Comparative genomic characterization of citrus-associated Xylella fastidiosa strains

Abstract

Background: The xylem-inhabiting bacterium Xylella fastidiosa (Xf) is the causal agent of Pierce's disease (PD) in vineyards and citrus variegated chlorosis (CVC) in orange trees. Both of these economically-devastating diseases are caused by distinct strains of this complex group of microorganisms, which has motivated researchers to conduct extensive genomic sequencing projects with Xf strains. This sequence information, along with other molecular tools, have been used to estimate the evolutionary history of the group and provide clues to understand the capacity of Xf to infect different hosts, causing a variety of symptoms. Nonetheless, although significant amounts of information have been generated from Xf strains, a large proportion of these efforts has concentrated on the study of North American strains, limiting our understanding about the genomic composition of South American strains -which is particularly important for CVC-associated strains.

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…Only one study addressed this question at the subspecies level (subsp. pauca); it showed that the pan-genome of X. fastidiosa is potentially large and that differences among isolates were associated with genome island-like fragments (da Silva et al 2007). However, representative genomes of different subspecies that have been fully sequenced are largely syntenic ( Fig.…”

Comparative genomic analysis of coffee-infecting Xylella fastidiosa strains isolated from Brazil

“…All X. fastidiosa strains used in this work (Table 1) Primary isolation of the strains was performed as described previously (da Silva et al, 2007). Briefly, symptomatic leaves from infected plants were collected, washed and disinfected; the petioles were placed in a plastic tube with PBS and ground in a tissue grinder.…”

“…For this work, the bacteria were recovered on PW agar medium and the plates maintained for 10 days at 28 uC. The colonies were transferred once to new plates containing the same medium, grown for 20 days and harvested for DNA extraction, as described previously (da Silva et al, 2007).…”

“…More importantly, comparative studies have shown that a surprisingly large proportion of genes present in the flexible gene pool of X. fastidiosa are shared amongst distantly related strains, indicating the possibility that the bacteria are actively and constantly exchanging genetic material in the wild da Silva et al, 2007) -a possibility that is reinforced by the recent demonstration that X. fastidiosa cells display natural competence for transformation via uptake of exogenous DNA (Kung & Almeida, 2011;Kung et al, 2013). Comparative analyses also suggest that X. fastidiosa genomes might evolve at a very fast pace, taking advantage of such a large number of HTEs and the fact that different strains are constantly coming into contact with one another through mixed infections that occur in the same host (particularly in insects) (Chen et al, 2005;Costa et al, 2006).…”

“…So far, there is only one work that attempted to perform a genomic survey of South American X. fastidiosa strains (da Silva et al, 2007) and this study did not involve whole-genomic sequencing, but microarraybased comparisons, followed by suppressive subtractive hybridization. Moreover, these analyses focused only on citrus-infecting X. fastidiosa strains, overlooking the contribution of coffee-related strains to the evolutionary history of the South American X. fastidiosa group.…”