Natural Genetic Variation of Xanthomonas campestris pv. campestris Pathogenicity onArabidopsisRevealed by Association and Reverse Genetics

Abstract

The pathogenic bacterium Xanthomonas campestris pv. campestris, the causal agent of black rot of Brassicaceae, manipulates the physiology and the innate immunity of its hosts. Association genetic and reverse-genetic analyses of a world panel of 45 X. campestris pv. campestris strains were used to gain understanding of the genetic basis of the bacterium’s pathogenicity to Arabidopsis thaliana. We found that the compositions of the minimal predicted type III secretome varied extensively, with 18 to 28 proteins per strain. There were clear differences in aggressiveness of those X. campestris pv. campestris strains on two Arabidopsis natural accessions. We identified 3 effector genes (xopAC, xopJ5, and xopAL2) and 67 amplified fragment length polymorphism (AFLP) markers that were associated with variations in disease symptoms. The nature and distribution of the AFLP markers remain to be determined, but we observed a low linkage disequilibrium level between predicted effectors and other significant markers, suggesting that additional genetic factors make a meaningful contribution to pathogenicity. Mutagenesis of type III effectors in X. campestris pv. campestris confirmed that xopAC functions as both a virulence and an avirulence gene in Arabidopsis and that xopAM functions as a second avirulence gene on plants of the Col-0 ecotype. However, we did not detect the effect of any other effector in the X. campestris pv. campestris 8004 strain, likely due to other genetic background effects. These results highlight the complex genetic basis of pathogenicity at the pathovar level and encourage us to challenge the agronomical relevance of some virulence determinants identified solely in model strains.

xopAC-triggered Immunity against Xanthomonas Depends on Arabidopsis Receptor-Like Cytoplasmic Kinase Genes PBL2 and RIPK

“…xopAC confers avirulence to Xcc only when bacteria are inoculated into the vascular system of the Columbia-0 (Col-0) ecotype of A. thaliana by piercing the main leaf vein, but not by mesophyll infiltration [27–29]. xopAC encodes a protein with an N-terminal LRR domain and a C-terminal fic (filamentation-induced by cAMP, consensus HPFxxG/ANGR) domain [28].…”

Testing of Inoculation Methods and Susceptibility Testing of Perspective Cabbage Breeding Lines (Brassica Oleracea convar. Capitata) to the Black Rot Disease Caused by Xanthomonas Campestris pv. Campestris

“…Comparing the reactions of plants to individual isolates and mixture, they stated no indications of an interaction between races in inoculum. The isolate 3811 is the reference strain for Xcc race 1 and is often used in studies of Xcc identification, pathogenicity or diversity (Guy et al, 2013;Jensen et al, 2010;Vicente et al 2001). The isolate 1279A represents the reference strain for Xcc race 4 and is also used in scientific researches (Bila et al, 2013;Chitarra et al, 2002;Taylor et al, 2002).…”

Genome Sequences of Three Atypical Xanthomonas campestris pv. campestris Strains, CN14, CN15, and CN16

“…Seven genomic clades (A to G) of X. campestris pv. campestris have been defined (2). As yet, genomic resources are available for only clades A and C (3–6).…”

“…Interestingly, clade G strains seem to represent ancestral X. campestris pv. campestris strains that have not been described so far (2). …”