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The methylation of myo-inositol forms O-methyl inositol (D-ononitol) when plants are under abiotic stress in a reaction catalyzed by myo-inositol methyltransferase (IMT). D-Ononitol can serve as an osmoprotectant that prevents water loss in plants. We isolated the IMT cDNA from Glycine max and found by RT-PCR analysis that GmIMT transcripts are induced by drought and salinity stress treatments in the leaves of soybean seedlings. We confirmed the protein product of GmIMT and its substrate using a recombinant system in E. coli. Transgenic Arabidopsis plants over-expressing GmIMT displayed improved tolerance to dehydration stress treatment and to a lesser extent high salinity stress treatment. These results indicate that GmIMT is functional in heterologous Arabidopsis plants.

IntroductionStreptomycetes is a group of gram-positive and filamentous soil bacteria with a unique and complex differentiation process that includes simultaneous morphological (sporulation) and physiological (secondary metabolism) differentiation. Many scientific findings have elucidated that the two differentiation processes are genetically closely related and thus controlled concurrently by many regulatory factors. Generally, genes for secondary metabolite formation and morphological differentiation are clustered in the chromosome, and their expression is precisely controlled by a pathway-specific regulatory gene(s) within the cluster as well as by global regulatory genes [1][2][3].Several classes of mutants that simultaneously block the synthesis of more than one antibiotic constitute a good genetic evidence of a global regulatory system. Streptomyces coelicolor has been known to produce four genetically and structurally distinct antibiotics: the pigmented antibiotics actinorhodin and undecylprodigiosin and the unpigmented antibiotics methylenomycin and CDA (Ca 2+ -dependent antibiotic) [4]. According to an S. coelicolor genome sequence analysis, 18 gene clusters are expected to code exclusively for enzymes characteristic of its secondary metabolism [5]. abs (antibiotic synthesis deficient) mutants, for example, affect global regulatory genes involved only in physiological differentiation. Among them, absmutations absA -, absB -, and absCwere found to lack all four antibiotics, but retained normal sporulation. The molecular nature of the absA1/A2 gene products that can restore the bacterial ability for biosynthesizing all four antibiotics was identified as a two-component regulatory system, composed by the sensor histidine kinase AbsA1 and the aspartate kinase response regulator AbsA2 [4]. The phosphorylated AbsA2 is known to act as a global negative regulator of antibiotic biosynthesis in S.Streptomyces coelicolor is a filamentous soil bacterium producing several kinds of antibiotics. S. coelicolor abs8752 is an abs (antibiotic synthesis deficient)-type mutation at the absR locus; it is characterized by an incapacity to produce any of the four antibiotics synthesized by its parental strain J1501. A chromosomal DNA fragment from S. coelicolor J1501, capable of complementing the absphenotype of the abs8752 mutant, was cloned and analyzed. DNA sequencing revealed that two complete ORFs (SCO6992 and SCO6993) were present in opposite directions in the clone. Introduction of SCO6992 in the mutant strain resulted in a remarkable increase in the production of two pigmented antibiotics, actinorhodin and undecylprodigiosin, in S. coelicolor J1501 and abs8752. However, introduction of SCO6993 did not show any significant difference compared to the control, suggesting that SCO6992 is primarily involved in stimulating the biosynthesis of antibiotics in S. coelicolor. In silico analysis of SCO6992 (359 aa, 39.5 kDa) revealed that sequences homologous to SCO6992 were all annotated as hypothetical proteins. Although a metall...

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