Stress-induced intrachromosomal recombination in plant somatic cells.

Abstract

Levels of induced homologous recombination between chromosomal repeats in plant somatic cells were examined. Transgenic plants of Nicotiana tabacum hemi-or homozygous for pairs of deletion derivatives of the neomycin phosphotransferase (nptI) marker gene integrated at a single genomic locus were produced. Homologous recombination within the overlapping parts of the nptll gene restored the function and the resulting kanamycin resistance was used for scoring recombination frequency. The recombination events were confirmed by the appearance of a characteristic 1245-base-pair EcoRV fragment detected in all kanamycin-resistant clones tested. The rate of spontaneous recombination was found to be related to the copy number of recombination substrates and was 9 x 10-5 and 19 x 10-5 for hemi-and homozygote strains, respectively. Ionizing radiation, mitomycin C, and heat shock markedly increased the frequency of intrachromosomal recombination. Low doses of x-rays (1.25 Gy) enhanced the relative recombination frequency to approximately twice the spontaneous value. The presence of mitomycin C increased the frequency of recombination 9-fold and exposure to an elevated temperature (50°C) increased it 6.5-fold. The x-ray and heat shock treatments reduced cell viability to 53% and 8%, respectively. Mitomycin C treatment had no effect on cell survival.

Arabidopsis thaliana mutants altered in homologous recombination

“…It has been shown that in plants homologous recombination can be stimulated by genomic stress caused by x-rays, mitomycin C, and MMS treatments (9)(10)(11). This indicates that homologous recombination is involved, at least in part, in the repair of the DNA damage caused by these agents.…”

“…As in other organisms (5), the frequency of meiotic recombination in plants is influenced by environmental factors (6), sequence diversity in interspecific crosses (7), and the direction of crossing (8). In somatic cells, rates of homologous recombination can be stimulated by DNA-damaging treatments (9)(10)(11). This also has been observed in bacteria, yeast, and mammalian cells (12).…”

“…Mutant xrs11 showed unaltered levels of homologous recombination under standard assay conditions but was unable to respond to stimulation of recombination by x-ray irradiation. Because such an increase in somatic recombination is a reaction to genomic and environmental stresses (10,11), xrs11 may be affected in the transduction of signals linking DNA damage to proper cellular responses (31) rather than in the recombination process itself. It resembles yeast DUN kinase mutation, which renders cells sensitive to hydroxyurea, UV, and MMS, and abolishes specific activation of DNA damageinducible genes (32).…”

“…Somatic recombination can be stimulated by genomic and͞or environmental stress (10,11). X-rayinduced recombination in the wild type and mutants was compared by applying x-ray doses (20 -60 Gy) as single or multiple treatments before transformation with the recombination substrates.…”

“…This feature may be relevant for the late differentiation of germ cells in plants and the potential transmission of somatic recombination events to the germ-line (14,15). Interestingly, genomic changes are influenced by environmental stresses (16,17), and specific induction of intrachromosomal homologous recombination by heat and salt stress has been documented (10,11). Thus, regulation of genome stability during plant development is especially important.…”