The assembly of the FtsZ ring at the mid-chloroplast division site depends on a balance between the activities of AtMinE1 and ARC11/AtMinD1

Chloroplast division comprises a sequence of events that facilitatesymmetric binary fission and that involve prokaryotic-like stromaldivision factors such as tubulin-like GTPase FtsZ and the divisionsite regulator MinD. In Arabidopsis, a nuclear-encoded prokaryoticMinE homolog, AtMinE1, has been characterized in terms of itseffects on a dividing or terminal chloroplast state in a limitedseries of leaf tissues. However, the relationship between AtMinE1expression and chloroplast phenotype remains to be fully elucidated.Here, we demonstrate that a T-DNA insertion mutation in AtMinE1results in a severe inhibition of chloroplast division, producingmotile dots and short filaments of FtsZ. In AtMinE1 sense (overexpressor)plants, dividing chloroplasts possess either single or multipleFtsZ rings located at random intervals and showing constrictiondepth, mainly along the chloroplast polarity axis. The AtMinE1sense plants displayed equivalent chloroplast phenotypes toarc11, a loss-of-function mutant of AtMinD1 which forms replicatingmini-chloroplasts. Furthermore, a certain population of FtsZrings formed within developing chloroplasts failed to initiateor progress the membrane constriction of chloroplasts and consequentiallyto complete chloroplast fission in both AtMinE1 sense and arc11/atminD1plants. Our present data thus demonstrate that the chloroplastdivision site placement involves a balance between the opposingactivities of AtMinE1 and AtMinD1, which acts to prevent FtsZring formation anywhere outside of the mid-chloroplast. In addition,the imbalance caused by an AtMinE1 dominance causes multiple,non-synchronous division events at the single chloroplast level,as well as division arrest, which becomes apparent as the chloroplastsmature, in spite of the presence of FtsZ rings.     

Induction of serotonin accumulation by feeding of rice striped stem borer in rice leaves

