Xanthomonas citri subsp. citri and Xanthomonas arboricola pv. pruni: Comparative analysis of two pathogens producing similar symptoms in different host plants.

Jerson Garita-Cambronero,Jaime Cubero,Elisa Ferragud,Marta Sena-Vélez,Cristina Redondo,Pilar Sabuquillo

doi:10.1371/journal.pone.0219797

Abstract

Comparative studies in Xanthomonas have provided a vast amount of data that enabled to deepen in the knowledge of those factors associated with virulence and Xanthomonas plant interaction. The species of this genus present a wide range of host plants and a large number of studies have been focused to elucidate which mechanism are involved in this characteristic. In this study, comparative genomic and phenotypic analysis were performed between X. citri subsp. citri (Xcc), one of the most studied pathogens within Xanthomonas, and X. arboricola pv. pruni (Xap), a pathogen which has aroused great interest in recent time. The work was aimed to find those elements that contribute to their host divergence despite the convergence in the symptoms that each species cause on Citrus spp. and Prunus spp., respectively. This study reveals a set of genes that could be putatively associated with the adaptation of these pathogens to their hosts, being the most remarkable those involved in environmental sensing systems such as the case of the TonB-dependent transporters, the sensors of the two-component system and the methyl accepting chemotaxis proteins. Other important variants were found in processes related to the decomposition of the cell wall as could be appreciated by their dissimilar set of cell-wall degrading enzymes. Type three effectors, as one of the most important factors in delineating the host specificity in Xanthomonas, also showed a different array when comparing both species, being some of them unique to each pathogen. On the other hand, only small variations could be connected to other features such as the motility appendages and surface adhesion proteins, but these differences were accompanied by a dissimilar capacity to attach on host and non-host leaf surface. The molecular factors found in this work provide the basis to perform a more in-depth functional analyses that unveil those actual factors associated with pathogenesis and host specificity in Xcc and Xap.

Highlights

Xanthomonas is a large genus of bacteria that encompasses species associated with plants causing serious economic losses in significant crops
Xanthomonas citri subsp citri (Xcc) and Xanthomonas arboricola pv. pruni (Xap) are spread by wind-blown rains and may enter to the plant by injures or through the stomata, multiplying inside the tissue and being disseminated when proper humidity and temperature condition are present in the environment
This work was aimed to improve the knowledge of the possible mechanisms involved in the infection of two Xanthomonas species and to determine those that may play a key role in host range

Summary

Introduction

Xanthomonas is a large genus of bacteria that encompasses species associated with plants causing serious economic losses in significant crops. Among the plant diseases due to xanthomonads, two are considered specially relevant in fruit trees, Xanthomonas citri subsp citri (Xcc), the causal agent of citrus bacterial canker (CBC) and Xanthomonas arboricola pv. CBC is considered one of the major threat for citriculture and it is endemic in many citrus production zones, even though, Xcc is not present in other areas such as the Mediterranean basin or California in USA, where these bacteria are regulated as quarantinable [4]. BSF is worldwide distributed with a presence in most Prunus-growing regions, Xap is still a quarantine organism in some areas like the European Union [5,6]. CBC is defined as a tropical or subtropical disease; BSF occurs mostly in temperate areas. Xcc and Xap, cause lesions in leaf, fruit, stems and branches that visually may like quite similar between the two [2,3]

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