Role of phenolic compounds in imparting tolerance to Xylella fastidiosa in Pierce’s disease susceptible and resistant grapevines

Authors: Wallis, Christopher; ZEILINGER, ADAM - University Of California; SICARD, ANNE - University Of California; BEAL, DYLAN - University Of California; WALKER, ANDREW - University Of California; ALMEIDA, RODRIGO - University Of California

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2020
Publication Date: 8/7/2020
Citation: Wallis, C.M., Zeilinger, A.R., Sicard, A., Beal, D., Walker, A., Almeida, R.P. 2020. Role of phenolic compounds in imparting tolerance to Xylella fastidiosa in Pierce’s disease susceptible and resistant grapevines. PLoS One. 15(8):e0237545. https://doi.org/10.1371/journal.pone.0237545.
DOI: https://doi.org/10.1371/journal.pone.0237545

Interpretive Summary: Pierce’s disease is of major concern to grapevine production wherever both the bacterial pathogen Xylella fastidiosa and sharpshooter vectors are present. To combat Pierce’s disease, a resistant grapevine, containing the PdR1 locus, has been bred by crossing domesticated and wild grapevine species. However, mechanisms of resistance remain unknown. Therefore, it was hypothesized that differences in phenolic compounds produced in response to Xylella fastidiosa infection may provide observed tolerance that prevents PdR1 containing grapevines from developing Pierce’s disease. Phenolic levels overall were lower in PdR1-containing grapevines compared to those without PdR1. The reduction in phenolic levels, specifically flavonoids, may affect biofilm formation and bacterial movement therefore altering Xylella fastidiosa virulence. A similar trait can be targeted in future breeding programs to combat diseases caused by Xylella fastidiosa or similar bacterial pathogens.

Technical Abstract: Pierce’s disease is of major concern for grapevine (Vitis vinifera) production wherever the bacterial pathogen Xylella fastidiosa and its sharpshooter vectors are present. Long term management includes deployment of resistant grapevines such as those containing the PdR1 locus from wild grapevine species Vitis arizonica, which does not develop Pierce’s disease upon infection. However, little is understood about how the PdR1 locus functions to prevent disease symptom development. To this end, it was hypothesized that plant defense-associated compounds called phenolics may vary in levels between PdR1-containing and PdR1-absent grapevine siblings, as PdR1 could be involved in modulating defense responses. Soluble foliar phenolic levels, especially flavonoids, in Xylella-infected PdR1-resistant grapevines were discovered to be significantly lower than those in infected susceptible grapevines. It is therefore hypothesized that PdR1-resistant grapevines, by possessing lowered flavonoid levels, affected biofilm formation and cause reduced Xylella fastidiosa intra-plant colonization thus limiting the ability to increase populations and cause Pierce’s disease. These results therefore reveal that differences in plant metabolite levels might be a component of the mechanisms that PdR1 utilizes to prevent Pierce’s disease.