Identification and characterization of ISXax2, a TN3-like transposable element potentially related with the virulence and pathogenicity of Xanthomonas citri subsp. citri

• Autor(a) principal: Ferreira, Rafael Marini [UNESP]
• Data de Publicação: 2014
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UNESP
• Texto Completo: http://hdl.handle.net/11449/121984
• topic: Cítricos - Doenças e pragas; Cancro citrico; Bacterias fitopatogenicas; Xanthomonas; Genômica; Proteínas; Genetica vegetal; Genomics

Citrus canker (CC) is an important disease affecting many citrus species. It can result from infection by Xanthomonas citri subsp. citri (Xac) and can be transmitted by water, contact or propagation of infected leaves. Comparative studies have shown that one of the most intriguing features within the Xanthomonas genus is the extraordinary genome plasticity and highly mosaic architecture. This is largely the consequence of genomic rearrangements involving several genomic islands (GI), insertion sequences (IS), and few prophages insertion events. High quality IS annotation coupled with comparative genomics revealed a complete transposon of the Tn3 family in the Xanthomonas citri genome (ISXax2), with several T3SEs passenger genes, including a highly conserved lytic murein transglycosylase (mlt), a helper protein of the T3SS. Random transposon insertion was used to generate XacΔmltB and site directed mutagenesis was used to generate the XacΔmlt mutant. Using ISXax2 from Xac as an example we demonstrated that the plasmid copy of mltB (mlt) was indeed functional and required to generate symptoms in vivo. Transposition assays showed transposition rates for ISXax2 with a frequency of about 1.65 x 10-5. In this study we have used a mixture of bioinformatic and experimental approaches to address the role and behavior of such potentially transposable element. We showed that the entire structure was capable of transposition and that MICs (Mobile Insertion Cassettes) containing TAL effectors could also be mobilized. These results provide strong evidence that, in the case of Xac and closely related species, pathogenicity and virulence genes can be spread by a Tn3-like transposition mechanism, using conjugative plasmids as intercellular vectors. We propose that this process is a key agent to modulate the bacterial virulence and the host-specificity in this group of plant pathogens