Characterization of Regulatory Pathways in Xylella fastidiosa : Genes and Phenotypes Controlled by gacA

Abstract

The xylem-limited, insect-transmitted bacterium Xylella fastidiosa causes Pierce's disease in grapes through cell aggregation and vascular clogging. GacA controls various physiological processes and pathogenicity factors in many gram-negative bacteria, including biofilm formation in Pseudomonas syringae pv. tomato DC3000. Cloned gacA of X. fastidiosa was found to restore the hypersensitive response and pathogenicity in gacA mutants of P. syringae pv. tomato DC3000 and Erwinia amylovora. A gacA mutant of X. fastidiosa (DAC1984) had significantly reduced abilities to adhere to a glass surface, form biofilm, and incite disease symptoms on grapevines, compared with the parent (A05). cDNA microarray analysis identified 7 genes that were positively regulated by GacA, including xadA and hsf, predicted to encode outer membrane adhesion proteins, and 20 negatively regulated genes, including gumC and an antibacterial polypeptide toxin gene, cvaC. These results suggest that GacA of X. fastidiosa regulates many factors, which contribute to attachment and biofilm formation, as well as some physiological processes that may enhance the adaptation and tolerance of X. fastidiosa to environmental stresses and the competition within the host xylem.

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…While any signal that this response regulator might perceive remains unknown, it is intriguing to consider that it might be involved in habitat-specific expression of those genes such as hxfA, hxfB, and tonB which, as discussed above, play central roles in the behavior of X. fastidiosa in different settings. The global regulator GacA was also found to positively regulate several virulence factors in X. fastidiosa including the adhesins XadA and Hsf (Shi et al 2009). GacA has been found to control a variety of physiological processes as well as pathogenicity factors in many other gram-negative bacteria (Heeb and Haas 2001).…”

Expression of Xylella fastidiosa Fimbrial and Afimbrial Proteins during Biofilm Formation

“…Translation could be affected by small regulatory RNAs mediated by gacA. Activity of small RNAs related to gacA has been demonstrated for Pseudomonas aeruginosa and also for X. fastidiosa (26,47,52). In the latter case, regulation via gacA directly affects xadA1 and xadA2 expression and thus cell-cell adhesion and biofilm formation (52).…”

Phenotype Overlap in Xylella fastidiosa Is Controlled by the Cyclic Di-GMP Phosphodiesterase Eal in Response to Antibiotic Exposure and Diffusible Signal Factor-Mediated Cell-Cell Signaling

“…The attachment to surfaces and thus biofilm formation is a major life strategy required for dissemination of X. fastidiosa by insects (54,55). Once inside xylem vessels of host plants, X. fastidiosa proliferates and spreads, apparently mostly as planktonic cells, although some can attach to the plant.…”