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91.
92.
A denitrifying phototroph, Rhodobacter sphaeroides f. sp. denitrificans, has the ability to denitrify by respiring nitrate. The periplasmic respiratory nitrate reductase (Nap) catalyses the first step in denitrification and is encoded by the genes, napKEFDABC. By assaying the ss-galactosidase activity of napKEFD-lacZ fusions in wild type and nap mutant cells grown under various growth conditions, the environmental signal for inducing nap expression was examined. Under anoxic conditions with nitrate, nap genes expression in the wild-type strain was highest in the dark, and somewhat lowered by incident light, but that of the napA, napB, and napC mutant strains was low, showing that nap expression is dependent on nitrate respiration. Under oxic conditions, both the wild type and nap mutant cells showed high ss-galactosidase activities, comparable to the wild-type grown under anoxic conditions with nitrate. Myxothiazol, a specific inhibitor of the cytochrome bc (1) complex, did not affect the beta-galactosidase activity in the wild-type cells grown aerobically, suggesting that the redox state of the quinone pool was not a candidate for the activation signal for aerobic nap expression. These results suggested that the trans-acting regulatory signals for nap expression differ between anoxic and oxic conditions. Deletion analysis showed that the nucleotide sequence from -135 to -88 with respect to the translational start point is essential for nap expression either under anoxic or oxic conditions, suggesting that the same cis-acting element is involved in regulating nap expression under either anoxic with nitrate or oxic conditions. 相似文献
93.
To elucidate the mechanism of root formation in tooth development, we examined the role of insulin-like growth factor I (IGF-I) on early root formation in mandibular first molar teeth from 5-day-old mice. Immunohistochemistry revealed the specific localization of the IGF-I receptor in Hertwigs epithelial root sheath (HERS) in the tooth root. The effect of IGF-I on root development, especially on HERS, was subsequently examined in vitro. The control culture showed normal development of HERS and the periodontium, resembling that in vivo. However, the presence of 100 ng/ml IGF-I resulted in elongation of HERS and increased cell proliferation in its outer layer. These effects were negated by the addition of antibodies specific for IGF-I. Thus, we propose that IGF-I is involved in early root formation by regulating the mitotic activity in the outer layer of HERS.This study was partly supported by grants to N.F. from KAKENHI (no. 13671909), to N.F. and M.J.T. from the Promotion of 2001-Multidisciplinary Research Projects in 2001–2005, and to N.F. and K.I. from Iwate Medical University—Keiryokai Research Foundation (no. 64). 相似文献
94.
Plants have mechanisms for repairing and tolerating detrimental effects by various DNA damaging agents. A tolerance pathway that has been predicted to be present in higher plants is translesion synthesis (TLS), which is catalyzed by polymerases. In Arabidopsis (Arabidopsis thaliana), however, the only gene known to be involved in TLS is the Arabidopsis homolog of REV3, AtREV3, which is a putative catalytic subunit of Arabidopsis DNA polymerase zeta. A disrupted mutant of AtREV3, rev3, was previously found to be highly sensitive to ultraviolet-B (UV-B) and various DNA damaging agents. REV1 and REV7 are thought to be components of translesion synthesis in plants. In this study, we identified the Arabidopsis homologs of REV1 and REV7 (AtREV1 and AtREV7). Several mutants carrying disrupted AtREV1 and AtREV7 genes were isolated from Arabidopsis T-DNA-inserted lines. An AtREV1-disrupted mutant, rev1, was found to be moderately sensitive to UV-B and DNA cross-linkers. A rev1rev3 double mutant, like rev3, showed high sensitivity to UV-B, gamma-rays, and DNA cross-linkers. An AtREV7-disrupted mutant, rev7, was possibly sensitive to cis-diamminedichloroplatinum(II), a kind of DNA cross-linker, but it was not sensitive to acute UV-B and gamma-ray irradiation. On the other hand, the aerial growth of rev7, like the aerial growth of rev1 and rev3, was inhibited by long-term UV-B. These results suggest that a TLS mechanism exists in a higher plant and show that AtREV1 and AtREV7 have important roles in tolerating exposure to DNA-damaging agents. 相似文献
95.
l-Galactono-1,4-lactone dehydrogenase (GalLDH; EC 1.3.2.3) is the last enzyme in the putative l-ascorbic acid (AsA) biosynthetic pathway of plants. Here, we show for the first time that the overexpression of GalLDH can increase AsA content in tobacco (Nicotiana tabacum L.) BY-2 cells. To see the effect, we analyzed the properties of these AsA-overproducing transgenic cell lines, especially in relation to AsA content of cells, cell division, senescence and resistance to oxidative stress. The mitotic index in AsA-overproducing cells was higher than in wild-type cells. Moreover, the browning of these cells was markedly restrained, and the proportion of dead cells was reduced, especially in the later period of culture. These AsA-overproducing cells also acquired resistance to paraquat (methyl viologen), which produces active oxygen species. These results contribute to the previous insights about AsA and raise the possibility of the generation of plants that have resistance to environmental stresses by increasing their AsA content. 相似文献
96.
