Asian flush is a potential protective factor against COVID-19: a web-based retrospective survey in Japan.

BACKGROUND: Coronavirus disease 2019 (COVID-19), first reported in December 2019, spread worldwide in a short period, resulting in numerous cases and associated deaths; however, the toll was relatively low in East Asia. A genetic polymorphism unique to East Asians, Aldehyde dehydrogenase 2 rs671, has been reported to confer protection against infections. METHOD: We retrospectively investigated the association between the surrogate marker of the rs671 variant, the skin flushing phenomenon after alcohol consumption, and the timing of COVID-19 incidence using a web-based survey tool to test any protective effects of rs671 against COVID-19. RESULTS: A total of 807 valid responses were received from 362 non-flushers and 445 flushers. During the 42 months, from 12/1/2019 to 5/31/2023, 40.6% of non-flushers and 35.7% of flushers experienced COVID-19. Flushers tended to have a later onset (Spearman's partial rank correlation test, p = 0.057, adjusted for sex and age). Similarly, 2.5% of non-flushers and 0.5% of flushers were hospitalized because of COVID-19. Survival analysis estimated lower risks of COVID-19 and associated hospitalization among flushers (p = 0.03 and <0.01, respectively; generalized Wilcoxon test). With the Cox proportional hazards model covering 21 months till 8/31/2021, when approximately half of the Japanese population had received two doses of COVID-19 vaccine, the hazard ratio (95% confidence interval) of COVID-19 incidence was estimated to be 0.21 (0.10-0.46) for flusher versus non-flusher, with adjustment for sex, age, steroid use, and area of residence. CONCLUSIONS: Our study suggests an association between the flushing phenomenon after drinking and a decreased risk of COVID-19 morbidity and hospitalization, suggesting that the rs671 variant is a protective factor. This study provides valuable information for infection control and helps understand the unique constitutional diversity of East Asians.

In Vivo Phosphorylation: Development of Specific Antibodies to Detect the Phosphorylated PEPC Isoform for the C4 Photosynthesis in Zea mays.

Phosphoenolpyruvate carboxylases (PEPCs), mostly known as the enzymes responsible for the initial CO2 fixation during C4 photosynthesis, are regulated by reversible phosphorylation in vascular plants. The phosphorylation site on a PEPC molecule is conserved not only among isoforms but also across plant species. An anti-phosphopeptide antibody is a common and powerful tool for detecting phosphorylated target proteins with high specificity. We generated two antibodies, one against a peptide containing a phosphoserine (phosphopeptide) and the other against a peptide containing a phosphoserine mimetic, (S)-2-amino-4-phosphonobutyric acid (phosphonopeptide). The amino acid sequence of the peptide was taken from the site around the phosphorylation site near the N-terminal region of the maize C4-isoform of PEPC. The former antibodies detected almost specifically the phosphorylated C4-isoform of PEPC, whereas the latter antibodies had a broader specificity for the phosphorylated PEPC in various plant species. The following procedures are described herein: (1) preparation of the phosphopeptide and phosphonopeptide; (2) preparation and purification of rabbit antibodies; (3) preparation of cell extracts from leaves for analyses of PEPC phosphorylation with antibodies; and (4) characterization of the obtained antibodies. Finally, (5) two cases involving the application of these antibodies are presented.

A plastidial sodium-dependent pyruvate transporter.

Pyruvate serves as a metabolic precursor for many plastid-localized biosynthetic pathways, such as those for fatty acids, terpenoids and branched-chain amino acids. In spite of the importance of pyruvate uptake into plastids (organelles within cells of plants and algae), the molecular mechanisms of this uptake have not yet been explored. This is mainly because pyruvate is a relatively small compound that is able to passively permeate lipid bilayers, which precludes accurate measurement of pyruvate transport activity in reconstituted liposomes. Using differential transcriptome analyses of C(3) and C(4) plants of the genera Flaveria and Cleome, here we have identified a novel gene that is abundant in C(4) species, named BASS2 (BILE ACID:SODIUM SYMPORTER FAMILY PROTEIN 2). The BASS2 protein is localized at the chloroplast envelope membrane, and is highly abundant in C(4) plants that have the sodium-dependent pyruvate transporter. Recombinant BASS2 shows sodium-dependent pyruvate uptake activity. Sodium influx is balanced by a sodium:proton antiporter (NHD1), which was mimicked in recombinant Escherichia coli cells expressing both BASS2 and NHD1. Arabidopsis thaliana bass2 mutants lack pyruvate uptake into chloroplasts, which affects plastid-localized isopentenyl diphosphate synthesis, as evidenced by increased sensitivity of such mutants to mevastatin, an inhibitor of cytosolic isopentenyl diphosphate biosynthesis. We thus provide molecular evidence for a sodium-coupled metabolite transporter in plastid envelopes. Orthologues of BASS2 can be detected in all the genomes of land plants that have been characterized so far, thus indicating the widespread importance of sodium-coupled pyruvate import into plastids.

