BACTERIA THAT INDUCE MORPHOGENESIS IN ULVA PERTUSA (CHLOROPHYTA) GROWN UNDER AXENIC CONDITIONS1

Marine foliaceous green macroalgae such as Ulva lose their typical morphology when cultured aseptically in defined synthetic media. However, after reinfection by certain marine bacteria (isolated from unialgal cultures of Ulva pertusa Kjellman), the organisms regain their typical foliaceous or tubular morphology. To investigate the morphogenesis (MG) induced in U. pertusa by bacteria, we isolated and identified bacteria with MG activity on U. pertusa and studied the distribution of such bacteria in seawater and on various marine macroalgae. We isolated 1555 bacterial strains from 18 species of marine macroalgae (six Chlorophyta, five Phaeophyta, and seven Rhodophyta), from seawater and from sediment collected at the beach at Omaezaki, Shizuoka Prefecture; Japan. Of these, 676 bacterial strains (43.5%) showed MG activity. They were classified into six bacterial groups, Flavobacterium, Vibrio, Pseudomonas, Deleya, Escherichia, and gram-positive cocci. These bacteria were ubiquitous among the samples and were not specific to U. pertusa. Several plant growth regulators had no MG activity. Filter-sterilized supernatants of culture media of MG-active bacteria strains did not induce MG. Cocultivation of Ulva with active bacterial strains is so far the only way to induce the MG effect, which suggests that for MG direct contact between Ulva and the bacterial strain is necessary.     

Cloning of the polyketide synthase gene atX from Aspergillus terreus and its identification as the 6-Methylsalicylic acid synthase gene by heterologous expression

The geneCAL1 (also known asCDC43) ofSaccharomyces cerevisiae encodes the subunit of geranylgeranyl transferase I (GGTase I), which modifies several small GTPases. Biochemical analyses of the mutant enzymes encoded bycall-1, andcdc43-2 tocdc43-7, expressed in bacteria, have shown that all of the mutant enzymes possess reduced activity, and that none shows temperature-sensitive enzymatic activities. Nonetheless, all of thecall/cdc43 mutants show temperature-sensitive growth phenotypes. Increase in soluble pools of the small GTPases was observed in the yeast mutant cells at the restrictive temperature in vivo, suggesting that the yeast prenylation pathway itself is temperature sensitive. Thecall-1 mutation, located most proximal to the C-terminus of the protein, differs from the othercdc43 mutations in several respects. An increase in soluble Rholp was observed in thecall-1 strain grown at the restrictive temperature. The temperature-sensitive phenotype ofcall-1 is most efficiently suppressed by overproduction of Rholp. Overproduction of the other essential target, Cdc42p, in contrast, is deleterious incall-1 cells, but not in othercdc43 mutants or the wild-type strains. Thecdc43-5 mutant cells accumulate Cdc42p in soluble pools andcdc43-5 is suppressed by overproduction of Cdc42p. Thus, several phenotypic differences are observed among thecall/cdc43 mutations, possibly due to alterations in substrate specificity caused by the mutations.     

Occurrence of jasmonic acid in Dunaliella (Dunaliellales, Chlorophyta)

The occurrence of jasmonic acid and related compounds in Dunaliella species was investigated using gas-liquid chromatography/mass spectroscopy (GCY MS). Jasmonic acid was identified in the ethyl acetate soluble-acidic fraction of Dunaliella tertiolecta and Dunaliella salina (Dunal) Teodoresco, The concentration of jasmonic acid in D. salina. which is extremely halophilic, was much higher than that in D. tertiolecta Butcher, These results indicate that jasmonic acid might play an important role in salt-tolerance in Dunaliella.     

Metabolic inactivation of retinoic acid by a novel P450 differentially expressed in developing mouse embryos.

Retinoic acid (RA) is a physiological agent that has a wide range of biological activity and appears to regulate developmental programs of vertebrates. However, little is known about the molecular basis of its metabolism. Here we have identified a novel cytochrome P450 (P450RA) that specifically metabolizes RA. In vitro, P450RA converts all-trans RA into 5,8-epoxy all-trans RA. P450RA metabolizes other biologically active RAs such as 9-cis RA and 13-cis RA, but fails to metabolize their precursors, retinol and retinal. Overexpression of P450RA in cell culture renders the cells hyposensitive to all-trans RA. These functional tests in vitro and in vivo indicate that P450RA inactivates RA. The P450RA gene is not expressed uniformly but in a stage- and region-specific fashion during mouse development. The major expression domains in developing embryos include the posterior neural plate and neural crest cells for cranial ganglia. The expression of P450RA, however, is not necessarily inducible by excess RA. These results suggest that P450RA regulates the intracellular level of RA and may be involved in setting up the uneven distribution of active RA in mammalian embryos.     

Integration of molecular and classical linkage groups of the silkworm, Bombyx mori (n = 28).

Previously published linkage groups (LGs) composed of molecular markers were assigned to classical LGs in the silkworm, Bombyx mori (n = 28). Four markers from the classical linkage map, og, w-1, Lp, and Pfl, were assigned to the molecular linkage maps using sequence tagged sites. In addition, linkage analysis was carried out using BF1 progeny between wild-type and mutant stocks carrying morphological phenotypic markers. As a result, the counterparts for 26 of 28 molecular LGs were identified with their counterparts of the classical LGs. Two visible markers, Sel and Xan, representing different classical LGs, were found to be linked.     

Organization of Actin Filaments and Zonula Adherens during Somitogenesis in the Chick Embryo

The organization of F-actin during somitogenesis in the chick embryo was studied by use of rhodamine-conjugated phalloidin and transmission electron microscopy (TEM). Separation of a somite from the segmental plate proceeded simultaneously with the organization of segmental plate cells into a hemispherical epithelial sheet whose open side was directed antero-laterally. At the same time, intense staining of F-actin appeared in the apical surface of the epithelial sheet. Observations by TEM showed that zonulae adherentes associated with many actin filaments increased in the apical region of cells being organized into an epithelial sheet while this junctional apparatus was only sparsely distributed in the segmental plate cells. The hemispherical sheet subsequently closed to form an epithelial vesicle, with increase in curvature of its apical surface, and narrowing of cellular apices. At the same time, the zonulae adherentes and actin filaments in the cellular apices further increased, and many cellular processes formed on the apical surface of the epithelial somites. These findings suggest that segmentation involves organization of zonulae adherentes and a contractile process caused by acin filaments anchored to the zonulae adherentes.