A wide gap exists between the rapid acceptance of genetically modified (GM) crops for cultivation by farmers in many countries and in the global markets for food and feed, and the often-limited acceptance by consumers. This review contrasts the advances of practical applications of agricultural biotechnology with the divergent paths—also affecting the development of virus resistant transgenic crops—of political and regulatory frameworks for GM crops and food in different parts of the world. These have also shaped the different opinions of consumers. Important factors influencing consumer’s attitudes are the perception of risks and benefits, knowledge and trust, and personal values. Recent political and societal developments show a hardening of the negative environment for agricultural biotechnology in Europe, a growing discussion—including calls for labeling of GM food—in the USA, and a careful development in China towards a possible authorization of GM rice that takes the societal discussions into account. New breeding techniques address some consumers’ concerns with transgenic crops, but it is not clear yet how consumers’ attitudes towards them will develop. Discussions about agriculture would be more productive, if they would focus less on technologies, but on common aims and underlying values.

A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Escherichia coil and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgot. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K + ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K+-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K+-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K + ions with compounds that are less deleterious tk)r the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.

Evolution is based on genetic variability and subsequent phenotypic selection. Mechanisms that modulate the rate of mutation according to environmental cues, and thus control the balance between genetic stability and flexibility, might provide a distinct evolutionary advantage 1-4 . Stress-induced mutations stimulated by unfavorable environments, and possible mechanisms for their induction, have been described for several organisms 2-4 , but research in this area has mainly focused on microorganisms. We have analyzed the influence of adverse environmental conditions on the genetic stability of the higher plant Arabidopsis thaliana. Here we show that a biotic stress factorattack by the oomycete pathogen Peronospora parasiticacan stimulate somatic recombination in Arabidopsis. The same effect was observed when plant pathogen-defense mechanisms were activated by the chemicals 2,6-dichloroisonicotinic acid (INA) or benzothiadiazole (BTH), or by a mutation (cim3). Together with previous studies of recombination induced by abiotic factors, these findings suggest that increased somatic recombination is a general stress response in plants. The increased genetic flexibility might facilitate evolutionary adaptation of plant populations to stressful environments.In plants, somatic recombination events are an important cause of genetic variability 5 , and, as plants lack a predetermined germ line, may also affect genetic composition of the progeny 6 . A variety of genotoxic factors, such as DNA-damaging chemicals, γ-irradiation and UV-B irradiation 7-10 , stimulate somatic recombination, an important pathway for the repair of DNA lesions in plants 5 . In addition, abiotic stress factors like heat and increased salinity seem to increase somatic recombination 7,8 . It is not known, however, whether biotic stress affects recombination and whether increased recombination might therefore be a general stress response in plants. We examined whether exposure to pathogens, a major biotic stress factor for plants, affects plant genome stability. To measure somatic recombination in whole plants, we used Arabidopsis lines carrying reporter transgenes that allowed visual detection of recombination events (Fig. 1) [8][9][10][11][12] . By testing populations of genetically identical plants grown under different conditions, this quantitative assay allowed us to determine the average recombination frequency per plant at the reporter gene locus and thus measure the influence of pathogen stress on genome stability.We sprayed seedlings of Arabidopsis recombination reporter line 651 (ref. 8) with a spore suspension of P. parasitica isolate EMWA 13 , which resulted in localized necrotic lesions at the points of attempted penetration but no further proliferation of the pathogen, as detected by microscopic observation (data not shown). This suggests the activation of plant defense mechanisms [14][15][16] . There was no macroscopic difference in appearance or growth of infected or uninfected plants. The infected plants showed a significant (P<0.0...

Chromosomal double-strand DNA breaks must be repaired; in the absence of repair the resulting acentromeric (and telomereless) fragments may be lost and/or the broken DNA ends may recombine causing general chromosomal instability. The Rad50/Mre11/Xrs2 protein complex acts at DNA ends and is implicated in both homologous and non-homologous recombination. We have isolated a rad50 mutant of the plant Arabidopsis thaliana and show here that it has a somatic hyper-recombination phenotype in planta. This finding supports the hypothesis of a competition between homologous and illegitimate recombination in higher eukaryotes. To our knowledge, this is the first direct in vivo support for the role of this complex in chromosomal recombination in a multicellular organism and the first description of a mutation of a known gene leading to hyper-recombination in plants.