Interplay of light and temperature during the in planta modulation of C4 phosphoenolpyruvate carboxylase from the leaves of Amaranthus hypochondriacus L.: diurnal and seasonal effects manifested at molecular levels.

The interactive effects of light and temperature on C(4) phosphoenolpyruvate carboxylase (PEPC) were examined both in vivo and in situ using the leaves of Amaranthus hypochondriacus collected at different times during a day and in each month during the year. The maximum activity of PEPC, least inhibition by malate, and highest activation by glucose-6-phosphate were at 15.00 h during a typical day, in all the months. This peak was preceded by maximum ambient light but coincided with high temperature in the field. The highest magnitude in such responses was in the summer (e.g. May) and least in the winter (e.g. December). Light appeared to dominate in modulating the PEPC catalytic activity, whereas temperature had a strong influence on the regulatory properties, suggesting interesting molecular interactions. The molecular mechanisms involved in such interactive effects were determined by examining the PEPC protein/phosphorylation/mRNA levels. A marked diurnal rhythm could be seen in the PEPC protein levels and phosphorylation status during May (summer month). In contrast, only the phosphorylation status increased during the day in December (winter month). The mRNA peaks were not as strong as those of phosphorylation. Thus, the phosphorylation status and the protein levels of PEPC were crucial in modulating the daily and seasonal patterns in C(4) leaves in situ. This is the first detailed study on the diurnal as well as seasonal patterns in PEPC activity, its regulatory properties, protein levels, phosphorylation status, and mRNA levels, in relation to light and temperature intensities in the field.

Overexpression of an HPS/PHI fusion enzyme from Mycobacterium gastri in chloroplasts of geranium enhances its ability to assimilate and phytoremediate formaldehyde.

3-Hexulose-6-phosphate synthase (HPS) and 6-phosphate-3-hexuloisomerase (PHI) are two key enzymes in the formaldehyde (HCHO) assimilation pathway in methylotrophs. The HPS/PHI fusion protein, encoded by the chimeric gene of hps and phi from Mycobacterium gastri MB19, possesses both HPS and PHI activities in an Escherichia coli transformant. Overexpression of the fusion protein in chloroplasts of geranium (Pelargonium sp. Frensham) created a photosynthetic HCHO assimilation pathway according to (13)C-NMR analysis. The transgenic plants exhibited an enhanced ability in HCHO-uptake and [(14)C]HCHO-assimilation. Moreover, the transgenic plants showed greater HCHO-resistance and stronger capacity in purification of the HCHO-polluted air. Therefore, the use of the single chimeric gene may not only greatly simplify the transformation procedure but also improve the efficiency of phytoremediating HCHO in ornamental plants.

Assimilation of formaldehyde in transgenic plants due to the introduction of the bacterial ribulose monophosphate pathway genes.

Formaldehyde (HCHO) is an air pollutant suspected of being carcinogenic and a cause of sick-house syndrome. Microorganisms called methylotrophs, which can utilize reduced C(1) compounds such as methane and methanol, fix and assimilate HCHO, whereas most plants are unable to assimilate HCHO directly. We found that a bacterial formaldehyde-fixing pathway (ribulose monophosphate pathway) can be integrated as a bypass to the Calvin-Benson cycle in transgenic Arabidopsis thaliana and tobacco by genetic engineering. These plants showed enhanced tolerance to HCHO and enhanced capacity to eliminate gaseous HCHO by fixing it as a sugar phosphate. Our results provide a novel strategy for phytoremediation of HCHO pollution, and also represent the first step toward the production of plants that can assimilate natural gas-derived C(1) compounds.

