Nucleotide polymorphism affecting FLC expression underpins heading date variation in horticultural brassicas

Variation in flowering time and response to overwintering has been exploited to breed brassica vegetables that can be harvested year‐round. Our knowledge of flowering time control now enables the investigation of the molecular basis of this important variation. Here, we show that a major determinant of heading date variation in Brassica oleracea is from variation in vernalization response through allelic variation at FLOWERING LOCUS C.C2 (BoFLC4). We characterize two alleles of BoFLC.C2 that are both functional and confer a requirement for vernalization, but they show distinct expression dynamics in response to cold. Complementation experiments in Arabidopsis thaliana revealed that the allelic variation results from cis polymorphism at BoFLC.C2, which quantitatively influences the degree of cold‐induced epigenetic silencing. This results in one allelic variant conferring consistently later heading under both glasshouse and field conditions through reduced environmental sensitivity. Our results suggest that breeding of brassica varieties for commercially valuable variation in heading date has been achieved through the selection of cis polymorphism at FLC, similar to that underpinning natural variation in A. thaliana. This understanding will allow for the selection of alleles with distinct sensitivities to cold and robust heading dates under variable climatic conditions, and will facilitate the breeding of varieties more resistant to climate change.     

Raman spectroscopy predicts the link between claw keratin and bone collagen structure in a rodent model of oestrogen deficiency

Osteoporosis is a common disease characterised by reduced bone mass and an increased risk of fragility fractures. Low bone mineral density is known to significantly increase the risk of osteoporotic fractures, however, the majority of non-traumatic fractures occur in individuals with a bone mineral density too high to be classified as osteoporotic. Therefore, there is an urgent need to investigate aspects of bone health, other than bone mass, that can predict the risk of fracture. Here, we successfully predicted association between bone collagen and nail keratin in relation to bone loss due to oestrogen deficiency using Raman spectroscopy. Raman signal signature successfully discriminated between ovariectomised rats and their sham controls with a high degree of accuracy for the bone (sensitivity 89%, specificity 91%) and claw tissue (sensitivity 89%, specificity 82%). When tested in an independent set of claw samples the classifier gave 92% sensitivity and 85% specificity. Comparison of the spectral changes occurring in the bone tissue with the changes occurring in the keratin showed a number of common features that could be attributed to common changes in the structure of bone collagen and claw keratin. This study established that systemic oestrogen deficiency mediates parallel structural changes in both the claw (primarily keratin) and bone proteins (primarily collagen). This strengthens the hypothesis that nail keratin can act as a surrogate marker of bone protein status where systemic processes induce changes.     

Tobacco lines with high copy number of replicating recombinant geminivirus vectors after biolistic DNA delivery

The feasibility of obtaining clonal lines with replicating, multicopy geminivirus vectors by direct DNA trans-formation of cultured tobacco cells was studied. The replicating vectors pTGA32 and pST31 are based on the tomato golden mosaic virus (TGMV) A genome and encode the neomycin phosphotransferase type II (NPT-II) enzyme that confers kanamycin resistance to plant cells. Following introduction into plant cells, unit-length viral genomes were released from the tandem repeats and replicated. In protoplasts, replication of unit-length pTGA32 and pST31 was about as efficient as replication of unit-length DNA A from plasmid pTGA26, which contains 1.5 copies of wild-type DNA A. Tobacco suspension culture cells were bombarded with the recombinant DNA A constructs and selected for kanamycin resistance. The number of kanamycin-resistant clones per bombardment was about the same when the TGMV DNA A vectors or a non-replicating plasmid (pLC14) which also encodes NPT-II was used. Replicating, unit-length DNA A in up to approximately 1000 copies per cell was found in about 10% of the kanamycin-resistant clones selected following bombardment of cells with TGMV vectors. The results suggest that geminiviruses may serve as useful multicopy vectors in cultured cells.     

Purification and properties of sulfhydryl oxidase from bovine pancreas

Immunofluorescent studies showed that antibodies prepared against bovine milk sulfhydryl oxidase reacted with acinar cells of porcine and bovine pancreas. A close inspection of the specific location within bovine pancreatic cells revealed that the zymogen granules, themselves, bound the fluorescent antibody. Bovine pancreatic tissue was homogenized in 0.3 M sucrose, then separated into the zymogen granule fraction by differential centrifugation. The intact zymogen granules were immunofluorescent positive when incubated with antibodies to bovine milk sulfhydryl oxidase, and glutathione-oxidizing activity was detected under standard assay conditions. Pancreatic sulfhydryl oxidase was purified from the zymogen fraction by precipitation with 50% saturated ammonium sulfate, followed by Sepharose CL-6B column chromatography. Active fractions were pooled and subjected to covalent affinity chromatography on cysteinylsuccinamidopropyl-glass using 2 mM glutathione as eluant at 37 degrees C. The specific activity of bovine pancreatic sulfhydryl oxidase thus isolated was 10-20 units/mg protein using 0.8 mM glutathione as substrate. Ouchterlony double-diffusion studies showed that antibody directed against the purified bovine milk enzyme reacted identically with pancreatic sulfhydryl oxidase. The antibody also immunoprecipitated glutathione-oxidizing activity from crude pancreatic homogenates. Western blotting analysis indicated a 90,000 Mr antigen-reactive band in both bovine milk and pancreatic fractions while sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single silver-staining protein with an apparent Mr 300,000. Thus, we believe that sulfhydryl oxidase may exist in an aggregated molecular form. Bovine pancreatic sulfhydryl oxidase catalyzes the oxidation of low-molecular-weight thiols such as glutathione, N-acetyl-L-cysteine, and glycylglycyl-L-cysteine, as well as that of a high-molecular-weight protein substrate, reductively denatured pancreatic ribonuclease A.     

A hybrid superoxide dismutase containing both functional iron and manganese

A hybrid superoxide dismutase containing functional Mn and Fe has been isolated from Escherichia coli. Streptomycin, which binds tightly to both the Mn- and the Fe-containing superoxide dismutases, had the expected effect on the electrophoretic and chromatographic behavior of the hybrid. Treatment of the hybrid with H2O2, which selectively inactivates the Fe-containing enzyme, resulted in partial inactivation accompanied by a resegregation of subunits, with the formation of active Mn-enzyme and inactive Fe-enzyme. A similar resegregation of subunits was observed when the hybrid was exposed to 2.5 M guanidinium chloride. Hybrids containing Mn or Fe could be generated in vitro by mixing the Mn-enzyme with the Fe-enzyme, removing metals with 8-hydroxyquinoline in the presence of 2.5 M guanidinium chloride, and then dialyzing against Mn(II) or Fe(II) salts. Ten per cent of the activity of the Fe-superoxide dismutases is resistant to H2O2, which correlates with its content of Mn. Since the activity remaining after exhaustive treatment with H2O2 exhibited the electrophoretic mobility of the Fe-enzyme, we concluded that some of the active sites of the Fe-enzyme were actually occupied by Mn. It should be noted, however, that for purposes of metal reconstitution experiments, a definite specificity was demonstrated. The Mn-enzyme was reconstituted with Mn(II), whereas the Fe-enzyme activity was recovered using only Fe(II). We propose that the Fe-superoxide dismutase may be heterogeneous and that 10% of its activity is actually due to a Mn-containing variant with the same electrophoretic mobility. Only the apohybrid enzyme regained enzymatic activity using both Mn(II) and Fe(II).