Contribution of the Regulatory Gene lemA to Field Fitness of Pseudomonas syringae pv. syringae

Abstract

In Pseudomonas syringae pv. syringae, lemA is required for brown spot lesion formation on snap bean and for production of syringomycin and extracellular proteases (. Plant-Microbe Interact. 3:149-156, 1990). The lemA mutant NPS3136 (lemA1::Tn5) was previously found to be indistinguishable from its pathogenic parent B728a in its ability to grow when infiltrated into bean leaves of plants maintained under controlled environmental conditions (Willis et al., Mol. Plant-Microbe Interact. 3:149-156, 1990). We compared population sizes of NPS3136 and B728aN (a Nal r clone of wild-type B728a) in two field experiments to determine the effect of inactivation of lemA on the fitness of P. syringae pv. syringae. In one experiment, the bacterial strains were spray inoculated onto the foliage of 25-day-old bean plants. In the other, seeds were inoculated at the time of planting. In both experiments, the strains were inoculated individually and coinoculated in a 1:1 ratio. NPS3136 and B728aN achieved similar large population sizes on germinating seeds. However, in association with leaves, population sizes of NPS3136 were diminished relative to those of B728aN in both experiments. Thus, lemA contributed significantly to the fitness of P. syringae pv. syringae in association with bean leaves but not on germinating seeds under field conditions. When NPS3136 was coinoculated with B728aN, the mutant behaved as it did when inoculated alone. However, population sizes of B728aN in the coinoculation treatment were much lower than those when it was inoculated alone. Inactivation of the lemA gene appeared to have rendered the mutant suppressive to B728aN.

Pseudomonas syringae pv. tomato DC3000 HopPtoM (CEL ORF3) is important for lesion formation but not growth in tomato and is secreted and translocated by the Hrp type III secretion system in a chaperone‐dependent manner

“…However, it is important to note that gacS does contribute significantly to the fitness of P. syringae pv. syringae B728 in the bean field (Hirano et al, 1997), and it is possible that the elicitation of lesions by HopPtoM may similarly confer some benefit to P. syringae pv. tomato in the tomato field, for example, in promoting dissemination of inoculum.…”

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“…A similar, possibly related, phenomenon has been observed in populations of P. syringae pv. syringae growing on bean leaves where a gacS mutant appeared to render the wild-type less fit to survive (Hirano et al 1997).…”

Swarming by Pseudomonas syringae B728a Requires gacS ( lemA ) and gacA but Not the Acyl-Homoserine Lactone Biosynthetic Gene ahlI

“…syringae B728a, a causal agent of bacterial brown spot on beans (Phaseolus vulgaris), gacS and gacA mutants are deficient in the production of syringomycin, N-acyl-L-homoserine lactone (acyl-HSL), extracellular protease, and necrotic lesions (16). The ability of these mutants to persist in a field setting is also greatly reduced, although the bacteria appear to grow nearly as well as the wild type in planta (13). In this report, we add conditional swarming to the list of gacS gacA phenotypes in B728a.…”