Maize C4-form phosphoenolpyruvate carboxylase engineered to be functional in C3 plants: mutations for diminished sensitivity to feedback inhibitors and for increased substrate affinity.

Introducing a C(4)-like pathway into C(3) plants is one of the proposed strategies for the enhancement of photosynthetic productivity. For this purpose it is necessary to provide each component enzyme that exerts strong activity in the targeted C(3) plants. Here, a maize C(4)-form phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) was engineered for its regulatory and catalytic properties so as to be functional in the cells of C(3) plants. Firstly, amino acid residues Lys-835 and Arg-894 of maize PEPC, which correspond to Lys-773 and Arg-832 of Escherichia coli PEPC, respectively, were replaced by Gly, since they had been shown to be involved in the binding of allosteric inhibitors, malate or aspartate, by our X-ray crystallographic analysis of E. coli PEPC. The resulting mutant enzymes were active but their sensitivities to the inhibitors were greatly diminished. Secondly, a Ser residue (S780) characteristically conserved in all C(4)-form PEPC was replaced by Ala conserved in C(3)- and root-form PEPCs to decrease the half-maximal concentration (S(0.5)) of PEP. The double mutant enzyme (S780A/K835G) showed diminished sensitivity to malate and decreased S(0.5)(PEP) with equal maximal catalytic activity (V(m)) to the wild-type PEPC, which will be quite useful as a component of the C(4)-like pathway to be introduced into C(3) plants.

Transcriptome profiling of Lotus japonicus roots during arbuscular mycorrhiza development and comparison with that of nodulation.

To better understand the molecular responses of plants to arbuscular mycorrhizal (AM) fungi, we analyzed the differential gene expression patterns of Lotus japonicus, a model legume, with the aid of a large-scale cDNA macroarray. Experiments were carried out considering the effects of contaminating microorganisms in the soil inoculants. When the colonization by AM fungi, i.e. Glomus mosseae and Gigaspora margarita, was well established, four cysteine protease genes were induced. In situ hybridization revealed that these cysteine protease genes were specifically expressed in arbuscule-containing inner cortical cells of AM roots. On the other hand, phenylpropanoid biosynthesis-related genes for phenylalanine ammonia-lyase (PAL), chalcone synthase, etc. were repressed in the later stage, although they were moderately up-regulated on the initial association with the AM fungus. Real-time RT-PCR experiments supported the array experiments. To further confirm the characteristic expression, a PAL promoter was fused with a reporter gene and introduced into L. japonicus, and then the transformants were grown with a commercial inoculum of G. mosseae. The reporter activity was augmented throughout the roots due to the presence of contaminating microorganisms in the inoculum. Interestingly, G. mosseae only colonized where the reporter activity was low. Comparison of the transcriptome profiles of AM roots and nitrogen-fixing root nodules formed with Mesorhizobium loti indicated that the PAL genes and other phenylpropanoid biosynthesis-related genes were similarly repressed in the two organs.

Phosphorylation of phosphoenolpyruvate carboxylase is not essential for high photosynthetic rates in the C4 species Flaveria bidentis.

Phosphoenolpyruvate carboxylase (PEPC; EC4.1.1.31) plays a key role during C(4) photosynthesis. The enzyme is activated by metabolites such as glucose-6-phosphate and inhibited by malate. This metabolite sensitivity is modulated by the reversible phosphorylation of a conserved serine residue near the N terminus in response to light. The phosphorylation of PEPC is modulated by a protein kinase specific to PEPC (PEPC-PK). To explore the role PEPC-PK plays in the regulation of C(4) photosynthetic CO(2) fixation, we have transformed Flaveria bidentis (a C(4) dicot) with antisense or RNA interference constructs targeted at the mRNA of this PEPC-PK. We generated several independent transgenic lines where PEPC is not phosphorylated in the light, demonstrating that this PEPC-PK is essential for the phosphorylation of PEPC in vivo. Malate sensitivity of PEPC extracted from these transgenic lines in the light was similar to the malate sensitivity of PEPC extracted from darkened wild-type leaves but greater than the malate sensitivity observed in PEPC extracted from wild-type leaves in the light, confirming the link between PEPC phosphorylation and the degree of malate inhibition. There were, however, no differences in the CO(2) and light response of CO(2) assimilation rates between wild-type plants and transgenic plants with low PEPC phosphorylation, showing that phosphorylation of PEPC in the light is not essential for efficient C(4) photosynthesis for plants grown under standard glasshouse conditions. This raises the intriguing question of what role this complexly regulated reversible phosphorylation of PEPC plays in C(4) photosynthesis.

