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. 2017 Jan 5;7:40126. doi: 10.1038/srep40126

Figure 4. A conceptual model of Ti-plasmid dynamics in the A. tumefaciens-induced plant tumour.

Figure 4

The model synthesises information from the cited literature and this work to explain the complex dynamics of Ti-plasmids. In step 1, A. tumefaciens pathogens transfer T-DNA into a host plant cell. This costly process may select avirulent A. tumefaciens individuals, altered for T-DNA transfer, because of Ti-plasmid loss or plasmid and chromosomal mutations. In step 2, T-DNA causes tumour development with production of opines that are consumed by A. tumefaciens cells harbouring a Ti-plasmid, leading to their proliferation, in step 3. In step 4, opines induce costly QS-signalling and Ti-plasmid conjugation, which may select QS-altered A. tumefaciens individuals impaired in QS-signal production and Ti-plasmid conjugation, leading to the emergence of potential recipient cells lacking a plasmid or harbouring QS signal-negative plasmid. In step 5, QS-signal induces conjugation, spreading Ti-plasmids to cells lacking them. In this step QS-exploiting cells can spread their QS-altered Ti-plasmid by using extrinsic QS-signal. As we show, QS-degrading lactonases reduce available QS-signal that could potentially be used by QS-altered invaders, thereby limiting their spread to the profit of legitimate QS-cooperators.