Expression of the Escherichia coli proU operon, which encodes an efficient uptake system for the osmoprotectant glycine betaine, is strongly increased in cells grown at high osmolarity. We isolated 182 independent spontaneous mutants with elevated expression of the chromosomal 4'lproV-lacZ) (Hyb2) fusion at low osmolarity. Genetic analysis demonstrated that eight of these mutant strains carried mutations closely linked to the fusion, whereas all others carried mutations that appeared to be in osmZ. All of the mutations resulted in increased but still osmoregulated expression of the fI(proV-lacZ)(Hyb2) fusion. The proU-linked mutants carried an identical point mutation (proU603) which changes the -35 sequence of the proU promoter from TTGCCT to TTGACT and thereby increases the homology of the -35 region to the consensus sequence (TTGACA) of E. coli promoters. We also selected for mutants with decreased expression of the plasmid Escherichia coli and Salmonella typhimurium can adapt to high-osmolarity growth conditions by a variety of mechanisms (for recent overviews, see references 8 and 55). One of these mechanisms is the intracellular accumulation of the osmoprotectant glycine betaine, which is either synthesized from exogenously provided choline (28) or taken up from the environment (43). Two glycine betaine porters have been identified: the low-affinity ProP system (5, 32, 34) and the high-affinity ProU system (2,6,24,32).ProU is a binding-protein-dependent transport system and is encoded by the proU operon, which consists of three structural genes, proV, proW, and proX (20, 31, 41, 52). The level of proU expression is sensitively determined by the osmolarity of the growth medium. The basal transcription of proU is very low and is strongly stimulated upon a sudden osmotic upshock. The increased steady-state level of proU expression during growth at elevated osmolarity is directly correlated with the osmolarity of the growth medium (3,6,8,13,19,21,32

Impeded DNA replication or a deficiency of its control may critically threaten the genetic information of cells, possibly resulting in genome alterations, such as gross chromosomal translocations, microsatellite instabilities, or increased rates of homologous recombination (HR). We examined an Arabidopsis thaliana line derived from a forward genetic screen, which exhibits an elevated frequency of somatic HR. These HR events originate from replication stress in endoreduplicating cells caused by reduced expression of the gene coding for the catalytic subunit of the DNA polymerase d (POLd1). The analysis of recombination types induced by diverse alleles of pold1 and by replication inhibitors allows the conclusion that two not mutually exclusive mechanisms lead to the generation of recombinogenic breaks at replication forks. In plants with weak pold1 alleles, we observe genome instabilities predominantly at sites with inverted repeats, suggesting the formation and processing of aberrant secondary DNA structures as a result of the accumulation of unreplicated DNA. Stalled and collapsed replication forks account for the more drastic enhancement of HR in plants with strong pold1 mutant alleles. Our data suggest that efficient progression of DNA replication, foremost on the lagging strand, relies on the physiological level of the polymerase d complex and that even a minor disturbance of the replication process critically threatens genomic integrity of Arabidopsis cells.

A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Escherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K+ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K(+)-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K(+)-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K+ ions with compounds that are less deleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.

The Escherichia coli proU operon encodes a high-affinity, binding-protein-dependent transport system for the osmoprotectant glycine betaine. Expression of proU is osmoregulated, and transcription of this operon is greatly increased in cells grown at high osmolarity. Characterization of the proU operon and its promoter provided results similar to those published elsewhere (Gowrishankar, 1989; Stirling et al., 1989). The previously identified proU601 mutation, which leads to increased proU expression both at low- and high osmolarity, is a G to A transition in the Pribnow box of the proU promoter, which increases the homology of the -10 region to the consensus sequence of E. coli promoters. Using an antiserum raised against a ProV-beta-galactosidase hybrid protein, we have identified ProV as a protein associated with the cytoplasmic membrane. This cellular location is consistent with its proposed role as the energy-coupling component of the ProU transport system.