Pageni, B. B., Lupwayi, N. Z., Larney, F. J., Kawchuk, L. M. and Gan, Y. 2013. Populations, diversity and identities of bacterial endophytes in potato ( Solanum tuberosum L.) cropping systems. Can. J. Plant Sci. 93: 1125–1142. Most plants host endophytic bacteria, but their identities and functions are usually unknown. Bacterial endophytes associated with potato grown after dry bean (Phaseolus vulgaris L.) or wheat (Triticum aestivum L.) were isolated, quantified and identified in a field study that compared crop rotations (3 to 6 yr in length) and soil management (CONV, conventional; CONS, conservation) for dry bean, potato, sugar beet (Beta vulgaris L.) and spring wheat. Populations of culturable endophytes ranged from 2.83×103 to 7.65×103 colony-forming units g−1 of root dry matter. The populations and diversity of the endophytes were greater with CONS than CONV soil management, and tended to be greater in longer than shorter rotations. The community structures of the endophytes were different between CONV and CONS soil management. A terminal-restriction fragment length polymorphism assay targeting the 16S rRNA gene, and its sequencing, showed that CONS management systems contained more Proteobacteria than CONV management systems, and vice-versa for Acidobacteria. Bacteriodetes were found only in long CONS rotations. This phylogenetic characterization of potato endophytes is important for further studies on their effects on the host plants.
The gene cluster of calicheamicin contains calS9, which encodes UDP-GlcA decarboxylase that converts UDP-GlcA to UDP-xylose. calS9 was cloned in pET32a(+) and expressed in Escherichia coli BL21 (DE3) to characterize its putative function. The reaction product was analyzed by high-performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry. The deoxysugar biosynthesis of Streptomyces sp. KCTC 0041BP was inactivated by gene replacement to generate Streptomyces sp. GerSM2 mutant, which was unable to produce dihydrochalcomycin. calS7, calS8, and calS9 UDP-xylose biosynthetic genes were cloned in an integrative plasmid pSET152 to generate pBPDS, which was heterologously expressed in Streptomyces sp. GerSM2. Finally, novel glycosylated product, 5-O-xylosyl-chalconolide derivative, in the conjugal transformants was isolated and analyzed by HPLC and liquid chromatography-mass spectrometry.
Dry bean (Phaseolus vulgaris L.) is usually considered to be poor at biological nitrogen fixation (BNF), but large variations in this trait have been observed among bean genotypes. We evaluated 16 bean genotypes for N2 fixation ability in four N treatments: (i) uninoculated in low-N soil (30 kg N ha−1), (ii) inoculated with commercial Rhizobium leguminosarum bv. phaseoli inoculant Nitrastik-D® in low-N soil, (iii) inoculated with commercial R. leguminosarum bv. phaseoli inoculant Nodulator® in low-N soil, and (iv) uninoculated in high-N soil (100 kg N ha−1). There were differences between genotypes in all the plant parameters that were measured, but only nodulation was affected by N treatment. The 100 kg N ha−1 treatment suppressed nodulation. Seven genotypes nodulated well with either inoculant, two genotypes nodulated better with Nitrastik-D than with Nodulator, three nodulated better with Nodulator than with Nitrastik-D, and four nodulated poorly with either inoculant. Cultivars AC Redbond, Island, and Resolute, all currently commercially grown, did not fix much N2 at flowering (4–8 kg N ha−1) or maturity (19–34 kg N ha−1). By contrast, germplasm lines PI 136692 (red bean), GH-196 (pinto bean), and LEF2RB (carioca bean) had high BNF capability at flowering (10–11 kg N ha−1) and especially at maturity (60–72 kg N ha−1), in addition to high seed yield (2778–2897 kg ha−1), indicating their superior ability to support both of these economically important traits throughout plant growth. These three genotypes would be valuable to breeders for the genetic improvement of BNF in dry bean cultivars.
Through an inactivation experiment followed by complementation, the gerGTII gene was previously characterized as a chalcosyltransferase gene involved in the biosynthesis of dihydochalcomycin. The glycosyltransferase gerGTI was identified as a deoxyallosyltransferase required for the glycosylation of D-mycinose sugar. This 6-deoxyhexose sugar was converted to mycinose, via bis-O-methylation, following attachment to the polyketide lactone during dihydrochalcomycin biosynthesis. Gene sequence alignment of gerGTI to several glycosyltransferases revealed a consensus sequence motif that appears to be characteristic of the enzymes in this sub-group of the glycosyltransferase family. To characterize its putative function, genetic disruption of gerGTI in the wild-type strain Streptomyces sp. KCTC 0041BP and in the gerGTII-deleted mutant (S. sp. Delta gerGTsss, as well as complementation of gerGTII in S. sp. Delta gerGTss-GTs, were carried out, and the products were analyzed by LC/MS. S. sp. Delta gerGTss-GTs mutant produced dihydrochalconolide macrolide. S. sp. Delta gerGTs and S. sp. Delta gerGTss-GTs complementation of gerGTII yielded dihydrochalconolide without the mycinose sugar. The intermediate shows that gerGTI encodes a deoxyallosyltransferase that acts after gerGTII.
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