No abstract

No abstract

A carotenoid biosynthesis gene cluster for the production of astaxanthin was isolated from the marine bacterium Agrobacterium aurantiacum. This cluster contained five carotenogenic genes with the same orientation, which were designated crtW, crtZ, crtY, crtI, and crtB. The stop codons of individual crt genes except for crtB overlapped the start codons of the following crt genes. Escherichia coli transformants carrying the Erwinia uredovora carotenoid biosynthesis genes provide suitable substrates for carotenoid biosynthesis. The functions of the five crt genes of A. aurantiacum were determined through chromatographic and spectroscopic analyses of the pigments accumulated in some E. coli transformants carrying various combinations of the E. uredovora and A. aurantiacum carotenogenic genes. As a result, the astaxanthin biosynthetic pathway is proposed for the first time at the level of the biosynthesis genes. The crtW and crtZ gene products, which mediated the oxygenation reactions from ␤-carotene to astaxanthin, were found to have low substrate specificity. This allowed the production of many presumed intermediates of astaxanthin, i.e., adonixanthin, phoenicoxanthin (adonirubin), canthaxanthin, 3-hydroxyechinenone, and 3-hydroxyechinenone.During the last 6 years, significant advances have been made in our understanding of the genes coding for the enzymes involved in carotenoid biosynthesis. Many carotenoid biosynthesis genes have been cloned from various organisms, and their functions have been determined (3, 54, 62). Phytoene synthase genes, which mediate the formation of the first colorless carotenoid phytoene from geranylgeranyl PP i (GGPP) (11,46,55), have been isolated from the photosynthetic bacteria Rhodobacter species (5, 31), the nonphotosynthetic bacteria Erwinia species (4,45,60) and Thermus thermophilus (20), the cyanobacterium Synechococcus sp. strain PCC7942 (11), the fungus Neurospora crassa (57), and higher plants (7,50,51,58). Many genes involved in the desaturation (dehydrogenation) steps to convert phytoene to -carotene, neurosporene, or lycopene have also been obtained from the photosynthetic bacteria Rhodobacter species (5, 6, 31), the nonphotosynthetic bacteria Erwinia species (4, 45, 60) and Myxococcus xanthus (16), the cyanobacterium Synechococcus sp. strain PCC7942 (12), the fungi N. crassa (56) and Cercospora nicotianae (15), and higher plants (8,21,48). A second desaturase gene, which mediates the desaturation reaction from -carotene to lycopene, has been obtained from the cyanobacterium Anabaena sp. strain PCC7120 (33). The genes coding for lycopene cyclase, which catalyzes the formation of a cyclic carotenoid ␤-carotene from lycopene, have been isolated from the nonphotosynthetic bacteria Erwinia species (25, 45) and the cyanobacterium Synechococcus sp. strain PCC7942 (14).Among these organisms, the carotenoid biosynthesis genes of the yellow-pigmented nonphotosynthetic soil bacteria Erwinia uredovora (45) and Erwinia herbicola (4, 22, 60) have been used most frequently in the study o...

No abstract

Arabidopsis thaliana has 11 members belonging to the typical type-B ARR (authentic response regulator) family. Among them, seven highly homologous members appear also to be conserved in rice (Oryza sativa), but others are not. It was suggested that these seven ARRs are commonly implicated as DNA-binding transcription factors in the phosphorelay-mediated cytokinin signal transduction network in higher plants. To gain an insight into the functions of the cytokinin-associated type-B ARRs, we previously investigated an arr1 arr10 arr12 triple mutant and reported that it exhibited stunted growth and abnormality in vascular development. Based on this fact, here we attempted to characterize the mutant intensively with reference to cytokinin-associated phenotypes through the life cycle. We showed that the observed cytokinin-associated phenotypes of arr1 arr10 arr12 were very severe and highly analogous to those observed for certain ahk2 ahk3 ahk4/cre1 triple mutants, which have virtually no cytokinin receptor to propagate the phosphorelay signal transduction network. Among the seven ARR members belonging to the cytokinin-associated type-B ARR subfamily, it was thus suggested that ARR1, ARR10 and ARR12 together play essential (or general) roles in cytokinin signal transduction. It is therefore conceivable that the other type-B ARRs (ARR2, ARR11, ARR14 and ARR18) might play more specific roles spatially and temporally in plants.

Summary: The polymerization of 2‐bromo‐3‐hexyl‐5‐iodothiophene (1) with isopropylmagnesium chloride and Ni(dppp)Cl2 was quenched with 5 M hydrochloric acid instead of water to yield head‐to‐tail poly(3‐hexylthiophene) (HT‐P3HT) with a very low polydispersity. The $\overline M _{\rm n}$ of the polymer was controlled by the feed ratio of 1 to Ni(dppp)Cl2. Quenching with 5 M hydrochloric acid seemed to promote protonolysis of HT‐P3HT‐Ni complexes before the coupling reaction between HT‐P3HT.GPC profiles of HT‐P3HT obtained after quenching with water and 5 M hydrochloric acid, respectively.imageGPC profiles of HT‐P3HT obtained after quenching with water and 5 M hydrochloric acid, respectively.

In the phosphorelay-mediated cytokinin signal transduction of Arabidopsis thaliana, certain members of the type-B authentic response regulator (ARR) family are implicated in the regulatory networks that are primarily propagated by the cytokinin-receptors [authentic histidine kinases (AHKs)]. Clarification of the involvement of each type-B ARR transcription factor in cytokinin-responsive phenomena is still at a very early stage. Here we analyzed the redundant function of two type-B ARR genes, ARR10 and ARR12, by constructing an arr10/arr12 double mutant. The resulting mutant plants showed stronger phenotypes with special reference to the cytokinin action in roots (e.g. inhibition of root elongation, green callus formation from root explants) than those for each single mutant, suggesting that ARR10 and ARR12 redundantly play an important role in the cytokinin signaling in roots. This idea was further supported by results from root-specific microarray analyses with the double mutant plant. We also showed that ARR10 and ARR12 are involved in the AHK-dependent signaling pathway that negatively regulates protoxylem specification in root vascular tissues. When the double mutant is combined with an arr1 allele, the resultant arr1/arr10/arr12 triple mutant showed phenotypes displaying a very poor growth, quite similar to those of the wooden leg (wol) mutant that virtually lacks cytokinin receptor activities in plants. In this triple arr mutant, the specification of root vascular tissues is also affected as severely as in wol. Taken together, we propose that ARR10 and ARR12, together with ARR1, redundantly play pivotal roles in the AHK-dependent phosphorelay signaling in response to cytokinin in roots.

Poly(p-benzamide)s 1 bearing a chiral side chain on the nitrogen atom were synthesized by chain-growth polycondensation methodology. The polyamides exhibited well-defined molecular weights with narrow polydispersities. Solutions of the polyamides in several organic solvents (CH(3)CN, CHCl(3), and CH(3)OH) showed dispersion type CD signals characteristic of coupled-oscillator and much larger as compared with the corresponding monomer. The CD signals were dependent on the temperature and molecular weight of the polyamides but independent of the solvent, as far as examined. An exciton model analysis of the absorption and CD spectra provided a clear-cut picture for the secondary structure of these polyamides in solution that the N-alkylated poly(p-benzamide)s possess a right-handed helical conformation ((P)-helix). In the solid states, the results of X-ray crystallographic analysis of 4-(methylamino)benzoic acid oligomers substantiated that they have a helical conformation with three monomer units per turn.