Ralstonia solanacearum Extracellular Polysaccharide Is a Specific Elicitor of Defense Responses in Wilt-Resistant Tomato Plants

Abstract

Ralstonia solanacearum, which causes bacterial wilt of diverse plants, produces copious extracellular polysaccharide (EPS), a major virulence factor. The function of EPS in wilt disease is uncertain. Leading hypotheses are that EPS physically obstructs plant water transport, or that EPS cloaks the bacterium from host plant recognition and subsequent defense. Tomato plants infected with R. solanacearum race 3 biovar 2 strain UW551 and tropical strain GMI1000 upregulated genes in both the ethylene (ET) and salicylic acid (SA) defense signal transduction pathways. The horizontally wilt-resistant tomato line Hawaii7996 activated expression of these defense genes faster and to a greater degree in response to R. solanacearum infection than did susceptible cultivar Bonny Best. However, EPS played different roles in resistant and susceptible host responses to R. solanacearum. In susceptible plants the wild-type and eps− mutant strains induced generally similar defense responses. But in resistant Hawaii7996 tomato plants, the wild-type pathogens induced significantly greater defense responses than the eps− mutants, suggesting that the resistant host recognizes R. solanacearum EPS. Consistent with this idea, purified EPS triggered significant SA pathway defense gene expression in resistant, but not in susceptible, tomato plants. In addition, the eps− mutant triggered noticeably less production of defense-associated reactive oxygen species in resistant tomato stems and leaves, despite attaining similar cell densities in planta. Collectively, these data suggest that bacterial wilt-resistant plants can specifically recognize EPS from R. solanacearum.

RETRACTED: <i>Induction of Systemic Resistance in Tomato against Ralstonia solanacearum by Pseudomonas fluorescens</i>

“…Bacterial wilt caused by Ralstonia solanacearum is contemplated to be one of the most important plant diseases in tropical agriculture [1] [2]. It has a large host range of more than 200 species in 50 families [3].…”

The awr Gene Family Encodes a Novel Class of Ralstonia solanacearum Type III Effectors Displaying Virulence and Avirulence Activities

“…DC3000 derivative lacking the conserved effector locus instead of the wild type (not shown). Other studies have shown disparate responses of effector proteins on Arabidopsis and tomato plants (Lin et al 2008;Milling et al 2011). Unsurprisingly, Arabidopsis is a tremendous source of plant resistance toward pathogens and its study led to the discovery of the R protein, RRS1 (resistance to R. solanacearum 1) that confers resistance to R. solanacearum expressing PopP2 (Deslandes et al 2003).…”

In Vitro Evaluation of Antibacterial Chemicals and Bioagents against Ralstonia solanacearum Infecting Bacterial Wilt in Ginger

“…Bacterial wilt caused by R. solanacearum is deemed to be one of the most important plant diseases in tropical agriculture (Hayward, 1990;Milling et al, 2011). It has a large host range of more than 200 species in 50 families (Aliye et al, 2008).…”