Toxin-Antitoxin system HigBA in Xylella fastidiosa is expressed at low temperature but does not impact virulence or grapevine recovery in greenhouse trials

Authors: Wei, Wei; Burbank, Lindsey

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2022
Publication Date: 10/12/2022
Citation: Wei, W., Burbank, L.P. 2022. Toxin-Antitoxin system HigBA in Xylella fastidiosa is expressed at low temperature but does not impact virulence or grapevine recovery in greenhouse trials. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-02-22-0009-R.
DOI: https://doi.org/10.1094/PHYTOFR-02-22-0009-R

Interpretive Summary: Bacterial pathogen of grapevines Xylella fastidiosa has multiple genes known as toxin-antitoxin systems because the antitoxin prevents toxic activity of the toxin. Two of these genes called higA and higB are investigated in this study to determine what their role is during bacterial infection in plants. At a lower temperature, more of the toxin (higB) and the antitoxin (higA) are produced compared with when the bacteria are grown at a higher temperature. This is important to understanding how Xylella fastidiosa grows in different environmental conditions. However, higA and higB do not seem to be important for bacterial survival at low temperature or for infection of grapevines.

Technical Abstract: Xylella fastidiosa has multiple chromosomally encoded type II toxin-antitoxin (TA) systems, several of which have unknown functions in the bacterial lifecycle. In many bacterial species, type II TA systems are associated with bacterial stress survival under various detrimental environmental conditions, as well as influencing disease associated phenotypes such as biofilm development and expression of virulence factors. Chromosomal TA systems are often found in genomic regions with evidence of phage insertion, pointing to potential acquisition of these elements by horizontal gene transfer. One of the TA systems found in X. fastidiosa, higBA is transcriptionally expressed at higher levels at 15°C than at 28°C. However, a higBA deletion mutant ('higBA) in X. fastidiosa subsp. fastidiosa Stag’s Leap is not deficient in growth or viability under in vitro cold stress and is able to infect grapevines causing disease comparable to the wild type strain. Grapevines infected with X. fastidiosa 'higBA recover from infection following cold treatment at 4°C at a rate similar to wild type infected plants, suggesting this TA system does not contribute significantly to X. fastidiosa survival at low temperature in planta. Although still unable to provide a definitive function for HigBA in X. fastidiosa, this study adds to a growing body of work describing functions and expression dynamics of TA systems in plant pathogenic bacteria.