Identification of an Operon, Pil-Chp, That Controls Twitching Motility and Virulence in Xylella fastidiosa

Abstract

Xylella fastidiosa is an important phytopathogenic bacterium that causes many serious plant diseases, including Pierce's disease of grapevines. Disease manifestation by X. fastidiosa is associated with the expression of several factors, including the type IV pili that are required for twitching motility. We provide evidence that an operon, named Pil-Chp, with genes homologous to those found in chemotaxis systems, regulates twitching motility. Transposon insertion into the pilL gene of the operon resulted in loss of twitching motility (pilL is homologous to cheA genes encoding kinases). The X. fastidiosa mutant maintained the type IV pili, indicating that the disrupted pilL or downstream operon genes are involved in pili function, and not biogenesis. The mutated X. fastidiosa produced less biofilm than wild-type cells, indicating that the operon contributes to biofilm formation. Finally, in planta the mutant produced delayed and less severe disease, indicating that the Pil-Chp operon contributes to the virulence of X. fastidiosa, presumably through its role in twitching motility.

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…Further evidence of the need for complex regulation of type IV pili function in X. fastidiosa is the observation that a chemosensory system is operative. An operon named Pil-Chp containing genes homologous to those found in chemotaxis systems of other bacteria were found to be required for proper pilus function but not biogenesis in X. fastidiosa (Cursino et al 2011). Such regulatory mutants were also deficient in colonization of plants, suggesting that complex regulation of pilus function may also occur in plants (Cursino et al 2011).…”

“…An operon named Pil-Chp containing genes homologous to those found in chemotaxis systems of other bacteria were found to be required for proper pilus function but not biogenesis in X. fastidiosa (Cursino et al 2011). Such regulatory mutants were also deficient in colonization of plants, suggesting that complex regulation of pilus function may also occur in plants (Cursino et al 2011). While such regulators are apparently required for motility, it remains unclear whether X. fastidiosa exhibits chemotactic movement toward or away from particular compounds.…”

Calcium-Enhanced Twitching Motility in Xylella fastidiosa Is Linked to a Single PilY1 Homolog

“…Mutation of the type IV pilus genes pilQ, pilB, fimT, pilX, and pilO prevented TFP production and motility in vitro (5,25), and mutation of one pilY1 homolog (PD0023) caused diminished motility (25,26). Additionally, different regulatory systems have been implicated in twitching modulation, such as the quorum-sensing signaling molecule diffusible signal factor (DSF), which represses motility (27); pilR-pilS, a two-component regulatory system that activates pilA transcription (25); and the chemosensory Pil-Chp operon, which regulates TFP production and response (28). Furthermore, dis-ruption of genes implicated in the production or function of TFP in X. fastidiosa resulted in delayed and less-severe symptoms in planta (28).…”

The chemotaxis regulator pilG of Xylella fastidiosa is required for virulence in Vitis vinifera grapevines

“…The transcription of pilA was regulated by pilR, a response regulator in a twocomponent sensor-regulator pair pilS/pilR system (Winther-Larsen and Koomey 2002). The activity of twitching motility of X. fastidiosa was controlled by a chemotaxis-like regulatory system (Cursino et al 2011), Pil-Chp operon, similar to that in P. aeruginosa and E. coli (Ferandez et al 2002;Fulcher et al 2010;Hazelbauer et al 2008;Kirby 2009). Like P. aeruginosa CheIV (Pil-Chp) cluster (Ferandez et al 2002;Fulcher et al 2010), X. fastidiosa possesses a single predicated chemosensory system, Pil-Chp operon that regulates the twitching motility of type IV pili (Fulcher et al 2010;Simpson et al 2000).…”

“…Like P. aeruginosa CheIV (Pil-Chp) cluster (Ferandez et al 2002;Fulcher et al 2010), X. fastidiosa possesses a single predicated chemosensory system, Pil-Chp operon that regulates the twitching motility of type IV pili (Fulcher et al 2010;Simpson et al 2000). Pil-Chp operon of X. fastidiosa encodes proteins involved in signal transduction pathways including pilG, pilI, pilJ, pilL, chpB and chpC as in P. aeruginosa and E. coli (Cursino et al 2011;Fulcher et al 2010;Kirby 2009). Upon binding of the chemical stimuli in the periplasmic domain, the transmembrane chemoreceptors activate a signaling cascade in the cytoplasmic portion and ultimately control bacterial twitching motility (Cursino et al 2011).…”