Abstract
Nicotiana otophora contains Agrobacterium-derived T-DNA sequences introduced by horizontal gene transfer (Chen etal., 2014). Sixty-nine contigs were assembled into four different cellular T-DNAs (cT-DNAs) totalling 83kb. TC and TE result from two successive transformation events, each followed by duplication, yielding two TC and two TE inserts. TC is also found in other Nicotiana species, whereas TE is unique to N. otophora. Both cT-DNA regions are partially duplicated inverted repeats. Analysis of the cT-DNA divergence patterns allowed reconstruction of the evolution of the TC and TE regions. TC and TE carry 10 intact open reading frames. Three of these are TE-6b genes, derived from a single 6b gene carried by the Agrobacterium strain which inserted TE in the N. otophora ancestor. 6b genes have so far only been found in Agrobacterium tumefaciens or Agrobacterium vitis T-DNAs and strongly modify plant growth (Chen and Otten, 2016). The TE-6b genes were expressed in Nicotiana tabacum under the constitutive 2×35S promoter. TE-1-6b-R and TE-2-6b led to shorter plants, dark-green leaves, a strong increase in leaf vein development and modified petiole wings. TE-1-6b-L expression led to a similar phenotype, but in addition leaves show outgrowths at the margins, flowers were modified and plants became viviparous, i.e. embryos germinated in the capsules at an early stage of their development. Embryos could be rescued by culture invitro. The TE-6b phenotypes are very different from the earlier described 6b phenotypes and could provide new insight into the mode of action of the 6b genes.
Highlights
Several plant species carry Agrobacterium T-DNA sequences in their genomes and can be considered as ‘natural transformants’. cellular T-DNAs (cT-DNAs) were most likely introduced by infection with Agrobacterium rhizogenes and subsequent regeneration of hairy roots (Matveeva and Lutova, 2014; Chen and Otten, 2017). cT-DNAs have been found in Nicotiana (White et al, 1983; Furner et al, 1986; Chen et al, 2014), Linaria vulgaris (Matveeva et al, 2012) and Ipomoea batatas (Kyndt et al, 2015)
Expression of the Nicotiana glauca genes Ngorf13 and NgrolC and of the Nicotiana tabacum genes torf13 and trolC in various test plants demonstrated that they have growth-modifying properties similar to their A. rhizogenes equivalents (Meyer et al, 1995; Fru€ndt et al, 1998a,b; Aoki and Syono, 1999b,c, 2000; Aoki, 2004; Mohajjel-Shoja, 2010; Mohajjel-Shoja et al, 2011)
Since N. otophora TW95 was used to obtain genomic and transcriptome sequence data (Sierro et al, 2014), we used this accession for our studies
Summary
Several plant species carry Agrobacterium T-DNA sequences (cellular T-DNAs or cT-DNAs) in their genomes and can be considered as ‘natural transformants’. cT-DNAs were most likely introduced by infection with Agrobacterium rhizogenes and subsequent regeneration of hairy roots (Matveeva and Lutova, 2014; Chen and Otten, 2017). cT-DNAs have been found in Nicotiana (White et al, 1983; Furner et al, 1986; Chen et al, 2014), Linaria vulgaris (Matveeva et al, 2012) and Ipomoea batatas (Kyndt et al, 2015).Expression of the Nicotiana glauca genes Ngorf and NgrolC and of the Nicotiana tabacum genes torf and trolC in various test plants demonstrated that they have growth-modifying properties similar to their A. rhizogenes equivalents (Meyer et al, 1995; Fru€ndt et al, 1998a,b; Aoki and Syono, 1999b,c, 2000; Aoki, 2004; Mohajjel-Shoja, 2010; Mohajjel-Shoja et al, 2011). CT-DNAs were most likely introduced by infection with Agrobacterium rhizogenes and subsequent regeneration of hairy roots (Matveeva and Lutova, 2014; Chen and Otten, 2017). CT-DNAs have been found in Nicotiana (White et al, 1983; Furner et al, 1986; Chen et al, 2014), Linaria vulgaris (Matveeva et al, 2012) and Ipomoea batatas (Kyndt et al, 2015). The Plant Journal published by John Wiley & Sons Ltd and Society for Experimental Biology.
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