Abstract
Citrus canker is a major disease affecting citrus production in Brazil. It’s mainly caused by Xanthomonas citri subsp. citri strain 306 pathotype A (Xac). We analysed the differential expression of proteins secreted by wild type Xac and an asymptomatic mutant for hrpB4 (ΔhrpB4) grown in Nutrient Broth (NB) and a medium mimicking growth conditions in the plant (XAM1). This allowed the identification of 55 secreted proteins, of which 37 were secreted by both strains when cultured in XAM1. In this secreted protein repertoire, the following stand out: Virk, Polyphosphate-selective porin, Cellulase, Endoglucanase, Histone-like protein, Ribosomal proteins, five hypothetical proteins expressed only in the wild type strain, Lytic murein transglycosylase, Lipoprotein, Leucyl-tRNA synthetase, Co-chaperonin, Toluene tolerance, C-type cytochrome biogenesis membrane protein, Aminopeptidase and two hypothetical proteins expressed only in the ΔhrpB4 mutant. Furthermore, Peptidoglycan-associated outer membrane protein, Regulator of pathogenicity factor, Outer membrane proteins, Endopolygalacturonase, Chorismate mutase, Peptidyl-prolyl cis-trans isomerase and seven hypothetical proteins were detected in both strains, suggesting that there was no relationship with the secretion mediated by the type III secretory system, which is not functional in the mutant strain. Also worth mentioning is the Elongation factor Tu (EF-Tu), expressed only the wild type strain, and Type IV pilus assembly protein, Flagellin (FliC) and Flagellar hook-associated protein, identified in the wild-type strain secretome when grown only in NB. Noteworthy, that FliC, EF-Tu are classically characterized as PAMPs (Pathogen-associated molecular patterns), responsible for a PAMP-triggered immunity response. Therefore, our results highlight proteins potentially involved with the virulence. Overall, we conclude that the use of secretome data is a valuable approach that may bring more knowledge of the biology of this important plant pathogen, which ultimately can lead to the establishment of new strategies to combat citrus canker.
Highlights
Proteins secreted by bacteria are known to have key functions, such as the provision of nutrients, cell–cell communication, detoxification, inhibition of potential competitors, etc. (Tseng, Tyler & Setubal, 2009)
Considering that the XAM1 medium simulates conditions experienced by Xanthomonas citri subsp. citri (Xac) during plant infections or when Xac is in contact with the plant meristem, the former set of proteins are considered the repertoire of proteins required for pathogenicity and adaptation during infections
Our results indicate that the secretome analysis is a valuable approach to highlight proteins potentially involved with the virulence in Xanthomonas
Summary
Proteins secreted by bacteria are known to have key functions, such as the provision of nutrients, cell–cell communication, detoxification, inhibition of potential competitors, etc. (Tseng, Tyler & Setubal, 2009). (Tseng, Tyler & Setubal, 2009). The extracellular proteins of pathogenic bacteria play a critical role in their pathogenicity and adaptation to a compatible host (Kamoun et al, 1993; Qian et al, 2013). Six types of secretory systems (SS), which have been previously described, are critical for exporting proteins to the external environment or for directly contacting the host (Tseng, Tyler & Setubal, 2009). Secreted proteins (secretomes) from different organisms cultivated in different physiological conditions have been analysed, which often validates biological information derived from genomic sequencing projects. Previous studies have focused on the secretomes of specialized secretion apparatuses, which include the Tat (Pickering, Yudistira & Oresnik, 2012), T3SS (Deng et al, 2010) and T2SS secretomes (Sikora et al, 2011). Comparative proteomics, which aims to compare the secretomes of different bacterial strains cultivated in the same physiological conditions (Xu et al, 2013) or the secretomes of the same strain cultivated in different physiological conditions or hosts (Villeth et al, 2009), has gained traction
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