Temporary expression of the TAF10 gene and its requirement for normal development of Arabidopsis thaliana.

TAF10 is one of the TATA box-binding protein (TBP)-associated factors (TAFs) which constitute a TFIID with a TBP. Initially most TAFs were thought to be necessary for accurate transcription initiation from a broad group of core promoters. However, it was recently revealed that several TAFs are expressed in limited tissues during animal embryogenesis, and are indispensable for normal development of the tissues. They are called 'selective' TAFs. In plants, however, little is known as to these 'selective' TAFs and their function. Here we isolated the Arabidopsis thaliana TAF10 gene (atTAF10), which is a single gene closely related to the TAF10 genes of other organisms. atTAF10 was expressed transiently during the development of several organs such as lateral roots, rosette leaves and most floral organs. Such an expression pattern was clearly distinct from that of Arabidopsis Rpb1, which encodes a component of RNA polymerase II, suggesting that atTAF10 functions in not only general transcription but also the selective expression of a subset of genes. In a knockdown mutant of atTAF10, we observed several abnormal phenotypes involved in meristem activity and leaf development, suggesting that atTAF10 is concerned in pleiotropic, but selected morphological events in Arabidopsis. These results clearly demonstrate that TAF10 is a 'selective' TAF in plants, providing a new insight into the function of TAFs in plants.

Purification capability of tobacco transformed with enzymes from a methylotrophic bacterium for formaldehyde.

Plants have the ability to remediate environmental pollution. Especially, they have a high purification capability for airpollution. We have measured the purification characteristics of foliage plants for indoor airpollutants--for example, formaldehyde (HCHO), toluene, and xylene--using a tin oxide gas sensor. HCHO is an important intermediate for biological fixation of C1 compounds in methylotrophs. The ribulose monophosphate pathway of HCHO fixation is inherent in many methylotrophic bacteria, which can grow on Cl compounds. Two genes for the key enzymes, HPS and PHI, from the methylotrophic bacterium Mycobacterium gastri MB19 were introduced into tobacco. In this article, the HCHO-removal characteristic of the transformant was examined by using the gas sensor in order to evaluate quantitatively. The purification characteristics of the transformant for toluene, xylene, and styrene were also measured. The results confirmed an increase of 20% in the HCHO-removal capability. The differences of the purification capabilities for toluene, xylene, and styrene were not recognized.

A novel mechanism of allosteric regulation of archaeal phosphoenolpyruvate carboxylase: a combined approach to structure-based alignment and model assessment.

Phosphoenolpyruvate carboxylase (PEPC) catalyzes the irreversible carboxylation of phosphoenolpyruvate (PEP) and plays a crucial role in fixing atmospheric CO(2) in C(4) and CAM plants. The enzyme is widespread in plants and bacteria and mostly regulated allosterically by both positive and negative effectors. Archaeal PEPCs (A-PEPCs) have unique characteristics in allosteric regulation and molecular mass, distinct from their bacterial and eukaryote homologues, and their amino acid sequences have become available only recently. In this paper, we generated a structure-based alignment of archaeal, bacterial and eukaryote PEPCs and built comparative models using a combination of fold recognition, sequence and structural analysis tools. Our comparative modeling analysis identified A-PEPC-specific strong interactions between the two loops involved in both allostery and catalysis, which explained why A-PEPC is not influenced by any allosteric activators. We also found that the side-chain located three residues before the C-terminus appears to play a key role in determining the sensitivity to allosteric inhibitors. In addition to these unique features, we revealed how archaeal, bacterial and eukaryote PEPCs would share a common catalytic mechanism and adopt a similar mode of tetramer formation, despite their divergent sequences. Our novel observations will help design more efficient molecules for ecological and industrial use.

