Dynamic expression of Ralstonia solanacearum virulence factors and metabolism-controlling genes during plant infection

Abstract

Background Ralstonia solanacearum is the causal agent of bacterial wilt, a devastating plant disease responsible for serious economic losses especially on potato, tomato, and other solanaceous plant species in temperate countries. In R. solanacearum, gene expression analysis has been key to unravel many virulence determinants as well as their regulatory networks. However, most of these assays have been performed using either bacteria grown in minimal medium or in planta, after symptom onset, which occurs at late stages of colonization. Thus, little is known about the genetic program that coordinates virulence gene expression and metabolic adaptation along the different stages of plant infection by R. solanacearum. Results We performed an RNA-sequencing analysis of the transcriptome of bacteria recovered from potato apoplast and from the xylem of asymptomatic or wilted potato plants, which correspond to three different conditions (Apoplast, Early and Late xylem). Our results show dynamic expression of metabolism-controlling genes and virulence factors during parasitic growth inside the plant. Flagellar motility genes were especially up-regulated in the apoplast and twitching motility genes showed a more sustained expression in planta regardless of the condition. Xylem-induced genes included virulence genes, such as the type III secretion system (T3SS) and most of its related effectors and nitrogen utilisation genes. The upstream regulators of the T3SS were exclusively up-regulated in the apoplast, preceding the induction of their downstream targets. Finally, a large subset of genes involved in central metabolism was exclusively down-regulated in the xylem at late infection stages. Conclusions This is the first report describing R. solanacearum dynamic transcriptional changes within the plant during infection. Our data define four main genetic programmes that define gene pathogen physiology during plant colonisation. The described expression of virulence genes, which might reflect bacterial states in different infection stages, provides key information on the R. solanacearum potato infection process.

NorA, HmpX, and NorB Cooperate to Reduce NO Toxicity during Denitrification and Plant Pathogenesis in Ralstonia solanacearum

“…Rs draws on its broad repertoire of metabolic capabilities to survive in soil and water, invade plant roots, and colonize and obstruct its host’s water-transporting xylem vessels ( 3 ). The pathogen’s metabolism adapts rapidly as it transitions among diverse microniches in surface water, in soil, and inside hosts ( 4 – 6 ). Plant xylem vessels, the primary in-host habitat of Rs , contain little oxygen but have substantial levels of nitrate (NO 3 ), around 30 mM ( 7 ).…”

NorA, HmpX, and NorB cooperate to reduce NO toxicity during denitrification and plant pathogenesis in Ralstonia solanacearum

“…Rs draws on its broad repertoire of metabolic capabilities to survive in soil and water, invade plant roots, and colonize and obstruct its host's water-transporting xylem vessels (3). The pathogen's metabolism adapts rapidly as it transitions among diverse micro-niches in surface water, soil, and inside hosts (4,5). Plant xylem vessels, the primary in-host habitat of Rs, contain little oxygen but have substantial levels of nitrate (NO 3 ), around 30 mM (6).…”

A Breach in Plant Defences: Pseudomonas syringae pv. actinidiae Targets Ethylene Signalling to Overcome Actinidia chinensis Pathogen Responses

“…Thus, the ability to produce ethylene may contribute to Psa virulence, as it does for other P. syringae pathovars, such as pvs. glycinea and phaseolicola [ 9 , 39 ], as well as for Ralstonia solanacearum strains [ 40 , 41 ]. In the latter species, ethylene production is coregulated with the type 3 secretion system, suggesting its function in pathogenesis.…”