Mqo, a Tricarboxylic Acid Cycle Enzyme, Is Required for Virulence of Pseudomonas syringae pv. tomato Strain DC3000 on Arabidopsis thaliana

Abstract

Plant pathogenic bacteria, such as Pseudomonas syringae pv. tomato strain DC3000, the causative agent of tomato bacterial speck disease, grow to high levels in the apoplastic space between plant cells. Colonization of plant tissue requires expression of virulence factors that modify the apoplast to make it more suitable for pathogen growth or facilitate adaptation of the bacteria to the apoplastic environment. To identify new virulence factors involved in these processes, DC3000 Tn5 transposon insertion mutants with reduced virulence on Arabidopsis thaliana were identified. In one of these mutants, the Tn5 insertion disrupted the malate:quinone oxidoreductase gene (mqo), which encodes an enzyme of the tricarboxylic acid cycle. mqo mutants do not grow to wild-type levels in plant tissue at early time points during infection. Further, plants infected with mqo mutants develop significantly reduced disease symptoms, even when the growth of the mqo mutant reaches wild-type levels at late stages of infection. Mutants lacking mqo function grow more slowly in culture than wild-type bacteria when dicarboxylates are the only available carbon source. To explore whether dicarboxylates are important for growth of DC3000 in the apoplast, we disrupted the dctA1 dicarboxylate transporter gene. DC3000 mutants lacking dctA1 do not grow to wild-type levels in planta, indicating that transport and utilization of dicarboxylates are important for virulence of DC3000. Thus, mqo may be required by DC3000 to meet nutritional requirements in the apoplast and may provide insight into the mechanisms underlying the important, but poorly understood process of adaptation to the host environment.

Genomic Analysis of the Kiwifruit Pathogen Pseudomonas syringae pv. actinidiae Provides Insight into the Origins of an Emergent Plant Disease

“…Pseudomonas has a preference for growth on TCA cycle intermediates and dctA1 a dicarboxylate transporter gene is important for the virulence of Pto DC3000 [86]. It is possible that the putative T3SS-targeted di-carboxylic acid transporter, enters the plant cell and incorporates into a host cell membranes to facilitate export of this sugar acid in a manner analogous to that recently suggested for á keto glutarate in Xanthomonas oryzae pv.…”

Ketoglutarate Transport Protein KgtP Is Secreted through the Type III Secretion System and Contributes to Virulence in Xanthomonas oryzae pv. oryzae

“…2 and 6). The dicarboxylate transport (DctA) system for the uptake of C 4 -dicarboxylates (i.e., oxaloacetate, malate, fumarate, and succinate) has been intensively studied in some bacteria (14,30,68). However, little is known about the DctA system in Xanthomonas, despite DCAs being the principal and preferred carbon sources during infection (54,61).…”

“…KgtP is responsible for transferring TCA cycle intermediates and maintaining the concentrations of dicarboxylic acid (14,30,68); consequently, we speculated that the kgtP mutant might be impaired for growth on selected carbon sources.…”

“…A mutation in the DctA system in Pseudomonas syringae pv. tomato had a partial effect on bacterial growth and virulence in planta (30), indicating that other uptake systems also function in nutrient acquisition.…”

Phosphoglycerate Kinase Is Involved in Carbohydrate Utilization, Extracellular Polysaccharide Biosynthesis, and Cell Motility of Xanthomonas axonopodis pv. glycines Independent of Clp

“…oryzicola (Xoc), which infects rice (Guo et al, 2017). Results of these studies have shown that carbohydrate acquisition is essential for the pathogen to grow and establish a successful infection within the hosts (Tang et al, 2005;Mellgren et al, 2009). When the pathogen gains entry into the host plant, it first propagates in the apoplastic space until reaching a density threshold, followed by the expression of lots of virulence-related genes and secretion of cell-wall degrading enzymes through the diffusible signal factor (DSF)-mediated QS mechanism (Büttner and Bonas, 2010).…”