Natural transformants of Camellia section Thea

Abstract

Horizontal gene transfer (HGT) plays an important role in plant evolution and plant development. Agrobacterium-mediated gene transfer leads to the formation of crown galls or hairy roots, due to expression of transferred T-DNA genes. Spontaneous regeneration of transformed cells can produce natural transformants carrying cellular T-DNA (cT-DNA) sequences of bacterial origin. HGT from Agrobacterium to dicots is remarkably widespread. The production of naturally genome modified plants could play a role in plant evolution and environment. Among these natural GMOs (nGMOs) there are the tea plants. Camellia sinensis var. sinensis cv. Shuchazao contains a single 5.5 kb cT-DNA fragment organized as imperfect inverted repeat with three inactive genes. 142 Camellia accessions, belonging to 10 of 11 species of the section Thea, were studied for the presence of cT-DNA alleles. All of them contain the cT-DNA insert, indicating that they are resulted from the single transformed event. Allele phasing showed that 82 accessions were heterozygous for T-DNA alleles, 60 others were homozygous. A phylogenetic analysis of all found alleles showed existence of two separate groups of them, further divided into subgroups. The alleles of the different Camellia species were distributed mosaically over groups, and different species showed very similar T-DNA alleles. This indicates that the taxonomy of Thea requires revision. The nucleotide divergence of the imperfect cT-DNA repeats indicates that the age of cT-DNA insertion is about 15 mya, which is earlier then emergence of section Thea [1]. We present a working model for the origin and evolution of nGMO plants derived from allogamous transformants.