Tryptophan (Trp)-related secondary metabolism has been implicated in the defense against pathogen infection and insect feeding in various gramineous species. Recently, we also reported that rice plant accumulated serotonin and tryptamine as well as their amide compounds coupled with phenolic acids in response to the infection by fungal pathogen. These compounds were likely to play an important role in the formation of physical barrier to the invading pathogens. To extend our study to elucidate the defensive role of Trp-derived secondary metabolism in gramineous plants, we examined in this study whether it is activated in response to herbivore attack as well. Third leaves of rice plant were fed on by third instar larvae of rice striped stem borer for 24 h or 48 h. The analysis of four Trp-derived metabolites including tryptamine, serotonin feruloyltryptamine (FerTry) and p-coumaroylserotonin (CouSer) by liquid chromatography coupled with tandem mass spectrometry revealed that their contents clearly increased in response to the larvae feeding. The respective amounts of tryptamine, serotonin, FerTry and CouSer in the larvae-fed leaves were 12-, 3.5-, 33- and 140-fold larger than those in control leaves 48 h after the start of feeding.Key words: rice, Oryza sativa, Gramineae, serotonin, secondary metabolism, rice striped stem borer, Chilo suppressalisPlants defend themselves from environmental stresses by utilizing secondary metabolism. One of major biological stresses that plants have to cope with is attack by herbivorous insects. In the interactions with herbivorous insects, various secondary metabolites that are derived from tryptophan (Trp) pathway have been shown to play defensive roles in plants including gramineous species. For example, benzoxazinone glucosides in wheat (Triticum aestivum), rye (Secale sereale) and maize (Zea mays) express toxic and antifeeding effects on herbivorous insects.^1,2 Benzoxazinones are biosynthesized from indole-3-glycerol phosphate, an intermediate of Trp synthesis.^3,4 Another example of those compounds is gramine in barley (Hordeum vulgare). Gramine is a Trp-rerived indole amine,⁵ and has been received attention in the resistance mainly against aphids on the basis of its toxicity and deterrence.⁶We recently found that Trp-derived secondary metabolism is also involved in defense responses of rice (Oryza sativa) leaves to infection by brown spot fungus (Bipolaris oryzae).⁷ The infection of the fungus activates Trp biosynthesis and accumulation of serotonin and of smaller amounts of tryptamine, feruloyltryptamine (FerTry) and p-coumaroylserotonin (CouSer). In addition, the enhancement of serotonin peroxidase activity and incorporation of serotonin in the cell walls were detected. Thus, it is very likely that that serotonin-derived materials deposit in cell walls after oxidative polymerization to constitute a part of physical defense system of rice, which may be reminiscent of the wound sloughing in animals. These findings prompted us to investigate whether Trp-related secondary metabolism is also involved in the defense of rice plant against the attack by insects, as in the cases of other gramineous plants mentioned above. While the response of plants to pathogenic infection is generally different from that to insect herbivory, Trp-derived secondary metabolites have occasionally been implicated in both responses.^8–10 Here, we report the results of our study to examine the effects of herbivory by rice striped stem borer (Chilo suppressalis) on the Trp derived secondary metabolism in rice leaves.Rice (cv. Nipponbare) leaves were incubated with larvae of C. suppressalis in a feeding tube assembled according to Oikawa et al.,⁸ Aerial parts of two 12-day-old rice seedlings were excised, and their cutting ends were immersed in distilled water in a vial. Three third instar larvae of C. suppressalis were put on the leaves, and the leaves with larvae were covered by a plastic tube. For comparison, the control leaves were wounded by razor blade at the start of the incubation. After incubation for 24 h or 48 h with 16/8 h LD cycle at 28°C, the leaves were extracted with 10 volumes of 80% methanol, and analyzed by liquid chromatography coupled with tandem mass spectrometry in multiple reaction monitoring mode.As shown in Figure 1, the contents of tryptamine and serotonin increased along with time in the larvae-fed leaves. The respective contents of tryptamine and serotonin in the leaves were 12- and 3.5-fold larger than those in control leaves 48 h after the start of feeding. The accumulation of FerTry and CouSer was also observed after larvae feeding with the contents being 33- and 140-fold larger than those in control leaves, respectively. Their contents, however, were approximately 10-fold smaller than the corresponding amines.Open in a separate windowFigure 1Accumulation of Trp derived metabolites in the leaves attacked by rice striped stem borer. Chemical structures of analyzed compounds (A). The contents of tryptamine (B), serotonin (B), FerTry (C) and CouSer (D) were determined by LC-MS/MS analysis. The third leaves of 12-d-old rice seedlings were fed on by rice striped stem borer (brack bars) or wounded by razor blade as control (white bars). After incubation, the leaves were extracted by 80% methanol. The contents of metabolites at time 0 are represented as gray bars.In the interaction of rice plant with B. oryzae, serotonin was shown to be incorporated into cell walls as a part of physical defense system.⁷ In an analogous way, modification of cell walls by serotonin might function in sealing the sites injured by insect feeding to protect the leaves from desiccation, and opportunistic and insect-mediated infection by microorganisms. Indeed, at the cutting edge of the leaves, the formation of brown materials was observed. In addition, since serotonin is a neurotransmitter of insects and tryptamine has been indicated to be a neuroactive substance, their accumulation might directly affect behavior and physiology of some insects. High concentrations of tryptamine have been shown to express anti-oviposition activity toward Bemisia tabaci¹¹ and anti-feeding activities toward Malacosoma disstria and Manduca sexta.¹²The low levels of serotonin, tryptamine and their amides in the control leaves suggest that these compounds are induced in response to some components produced during the interaction between the plant and the herbivore. In this relation, it has been shown that elicitors are present in the saliva of some herbivous insects, which induce volatile emission from the plant to attracts their natural enemies.^13,14 Induction of Trp-derived secondary metabolites by the herbivore attack may likely be a result of recognition of some insect-derived molecules by rice leaves, similarly to the induction of volatile emission.The induced accumulation of indole amines and their hydroxycinnamic acid amides in the rice leaves attacked by C. suppressalis suggests that a common signaling pathway might be involved in the responses to pathogen infection and insect feeding. However, the composition of induced compounds was different between the responses to the two biological stresses. The content of tryptamine in the larvae-fed leaves was comparable to that reported in the B. oryzae-infected leaves, whereas the amount of serotonin (approximately 35 nmol/gFW) was much smaller than that in the infected leaves (approximately 250 nmol/gFW). This characteristic was similar to the response of rice leaves to methyl jasmonate (MeJA), which also induced accumulation of these Trp-derived secondary metabolites.⁷ The strong activation of the conversion of tryptamine to serotonin may require infection-specific signals.The serotonin accumulation in rice appears to be similar to the accumulation of gramine in barley in several aspects. Gramine accumulation has been demonstrated to be induced by either infection by pathogens⁹ or infestation by the aphid Schizaphis graminum.¹⁰ In addition, the gene encoding N-methyltransferase that catalyzes the final reaction in the gramine biosynthetic pathway is upregulated by MeJA, suggesting gramine synthesis is at least partly under the control of jasmonate signaling pathway.^15,16 The inducible serotonin production may be an archetypal form of the biosynthesis of more complicated indole amine in barley.     

Comprehensive analysis of glycosyltransferases in eukaryotic genomes for structural and functional characterization of glycans

Glycosyltransferases comprise highly divergent groups of enzymes, which play a central role in the synthesis of complex glycans. Because the repertoire of glycosyltransferases in the genome determines the range of synthesizable glycans, and because the increasing amount of genome sequence data is now available, it is essential to examine these enzymes across organisms to explore possible structures and functions of the glycoconjugates. In this study, we systematically investigated 36 eukaryotic genomes and obtained 3426 glycosyltransferase homologs for biosynthesis of major glycans, classified into 53 families based on sequence similarity. The families were further grouped into six functional categories based on the biosynthetic pathways, which revealed characteristic patterns among organism groups in the degree of conservation and in the number of paralogs. The results also revealed a strong correlation between the number of glycosyltransferases and the number of coding genes in each genome. We then predicted the ability to synthesize major glycan structures including N-glycan precursors and GPI-anchors in each organism from the combination of the glycosyltransferase families. This indicates that not only parasitic protists but also some algae are likely to synthesize smaller structures than the structures known to be conserved among a wide range of eukaryotes. Finally we discuss the functions of two large families, sialyltransferases and β4-glycosyltransferases, by performing finer classifications into subfamilies. Our findings suggest that universality and diversity of glycans originate from two types of evolution of glycosyltransferase families, namely conserved families with few paralogs and diverged families with many paralogs.     

