A Genomic Locus Unique to Blueberry-Infecting Xylella fastidiosa Strains Affects Motility and Bi

03 Apr 20264 min read0 viewsJournal Feed

GIST

by Navdeep Kaur, Marcus V. Merfa, Alexandra K.

Kahn, Rodrigo P. P.

Almeida, Leonardo De La Fuente Xylella fastidiosa ( Xf ) is an insect-transmitted, xylem-limited bacterial plant pathogen that infects hundreds of plant species. This pathogen causes bacterial leaf scorch in southern highbush blueberry ( Vaccinium corymbosum interspecific hybrids) in the southeastern United States, a disease that has not yet been reported elsewhere.

Previously, a comparative genomic analysis of Xf and ancestral host species identified evolutionary events of gene gain and loss related to host range specificity. Here, by using a similar workflow, we identified two loci that are significantly found in blueberry-infecting strains.

Locus_1088 included a hypothetical protein and a small part of the N-terminus of an orphan RelE toxin, while Locus_2741 was annotated as a hypothetical protein. Using a protocol based on natural competence, mutants were generated in three Xf subsp.

multiplex strains from blueberry. Less biofilm, more planktonic growth, and increased twitching motility as compared to its wild-type (WT) were observed for the strain LA-Y3C_1088 mutant.

Clinical Editorial

Genomic signals associated with blueberry infection

Locus_1088 contains a hypothetical protein and a partial N-terminus fragment of an orphan RelE toxin; Locus_2741 encodes another hypothetical protein.

The researchers used a comparative genomics approach to highlight these loci based on their association with blueberry-infecting strains.

The study identifies two genomic loci uniquely enriched in Xylella fastidiosa strains that infect blueberry.

Functional impact in vitro

multiplex blueberry strains using a natural-competence-based protocol.

Mutants were generated in three Xf subsp.
In vitro, the LA-Y3C_1088 mutant showed a shift toward less biofilm formation, increased planktonic growth, and greater twitching motility compared with its wild-type counterpart.
The LA-Y3C_1088 mutant also disrupted a toxin component of a toxin–antitoxin system, which is proposed to contribute to the observed phenotypes.
For the other mutated strains, no consistent differences from wild-type were reported in the abstract.

In planta virulence context

When tested in blueberry, CFBP8073 induced severe symptoms comparable to a known blueberry control strain ( AlmaEm3).

In blueberry virulence assays, the LA-Y3C_1088 mutant produced significantly more severe symptoms than the LA-Y3C_WT control, indicating enhanced virulence for this specific locus disruption.
No significant virulence differences were observed for the other mutated strains in blueberry assays.
An additional strain, CFBP8073 (coffee-isolated, not previously tested in blueberry) was found to encode the same two blueberry-associated loci.

Interpretation and limitations

However, because two independent mutants for locus 1088 were not generated, the study cannot definitively attribute the phenotype to disruption of the hypothetical protein versus the toxin fragment.

The findings suggest a possible link between locus 1088 and altered motility, biofilm formation, and virulence in blueberry-infected Xf, potentially involving disruption of a toxin component within a toxin–antitoxin system.
The presence of the same loci in a coffee-associated strain (CFBP8073) that elicited blueberry-like virulence highlights the complexity of host specificity in Xf and indicates these loci alone may not fully determine host range.

Context and significance

The work emphasizes that identifying genetic markers linked to host specificity in Xf could improve disease management by informing surveillance and control strategies across hosts and regions.
The researchers underscore the need for further functional validation to disentangle the roles of the hypothetical proteins versus toxin-related components in shaping phenotype and host interactions.