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Proc Natl Acad Sci U S A. 2015 May 5;112(18):5844-9. doi: 10.1073/pnas.1419685112. Epub 2015 Apr 20.

The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: An example of a naturally transgenic food crop.

Author information

  • 1Department of Molecular Biotechnology, Ghent University, 9000 Ghent, Belgium;
  • 2Department of Molecular Biotechnology, Ghent University, 9000 Ghent, Belgium; International Potato Center, Lima 12, Peru;
  • 3Beijing Key Laboratory of Crop Genetic Improvement/Laboratory of Crop Heterosis and Utilization, Ministry of Education, China Agricultural University, Beijing, China, 100193; and.
  • 4Plant Genetic Resources Unit, US Department of Agriculture, Agricultural Research Service, Griffin, GA 30223.
  • 5International Potato Center, Lima 12, Peru;
  • 6International Potato Center, Lima 12, Peru; j.kreuze@cgiar.org.

Abstract

Agrobacterium rhizogenes and Agrobacterium tumefaciens are plant pathogenic bacteria capable of transferring DNA fragments [transfer DNA (T-DNA)] bearing functional genes into the host plant genome. This naturally occurring mechanism has been adapted by plant biotechnologists to develop genetically modified crops that today are grown on more than 10% of the world's arable land, although their use can result in considerable controversy. While assembling small interfering RNAs, or siRNAs, of sweet potato plants for metagenomic analysis, sequences homologous to T-DNA sequences from Agrobacterium spp. were discovered. Simple and quantitative PCR, Southern blotting, genome walking, and bacterial artificial chromosome library screening and sequencing unambiguously demonstrated that two different T-DNA regions (IbT-DNA1 and IbT-DNA2) are present in the cultivated sweet potato (Ipomoea batatas [L.] Lam.) genome and that these foreign genes are expressed at detectable levels in different tissues of the sweet potato plant. IbT-DNA1 was found to contain four open reading frames (ORFs) homologous to the tryptophan-2-monooxygenase (iaaM), indole-3-acetamide hydrolase (iaaH), C-protein (C-prot), and agrocinopine synthase (Acs) genes of Agrobacterium spp. IbT-DNA1 was detected in all 291 cultigens examined, but not in close wild relatives. IbT-DNA2 contained at least five ORFs with significant homology to the ORF14, ORF17n, rooting locus (Rol)B/RolC, ORF13, and ORF18/ORF17n genes of A. rhizogenes. IbT-DNA2 was detected in 45 of 217 genotypes that included both cultivated and wild species. Our finding, that sweet potato is naturally transgenic while being a widely and traditionally consumed food crop, could affect the current consumer distrust of the safety of transgenic food crops.

KEYWORDS:

Agrobacterium spp.; food safety; horizontal gene transfer; sweet potato; transgenic crops

PMID:
25902487
PMCID:
PMC4426443
DOI:
10.1073/pnas.1419685112
[PubMed - indexed for MEDLINE]
Free PMC Article
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