Therapeutic Strategy for Ischemic Stroke

Possible strategies for treating ischemic stroke include: (1) Neuroprotection: preventing damaged neurons from undergoing apoptosis in the acute phase of cerebral ischemia; (2) Stem cell therapy: the repair of broken neuronal networks with newly born neurons in the chronic phase of cerebral ischemia. Firstly, we studied the neuroprotective effect of a calcium channel blocker, azelnidipine, or a by-product of heme degradation, biliverdin, in the ischemic brain. These results revealed both azelnidipine and biliverdin had a neuroprotective effect in the ischemic brain through their anti-oxidative property. Secondly, we investigated the role of granulocyte colony-stimulating factor (G-CSF) by administering G-CSF to rats after cerebral ischemia and found G-CSF plays a critical role in neuroprotection. Lastly, we developed a restorative stroke therapy with a bio-affinitive scaffold, which is able to provide an appropriate environment for newly born neurons. In the future, we will combine these strategies to develop more effective therapies for treatment of strokes. Special issue article in honor of Dr. Akitane Mori.     

Absolute configuration of (+)-pinoresinol 4-O-[6″-O-galloyl]-β-d-glucopyranoside, macarangiosides E, and F isolated from the leaves of Macaranga tanarius

A lignan glucoside, (+)-pinoresinol 4-O-[6″-O-galloyl]-β-d-glucopyranoside (1), and two megastigmane glucosides, named macarangiosides E and F (2, 3), together with 15 known compounds (4–18) were isolated from leaves of Macaranga tanarius (L.) Müll.-Arg. (Euphorbiaceae). Their structures were elucidated by spectroscopic and chemical analyses. In addition, the absolute stereochemistry of macarangiosides B and C isolated previously from the same plant was also determined for the first time. Compounds 1 and 2 were galloylated on glucose and possessed potent DPPH radical-scavenging activity.     

Association between antibody response against cytomegalovirus strain-specific glycoprotein H epitopes and HLA-DR

The gH of CMV is a major target for strain-specific neutralizing antibodies. To verify whether there is a correlation between HLA-DR type and strain-specific antibodies, antibodies against CMV gH in potential donors and recipients for renal transplantation were investigated. Among 471 subjects, 404 (86%) showed reactivity to CMV gH, but no antibodies against gH were detected in 67 (14%) subjects. The positive rates were over 80% in most HLA subpopulations. Fewer subjects with HLA-DR10 and DR11 had antibodies to CMV gH than did those without HLA-DR10 and DR11. HLA-DR10 and DR11 may be associated with fewer/non-responders for strain-specific neutralizing antibodies.     

Cytoprotective effects of the lipoidic‐liquiform pro‐vitamin C tetra‐isopalmitoyl‐ascorbate (VC‐IP) against ultraviolet‐A ray‐induced injuries in human skin cells together with collagen retention,MMP inhibition and p53 gene repression

Irradiation with ultraviolet‐A (UVA) ray at doses of 20–100 J/cm² diminished the cell viability of human keratinocytes HaCaT and human melanoma cells HMV‐II, both of which were protected by pre‐irradiational administration with the ascorbic acid (Asc) derivative, VC‐IP (2,3,5,6‐O‐tetra‐2′‐hexyldecanoyl‐L‐ascorbic acid; vitamin C‐isopalmityl tetraester), which is the first lipoidic‐liquiform pro‐vitamin C by itself that is materialized by esterization of all four intramolecular hydroxyl groups of an Asc molecule with branched chain fatty groups, resulting in molecular fluidity higher than that of the corresponding straight chains. Irradiation with UVA to HaCaT keratinocytes was shown to cause the formation of 8‐hydroxydeoxyguanosine (8‐OHdG), translocation of phosphatidylserine in the inner layer into the outer layer of cell membrane, and lowering of a mitochondrial membrane potential, all of which were repressed by pre‐irradiational administration with VC‐IP. Expression of p53 gene, another hallmark of UV‐induced DNA damages, was promoted by UVA irradiation to the keratinocytes but also repressed by VC‐IP. Administration with VC‐IP of 10–50 µM to human fibroblasts NHDF achieved the enhancement of collagen synthesis, repression of matrix metalloprotease‐2/9 activity, and increasing of intracellular Asc contents more markedly than that with Asc itself of the same concentrations. Thus UVA‐induced diverse harmful effects could be prevented by VC‐IP, which was suggested to ensue intrinsically from the persistent enrichment of intracellular Asc, through esterolytic conversion of VC‐IP to a free‐form Asc molecule, resulting in relief to UVA‐caused oxidative stress. J. Cell. Biochem. 106: 589–598, 2009. © 2009 Wiley‐Liss, Inc.