title: Suppression of different classes of somatic mutations in Arabidopsis by vir gene-expressing Agrobacterium strains.
abstract: BACKGROUND
  Agrobacterium infection, which is widely used to generate transgenic plants, is often accompanied by T-DNA-linked mutations and transpositions in flowering plants. It is not known if Agrobacterium infection also affects the rates of point mutations, somatic homologous recombinations (SHR) and frame-shift mutations (FSM). We examined the effects of Agrobacterium infection on five types of somatic mutations using a set of mutation detector lines of Arabidopsis thaliana. To verify the effect of secreted factors, we exposed the plants to different Agrobacterium strains, including wild type (Ach5), its derivatives lacking vir genes, oncogenes or T-DNA, and the heat-killed form for 48 h post-infection; also, for a smaller set of strains, we examined the rates of three types of mutations at multiple time-points. The mutation detector lines carried a non-functional β-glucuronidase gene (GUS) and a reversion of mutated GUS to its functional form resulted in blue spots. Based on the number of blue spots visible in plants grown for a further two weeks, we estimated the mutation frequencies.
  
  
  RESULTS
  For plants co-cultivated for 48 h with Agrobacterium, if the strain contained vir genes, then the rates of transversions, SHRs and FSMs (measured 2 weeks later) were lower than those of uninfected controls. In contrast, co-cultivation for 48 h with any of the Agrobacterium strains raised the transposition rates above control levels. The multiple time-point study showed that in seedlings co-cultivated with wild type Ach5, the reduced rates of transversions and SHRs after 48 h co-cultivation represent an apparent suppression of an earlier short-lived increase in mutation rates (peaking for plants co-cultivated for 3 h). An increase after 3 h co-cultivation was also seen for rates of transversions (but not SHR) in seedlings exposed to the strain lacking vir genes, oncogenes and T-DNA. However, the mutation rates in plants co-cultivated for longer times with this strain subsequently dropped below levels seen in uninfected controls, consistent with the results of the single time-point study.
  
  
  CONCLUSIONS
  The rates of various classes of mutations that result from Agrobacterium infection depend upon the duration of infection and the type of pathogen derived factors (such as Vir proteins, oncoproteins or T-DNA) possessed by the strain. Strains with vir genes, including the type used for plant transformation, suppressed selected classes of somatic mutations. Our study also provides evidence of a pathogen that can at least partly counter the induction of mutations in an infected plant.
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. jas109@gmail.com.|Department of Plant Science, Central University of Kerala, Kasaragod, 671328, India. jas109@gmail.com.
authors: Jasmine M
authors: JM
authors: Shah
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. bioananthi.08@gmail.com.
authors: Anantha Maharasi
authors: AM
authors: Ramakrishnan
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. amit.mku@gmail.com.
authors: Amit Kumar
authors: AK
authors: Singh
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. whiterose.mani@gmail.com.
authors: Subalakshmi
authors: S
authors: Ramachandran
authors: Department of Environmental Science, Central University of Kerala, Kasaragod, 671328, India. unnikrishnanu@gmail.com.
authors: Unnikrishnan
authors: U
authors: Unniyampurath
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. ajithajayashankar@gmail.com.
authors: Ajitha
authors: A
authors: Jayshankar
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. nithi.bio14@gmail.com.
authors: Nithya
authors: N
authors: Balasundaram
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. shanmuhapreya@gmail.com.
authors: Shanmuhapreya
authors: S
authors: Dhanapal
authors: , 14 Randwick St, Sydney, 2031, Australia. geoffjhyde@gmail.com.
authors: Geoff
authors: G
authors: Hyde
authors: Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology-Madras, Chennai, 600036, India. rbaskar@iitm.ac.in.
authors: Ramamurthy
authors: R
authors: Baskar
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics*; D017360:Arabidopsis / Q000235:genetics*; D032461:Chromosomes, Plant / Q000235:genetics; D004926:Escherichia coli / Q000378:metabolism; D016368:Frameshift Mutation; D005798:Genes, Bacterial; D059765:Homologous Recombination / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D030821:Plants, Genetically Modified; D013489:Suppression, Genetic; D013997:Time Factors