Flagella-Driven Motility Is Critical to the Virulence of Xanthomonas fragariae in Strawberry

Abstract

Xanthomonas fragariae (X. fragariae) is the causal agent of angular leaf spots (ALS) in strawberry plants. Recently, a study in China isolated X. fragariae strain YL19, which was observed to cause both typical ALS symptoms and dry cavity rot in strawberry crown tissue, the first X. fragariae strain to have both these effects in strawberry. In this study, from 2020 to 2022, we isolated 39 X. fragariae strains from diseased strawberries in different production areas in China. Multi-locus sequence typing (MLST) and phylogenetic analysis showed that X. fragariae strain YLX21 was genetically different from YL19 and other strains. Tests indicated that YLX21 and YL19 had different pathogenicities towards strawberry leaves and stem crowns. YLX21 did not cause ALS symptoms and rarely caused dry cavity rot in strawberry crown after wound inoculation, and never caused dry cavity rot after spray inoculation, but it did cause severe ALS symptoms after spray inoculation. However, YL19 caused more severe symptoms in strawberry crowns under both conditions. Moreover, YL19 had a single polar flagellum, while YLX21 had no flagellum. Motility and chemotaxis assays showed that YLX21 had weaker motility than YL19, which may explain why YLX21 tended to multiply in situ within the strawberry leaf rather than migrate to other tissues, causing more severe ALS symptoms and mild crown rot symptoms. Taken together, the new strain YLX21 helped us reveal critical factors underlying the pathogenicity of X. fragariae and the mechanism by which dry cavity rot in strawberry crowns forms.

TheXanthomonas fragariaeeffector XopK suppresses stomatal immunity by perturbing abscisic acid accumulation and signaling pathways in strawberry

“…The virulence of the X.fragariae YL19-GFP strain in strawberry plants was determined based on previous studies (Liang et al, 2023; Wang et al, 2023; Wei et al, 2024). The YL19-GFP was cultured in liquid NB medium to OD 600 =1.0 (10 8 cfu/ml), then resuspended in 10 mM MgCl 2 buffer with 0.01% Silwet L-77 for subsequent inoculation assay.…”

An effector XopL enhances ethylene biosynthesis to promoteXanthomonas fragariaeinfection in strawberry

“…Earlier research have given insight into the interaction of strawberry- Xaf using RNA-Seq (Gétaz et al, 2020; Puławska et al, 2020). Most importantly, the genetic information for around 74 Xaf strains was gradually made public (Gétaz et al, 2017; Henry & Leveau, 2016; Vandroemme et al, 2013), including two new strains YL19 and YLX21, which resulted in more severe symptoms in strawberry plants, namely crown dry cavity rot, excluding ALS (Li et al, 2021; Liang et al, 2023). So far, the fact that so little is known about the intricate process of interaction between strawberries and Xaf may be connected to the challenges in overcoming the technical barriers associated with Xaf genetic modification (Vandroemme et al, 2013), as well as the lack of resistant germplasm.…”