A TALE of transposition : Tn3-like transposons play a major role in the spread of pathogenicity determinants of Xanthomonas citri and other Xanthomonads.
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2015
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Abstract
Members of the genus Xanthomonas are among the most important phytopathogens. A key feature of Xanthomonas
pathogenesis is the translocation of type III secretion system (T3SS) effector proteins (T3SEs) into the plant target cells via a
T3SS. Several T3SEs and a murein lytic transglycosylase gene (mlt, required for citrus canker symptoms) are found associated
with three transposition-related genes in Xanthomonas citri plasmid pXAC64. These are flanked by short inverted repeats (IRs).
The region was identified as a transposon, TnXax1, with typical Tn3 family features, including a transposase and two recombination
genes. Two 14-bp palindromic sequences within a 193-bp potential resolution site occur between the recombination genes.
Additional derivatives carrying different T3SEs and other passenger genes occur in different Xanthomonas species. The T3SEs
include transcription activator-like effectors (TALEs). Certain TALEs are flanked by the same IRs as found in TnXax1 to form
mobile insertion cassettes (MICs), suggesting that they may be transmitted horizontally. A significant number of MICs carrying
other passenger genes (including a number of TALE genes) were also identified, flanked by the same TnXax1 IRs and delimited
by 5-bp target site duplications. We conclude that a large fraction of T3SEs, including individual TALEs and potential pathogenicity
determinants, have spread by transposition and that TnXax1, which exhibits all of the essential characteristics of a functional
transposon, may be involved in driving MIC transposition. We also propose that TALE genes may diversify by fork slippage
during the replicative Tn3 family transposition. These mechanisms may play a crucial role in the emergence of
Xanthomonas pathogenicity.
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FERREIRA, R. M. et al. A TALE of transposition: Tn3-like transposons play a major role in the spread of pathogenicity determinants of Xanthomonas citri and other Xanthomonads. mBio, v. 6, p. e02505-14, 2015. Disponível em: <http://mbio.asm.org/content/6/1/e02505-14.full.pdf+html>. Acesso em: 05 ago. 2017.