Abstract
Promoter-probe vectors carrying fluorescent protein-reporter genes are powerful tools used to study microbial ecology, epidemiology, and etiology. In addition, they provide direct visual evidence of molecular interactions related to cell physiology and metabolism. Knowledge and advances carried out thanks to the construction of soft-rot Pectobacteriaceae biosensors, often inoculated in potato Solanum tuberosum, are discussed in this review. Under epifluorescence and confocal laser scanning microscopies, Dickeya and Pectobacterium-tagged strains managed to monitor in situ bacterial viability, microcolony and biofilm formation, and colonization of infected plant organs, as well as disease symptoms, such as cell-wall lysis and their suppression by biocontrol antagonists. The use of dual-colored reporters encoding the first fluorophore expressed from a constitutive promoter as a cell tag, while a second was used as a regulator-based reporter system, was also used to simultaneously visualize bacterial spread and activity. This revealed the chronology of events leading to tuber maceration and quorum-sensing communication, in addition to the disruption of the latter by biocontrol agents. The promising potential of these fluorescent biosensors should make it possible to apprehend other activities, such as subcellular localization of key proteins involved in bacterial virulence in planta, in the near future.
Highlights
Soft-rot Pectobacteriaceae (SRP) [1] consist of the bacterial genera Pectobacterium and Dickeya, whose members are responsible for a wide spectrum of soft-rot diseases of agriculturally important vegetable crops and ornamental plants worldwide [2,3,4]
The ecological niches of SRP bacteria are various; they can be isolated from plant, bulk and/or rhizosphere soil [14], surface and ground water, such as the most recently defined novel species Dickeya lacustris and Dickeya undicola [6,15,16], and on the surface and interior of insects [17,18,19]
Another example of the application of green fluorescent protein (GFP)-tagged potential biocontrol agent (BCA) against soft-rot pathogens is a recent study by Cui et al [120], in which the Bacillus amyloliquefaciens KC-1 strain was used to control P. carotovorum subsp. carotovorum on Chinese cabbage in vitro and in planta
Summary
Soft-rot Pectobacteriaceae (SRP) [1] consist of the bacterial genera Pectobacterium and Dickeya, whose members are responsible for a wide spectrum of soft-rot diseases of agriculturally important vegetable crops and ornamental plants worldwide [2,3,4]. SRP bacteria may invade surrounding plants via wound sites or natural openings, such as lenticels or stomata, causing latent infection without developing disease symptoms [4] During this hidden phase of the infection cycle, bacteria can survive in a dormant state for a long time inside vascular or parenchymatous tissues, representing the most important source of disease inoculum [23,24,25,26], but not the sole mode of transmission according to spatial analysis of blackleg-affected seed potato crops in Scotland [27]. When certain environmental conditions (high humidity, fresh or mild temperatures, and poor oxygen availability) become favorable for plant disease, Dickeya and Pectobacterium species undergo a transition from latent to pathogenic [14] This pathogenic phase is characterized by rapid bacterial multiplication and the production of numerous extracellular lytic enzymes, involved in invading and destroying plant tissues, responsible for the necrotrophic lifestyle of these pathogens [30,31]. Main Traits of Fluorescent Proteins Used to Construct Tagged-Soft-Rot Pectobacteriaceae
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