Chemoreceptors are essential proteins able to detect environmental changes for
bacterial adaptation to the environment. The genes encoding these proteins are
found individually in the genome or forming clusters with other genes related to
chemotaxis. In plant-pathogenic bacteria, about 82 thousand chemosensory
sequences have been described (1). In the Pseudomonas syringae complex, one
of the most important groups of plant-pathogenic bacteria, four chemotaxisrelated
clusters have been described. However, one of these clusters, named
cluster II, is absent in some bacteria of this complex infecting woody hosts of the
Apocinaceae family. Examples of the absence of this cluster are strains of
Pseudomonas savastanoi pv. mandevillae (Psm) and some strains of P.
savastanoi pv. nerii (Psn), isolated from dipladenia (Mandevilla spp.) and
oleander (Nerium oleander), respectively. Therefore, the aim of this work focuses
on the functional characterization of cluster II, not only in bacteria isolated from
woody hosts, but also in strains infecting herbaceous plants.
First, we constructed knockout mutants of most genes encoded in cluster II, i.e.
cheA, cheB, cheD, cheY and two genes coding for chemoreceptors in a woody
plant pathogenic strain, both in Psn23 strain and in P. syringae pv. tomato (Pto)
DC3000. Motility and virulence assays performed in oleander, dipladenia and
tomato plants revealed that cluster II is involved in both phenotypes. In addition,
bioinformatic analysis of the ligand-binding domain (LBD) (1) of the two
chemoreceptors encoded in cluster II showed that only one of them has an LBD
domain. To characterise this chemoreceptor in strain Psn23, capillarity
chemotaxis assays are being performed, and its LBD domain has been purified.
The purified domain will be used in protein-ligand interaction assays against a
collection of plant-derived compounds.
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