Shimoda Y Nagata M Suzuki A Abe M Sato S Kato T Tabata S Higashi S Uchiumi T 《Plant & cell physiology》2005,46(1):99-107
We characterized the expression profiles of LjHb1 and LjHb2, non-symbiotic hemoglobin (non-sym-Hb) genes of Lotus japonicus. Although LjHb1 and LjHb2 showed 77% homology in their cDNA sequences, LjHb2 is located in a unique position in the phylogenetic tree of plant Hbs. The 5'-upstream regions of both genes contain the motif AAAGGG at a position similar to that in promoters of other non-sym-Hb genes. Expression profiles obtained by using quantitative RT-PCR showed that LjHb1 and LjHb2 were expressed in all tissues of mature plants, and expression was enhanced in mature root nodules. LjHb1 was strongly induced under both hypoxic and cold conditions, and by the application of nitric oxide (NO) donor, whereas LjHb2 was induced only by the application of sucrose. LjHb1 was also induced transiently by the inoculation with the symbiotic rhizobium Mesorhizobium loti MAFF303099. Observations using fluorescence microscopy revealed the induction of LjHb1 expression corresponded to the generation of NO. These results suggest that non-sym-Hb and NO have important roles in stress adaptation and in the early stage of legume-rhizobium symbiosis. 相似文献
97.
Seven Lotus japonicus genes required for transcriptional reprogramming of the root during fungal and bacterial symbiosis 总被引:7,自引:0,他引:7 下载免费PDF全文
Kistner C Winzer T Pitzschke A Mulder L Sato S Kaneko T Tabata S Sandal N Stougaard J Webb KJ Szczyglowski K Parniske M 《The Plant cell》2005,17(8):2217-2229
98.
Shimada N Sasaki R Sato S Kaneko T Tabata S Aoki T Ayabe S 《Journal of experimental botany》2005,56(419):2573-2585
Dihydroflavonol 4-reductase (DFR) is the first committed enzyme of the anthocyanin and condensed tannin pathways. Several DFR cDNAs have been cloned, and different specificities of DFR isozymes in the substrate hydroxylation patterns have been reported, but only fragmentary knowledge of DFR gene organization is available. Reported here is a comprehensive analysis of DFRs of a model legume, Lotus japonicus. A total of five DFR genes were found to form a cluster within a 38 kb region in the L. japonicus genome, whereas six cDNAs, including two splicing variants resulting from a transversion at a splicing acceptor site, were cloned. All the genes were expressed, with different organ specificities, in the mature plant. Three of the DFR proteins heterologously expressed in Escherichia coli showed catalytic activity, and their substrate preferences agreed with the variation of a specific active site residue (Asp or Asn) reported to control the specificity. The hydroxylation patterns of anthocyanidins and condensed tannin units in the stems did not reflect the substrate specificity of the expressed isozymes, implying complex regulation mechanisms in the biosynthesis. The two splicing variants and one DFR with Ser at the specificity-controlling position failed to show the activity, but a revertant protein replacing the unusual splicing restored the activity. The phylogenetic tree, constructed with known DFR sequences, showed evolutionary divergence of some of the DFR genes prior to the plant speciation. This work affords the basis for genetic and biochemical studies on the diversity of DFR and the flavonoid products. 相似文献
99.
100.
Ojima K Breitenbach J Visser H Setoguchi Y Tabata K Hoshino T van den Berg J Sandmann G 《Molecular genetics and genomics : MGG》2006,275(2):148-158
A gene has been cloned from Xanthophyllomyces dendrorhous by complementation of astaxanthin formation in a β-carotene accumulating mutant. It consists of 3,166 bp and contains 17
introns. For the β-carotene mutant ATCC 96815, a single point mutation in the splicing sequence of intron 8 was found. The
resulting improper splicing of the mRNA results in an inactive protein. The cDNA of this β-carotene oxygenase encodes a cytochrome
P450 monooxygenase belonging to the 3A subfamily. P450-specific domains were identified including a cytochrome P450 and an
oxygen binding motif. Electrons are provided by a cytochrome P450 reductase. Functional characterization of the enzyme by
genetic modification of X. dendrorhous demonstrated that this P450 monooxygenase is multifunctional catalyzing all steps from β-carotene to astaxanthin formation
by oxygenation of carbon 3 and 4. The reaction sequence is first 4-ketolation of β-carotene followed by 3-hydroxylation. A
hydroxylation mechanism at allylic carbon atoms has been proposed for the generation of 4-keto and 3-hydroxy groups at both
β-ionone ends. 相似文献