The toxic guardians — multiple toxin-antitoxin systems provide stability, avoid deletions and maintain virulence genes of Pseudomonas syringae virulence plasmids

Table 3 Type and proportion of sucrose-resistant derivatives of pPsv48A::Tn5-GDYN1 in the presence or absence of functional toxin-antitoxin systems

	Number (%) of suc^R clones^b
Plasmid size^a	UPN508(pRK415)	UPN508(pRK3A)	ptz ^c	Type of event ^d
- (cured)	2 (0.7)	110 (41.4)	–
57	1 (0.4)	38 (14.3)	+	Recombination^e
70	16 (5.7)	4 (1.5)	+	Reorganizations^f
76	251 (89.0)	111 (41.7)	+	Recombination?^g
89	9 (3.2)	2 (0.8)	+	Spontaneous mutation in sacB
> 90	3 (1.1)	1 (0.4)	+	Reorganizations^h
Total	282	266

^aApproximate size (kb) of the deletion derivative. Total size of pPsv48A::Tn5-GDYN1 is around 89 kb
^bStrain UPN508 contains pPsv48A::Tn5-GDYN1, with functional TA systems. The three TA systems of this plasmid are functionally inactivated in the presence of pRK3A, containing the three cloned antitoxins from pPsv48A
^cPresence (+) or absence (−) of the virulence gene ptz, for cytokinin biosynthesis, in the resulting deletion derivatives
^dAll events resulted in deletion of Tn5-GDYN1, except the spontaneous mutation in sacB
^eRecombination between IS801–1 and IS801–4
^fDiverse group of clones with different, uncharacterized intramolecular reorganizations
^gThe sequence of five clones confirmed that they resulted from recombination between IS801–1 and IS801–2, but we cannot discard the possibility that some or all of the remaining clones resulted from a transposition of IS801–2
^hThese plasmids appeared to result from a transposition of IS801–2, terminating precisely at the end of IS801–1 as determined by sequencing, that eliminate Tn5-GDYN1. According to their relative size on plasmid profile gels, these plasmids must contain an uncharacterized insertion

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