Caffeic Acid in Tobacco Root Exudate Defends Tobacco Plants From Infection by Ralstonia solanacearum

Abstract

In rhizospheres, chemical barrier-forming natural compounds play a key role in preventing pathogenic bacteria from infecting plant roots. Here, we sought to identify specific phenolic exudates in tobacco (Nicotiana tobaccum) plants infected by the soil-borne pathogen Ralstonia solanacearum that may exhibit antibacterial activity and promote plant resistance against pathogens. Among detected phenolic acids, only caffeic acid was significantly induced in infected plants by R. solanacearum relative to healthy plants, and the concentration of caffeic acid reached 1.95 μg/mL. In vivo, caffeic acid at 200 μg/mL was highly active against R. solanacearum and obviously damaged the membrane structure of the R. solanacearum cells, resulting in the thinning of the cell membrane and irregular cavities in cells. Moreover, caffeic acid significantly inhibited biofilm formation by repressing the expression of the lecM and epsE genes. In vitro, caffeic acid could effectively activate phenylalanine ammonia-lyase (PAL) and peroxidase (POD) and promote the accumulation of lignin and hydroxyproline. In pot and field experiments, exogenous applications of caffeic acid significantly reduced and delayed the incidence of tobacco bacterial wilt. Taken together, all these results suggest that caffeic acid played a crucial role in defending against R. solanacearum infection and was a potential and effective antibacterial agent for controlling bacterial wilt.

The Role of Hydroxycinnamic Acid Amide Pathway in Plant Immunity

“…In addition, caffeic acid can also inhibit biofilm formation by inhibiting the expression of lecM and epsE genes. Exogenous caffeic acid also effectively activated peroxidase and PAL ( Li et al, 2021b ). Sinapic acid was chemically studied as a cinnamic acid derivative and also inhibited the growth, conidial germination of F. oxysporum and reduced the activity of pathogenic enzymes at high doses ( Wu et al, 2009 ).…”

Multivariate divergence in wild microbes: no evidence for evolution along a genetic line of least resistance

“…Caffeic acid is a common metabolite produced by many plants as a precursor in the production of lignin and is also known to directly inhibit the growth of several bacteria and fungi (Ravn et al ., 1989), suggesting it has potential to act as a defense compound both through strengthening plant cell walls and inhibiting microbial colonization of plant tissues. In tobacco, bacterial pathogens induce caffeic acid secretion in root exudates (Li et al ., 2021), and fungal colonization of barley plants induces the secretion of fungitoxic biochemical derivatives of caffeic acid (Lanoue et al ., 2010).…”

“…In tobacco, bacterial pathogens induce caffeic acid secretion in root exudates (Li et al, 2021), and fungal colonization of barley plants induces the secretion of fungitoxic biochemical derivatives of caffeic acid (Lanoue et al, 2010).…”

Seaweed-Derived Phenolic Compounds in Growth Promotion and Stress Alleviation in Plants

“…According to Li [ 96 ] exogenous application of caffeic acid inhibited Ralstonia solanacearum infection in tobacco plants by preventing the expression of epsE and lecM genes and the formation of biofilms. In vitro, caffeic acid enhanced the activity of the enzyme phenylalanine ammonia-lyase and peroxidase, which led to the accumulation of hydroxyproline and lignin.…”