Genomic Insights into the Evolutionary Origin of Xanthomonas axonopodis pv. citri and Its Ecological Relatives

Abstract

Xanthomonas axonopodis pv. citri (Xac) is the causal agent of citrus bacterial canker (CBC) and is a serious problem worldwide. Like CBC, several important diseases in other fruits, such as mango, pomegranate, and grape, are also caused by Xanthomonas pathovars that display remarkable specificity toward their hosts. While citrus and mango diseases were documented more than 100 years ago, the pomegranate and grape diseases have been known only since the 1950s and 1970s, respectively. Interestingly, diseases caused by all these pathovars were noted first in India. Our genome-based phylogenetic studies suggest that these diverse pathogens belong to a single species and these pathovars may be just a group of rapidly evolving strains. Furthermore, the recently reported pathovars, such as those infecting grape and pomegranate, form independent clonal lineages, while the citrus and mango pathovars that have been known for a long time form one clonal lineage. Such an understanding of their phylogenomic relationship has further allowed us to understand major and unique variations in the lineages that give rise to these pathovars. Whole-genome sequencing studies including ecological relatives from their putative country of origin has allowed us to understand the evolutionary history of Xac and other pathovars that infect fruits.

Ecological and Evolutionary Insights into Xanthomonas citri Pathovar Diversity

“…centellae LMG 9044. This region was found to correspond to nonribosomal peptide synthetases and polyketide synthases (NRPS-PKS) as previously reported (49). Second, among the XCPs, a region (D1) was found to be exclusively present in X. campestris pv.…”

“…For instance, the presence of a unique NRPS-PKS cluster in X. campestris pv. mangiferaeindicae LMG 941 is possibly involved in the production of a novel metabolite (49).…”

“…From the present study, we report the genomes of 18 reference pathovar strains of XCPs and compare them with those of 4 publicly available XCPs (46)(47)(48)(49). However, these XCPs have historically been classified into three different species of Xanthomonas and one of these strains has been assigned to another genus, Pseudomonas ( Table 1).…”

Xanthomonas citri pv. citri Pathotypes: LPS Structure and Function as Microbe‐Associated Molecular Patterns

“…The vast majority of commercial citrus cultivars can be infected by X. citri pv. citri , although with variation in host susceptibility . Evolutionary analysis allowed the recognition of X. citri pv.…”

“…Pathotype A infects almost all citrus species and is widespread throughout the world, whereas pathotypes A* and A W are associated with natural outbreaks only in Mexican lime ( C. aurantifolia ) and its close relative C . macrophylla . Despite progress in the comprehension of the X. citri pv.…”