Biomedical subjects

Mitsuo Omura

Publications and source records attributed to Mitsuo Omura.

4 recordsLinked to original sources

PubMed2005

Ectopic expression of an FT homolog from citrus confers an early flowering phenotype on trifoliate orange (Poncirus trifoliata L. Raf.).

Citrus FT (CiFT) cDNA, which promoted the transition from the vegetative to the reproductive phase in Arabidopsis thaliana, when constitutively expressed was introduced into trifoliate orange (Poncirus trifoliata L. Raf.). The transgenic plants in which CiFT was expressed constitutively showed early flowering, fruiting, and characteristic morphological changes. They started to flower as early as 12 weeks after transfer to a greenhouse, whereas wild-type plants usually have a long juvenile period of several years. Most of the transgenic flowers developed on leafy inflorescences, apparently in place of thorns; however, wild-type adult trifoliate orange usually develops solitary flowers in the axils of leaves. All of the transgenic lines accumulated CiFT mRNA in their shoots, but there were variations in the accumulation level. The transgenic lines showed variation in phenotypes, such as time to first flowering and tree shape. In F(1) progeny obtained by crossing 'Kiyomi' tangor (C. unshiu x sinensis) with the pollen of one transgenic line, extremely early flowering immediately after germination was observed. The transgene segregated in F(1) progeny in a Mendelian fashion, with complete co-segregation of the transgene and the early flowering phenotype. These results showed that constitutive expression of CiFT can reduce the generation time in trifoliate orange.

Agrobacterium tumefaciens↗

PubMed2004

Characterization of gamma-terpinene synthase from Citrus unshiu (Satsuma mandarin).

Gamma-terpinene is a monoterpene and a major component of essential oils made from citrus fruits and shows strong antioxidant activity in various assay systems. Plant gamma-terpinene synthase is a member of the monoterpene cyclase family, which produces a specific monoterpene through cyclization of geranyl diphosphate (GPP), but the monoterpene cyclases have not been fully characterized. It is necessary to prepare large amounts of gamma-terpinene synthase from Citrus unshiu (Satsuma mandarin) for the characterization, on this purpose we expressed the protein in Escherichia coli (E. coli) cells. As most monoterpene synthases have plastid-targeting signals, a gene lacking these signals was prepared and functionally expressed in E. coli cells harboring extra copies of the argU gene. The purified enzyme was incubated with GPP and the main product was confirmed to be gamma-terpinene by GC/MS.

Alkyl and Aryl Transferases↗

PubMed2002

Flavonol synthase gene expression during citrus fruit development.

We isolated a cDNA clone (CitFLS) encoding flavonol synthase (FLS) from the satsuma mandarin (Citrus unshiu Marc.) fruit and investigated the steady state of CitFLS RNA expression during the fruit development. The CitFLS was 1274 bp long, encoded 335 amino acid residues, and belonged to a family of 2-oxoglutarate-dependent dioxygenases. The level of CitFLS transcript was higher in the young leaves than in the old leaves, and it was high at the early developmental stage and low at the mature stage in the juice sacs/segment epidermis (edible part). On the other hand, the CitFLS transcript increased in the peel during fruit maturation. These results indicated that the satsuma mandarin CitFLS was differentially regulated in the developmental stage and in a tissue-specific manner. Additionally, satsuma mandarin peel tissues produced rutin (a flavonol glycoside) from an exogenous dihydroquercetin (taxifolin), indicating the ability of these tissues to produce flavonols.

Journal Article↗

PubMed2002

Analysis of sucrose synthase genes in citrus suggests different roles and phylogenetic relationships.

The purpose of this work was 2-fold; first, a molecular/evolutionary characterization of three sucrose synthase genes from citrus, and second, an analysis of their differential expression related to potential physiological function. Three non-allelic genes (CitSUS1, CitSUSA and CitSUS2) encoding sucrose synthase were isolated from citrus fruit (Citrus unshiu Marc.). Phylogenetic analysis from the deduced amino acid sequences showed that CitSUS1 and CitSUS2 could be classified into a dicot group. However, CitSUSA, together with Arabidopsis SSA, sugar beet SS and pea SusA defined another dicot group designated SUSA. Unlike other dicot sucrose synthases, these show a distinctive, monocot-like arrangement of introns and exons. The CitSUS1 and CitSUSA were also differentially expressed in leaf, flower and fruit tissues. Contrasting expression patterns were observed for CitSUS1 and CitSUSA in edible tissue (juice sacs/segment epidermis) and peel tissue (albedo/flavedo) of fruit: CitSUS1 mRNA levels decreased throughout fruit development, whereas those of CitSUSA increased. Various sugars also influenced the transcript levels of the CitSUS1 and CITSUSA: These results indicate that the CitSUS1 and CitSUSA genes for sucrose synthase in citrus differ markedly in their molecular structure and potential physiological roles. Sucrose synthase activity in edible tissue was high in the early stages and decreased until mid-develoment, then rapidly increased during maturation. The increase in activity during maturation paralleled that of sucrose accumulation. This result suggests that sucrose synthase has important roles on sugar metabolism when sucrose is accumulated in fruit.

Citrus↗