D. dadantii is recognized by the A. thaliana innate immune system through the action of pectic enzymes secreted by bacteria at the site of infection. This recognition leads to AtrbohD-dependent ROS and callose accumulation, but not cell death.

Plant Soft Rot Development and Regulation from the Viewpoint of Transcriptomic Profiling

“…According to the transcript profile, the action of RBOH seems to be the major source of ROS during Pba -caused infection. This is in accordance with a previous study showing that oxidative burst in Dickeya -infected Arabidopsis is mainly generated via the expression of AtRBOH independently of the SA-mediated responses [ 71 ]. A major portion of the DEGs related to antioxidant systems encodes glutathione metabolic enzymes.…”

Oligogalacturonide production upon Arabidopsis thaliana – Botrytis cinerea interaction

“…In conclusion, this study provides an extension of the omics toolbox with a method for the global analysis of the OGs that are produced during plant-pathogen interactions. This method will allow the study of other cell wall-derived signaling molecules involved in development and in abiotic stress responses, to investigate the evolution of enzymatic interactions between plants and their microbial environment, and may lead to the development of new strategies for the protection of crops against pathogens (36).…”

Pectin Oligosaccharides Ameliorate Colon Cancer by Regulating Oxidative Stress- and Inflammation-Activated Signaling Pathways

“…The oligosaccharides produced in digestive tracts will promote the production of volatile fatty acids, which can release constipation, reduce serum blood glucose, improve mineral absorption and lipid metabolism, prevent colonic cancer, inhibit pathogen adhesion, and modulate immune activity. Pectin oligosaccharides (POS) belong to new potential prebiotics with various health-promoting effects ( 7 , 8 ), such as against Shiga toxins ( 9 ) and pathogen binding ( 10 ), induction of apoptosis of human colonic adenocarcinoma cells ( 11 ), immunomodulation ( 12 , 13 ), and cardiovascular protection ( 14 ). Long-term pectin consumption has been found to suppress weight gain and reduce obesity risk in an animal obesity model ( 15 ).…”