Knockdown of an arbuscular mycorrhiza-inducible phosphate transporter gene of Lotus japonicus suppresses mutualistic symbiosis.

cDNA for a major arbuscular mycorrhiza (AM)-inducible phosphate (Pi) transporter of Lotus japonicus, LjPT3, was isolated from Glomus mosseae-colonized roots. The LjPT3 transcript was expressed in arbuscule-containing cells of the inner cortex. The transport activity of the gene product was confirmed by the complementation of a yeast mutant that lacks high-affinity Pi transporters. In contrast to most AM-inducible Pi transporters thus far reported, LjPT3 has an amino acid sequence that has much in common with those of other members of the Pht1 family of plant Pi transporters, such as StPT3 of potato. To understand better the physiological role of this AM-inducible Pi transporter, knockdown transformants of the gene were prepared through hairy root transformation and RNA interference. Under Pi-limiting conditions, the transformants showed a reduction of Pi uptake via AM and growth retardation. The transformants also exhibited a decrease in G. mosseae arbuscules. Additionally, when Mesorhizobium loti was inoculated into the knockdown transformants in combination with G. mosseae, necrotic root nodules were observed. Based on these findings, we consider that the genetically engineered host plants had monitored insufficient Pi uptake via AM or low expression of LjPT3, excluding the existing fungi and rhizobia and/or preventing further development of the fungal and nodule structures.

Phosphoenolpyruvate carboxylase plays a crucial role in limiting nitrogen fixation in Lotus japonicus nodules.

Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) is believed to play a significant role in supporting nitrogen fixation via anaplerotic CO2 fixation for recycling carbon in nodules. Using the antisense technique, we decreased the expression levels of the nodule-enhanced PEPC gene (Ljpepc1) in a determinate legume plant (Lotus japonicus) in order to look at the influence of the symbiotic phenotype and biochemical parameters. Three independent transgenic L. japonicus plants (designated as Asppc1, Asppc2 and Asppc3) were prepared using a Ljpepc1 DNA fragment which is under the control of the cauliflower mosaic virus 35S promoter. Extensive suppression of the Ljpepc1 transcript in nodules of Asppc plants (T3 homologous plants) was confirmed by RNA gel blot, Western blot and enzyme activity assays. In nodules of Asppc plants, PEPC activity was reduced to about 10% of that of non-transformants and the plants showed typical nitrogen-deficient symptoms without a supply of nitrogen nutrient, and returned to normal growth when nitrate was supplied at 2.5 mM. The acetylene reduction activity per fresh weight of nodules of these Asppc plants decreased by 29% at 35 dai (days after infection). Various enzyme activities and metabolite levels were surveyed using Asppc plants at 35 dai. Significant reduction of sucrose synthase and asparagine aminotransferase activities was observed in Asppc nodules. In addition, sucrose, succinate, asparagine, aspartate and glutamate contents also decreased in Asppc nodules. The data are discussed in terms of a role for PEPC in the carbon/nitrogen metabolic flux in nodules.

Characterization of the Lotus japonicus symbiotic mutant lot1 that shows a reduced nodule number and distorted trichomes.

We isolated a recessive symbiotic mutant of Lotus japonicus that defines a genetic locus, LOT1 (for low nodulation and trichome distortion). The nodule number per plant of the mutant was about one-fifth of that of the wild type. The lot1 mutant showed a moderate dwarf phenotype and distorted trichomes, but its root hairs showed no apparent differences to those of the wild type. Infection thread formation after inoculation of Mesorhizobium loti was repressed in lot1 compared to that in the wild type. The nodule primordia of lot1 did not result in any aborted nodule-like structure, all nodules becoming mature and exhibiting high nitrogen fixation activity. The mutant was normally colonized by mycorrhizal fungi. lot1 also showed higher sensitivity to nitrate than the wild type. The grown-up seedlings of lot1 were insensitive to any ethylene treatments with regard to nodulation, although the mutant showed normal triple response on germination. It is conceivable that a nodulation-specific ethylene signaling pathway is constitutively activated in the mutant. Grafting experiments with lot1 and wild-type seedlings suggested that the root genotype mainly determines the low nodulation phenotype of the mutant, while the trichome distortion is regulated by the shoot genotype. Grafting of har1-4 shoots to lot1 roots resulted in an intermediate nodule number, i.e. more than that of lot1 and less than that of har1-4. Putative double mutants of lot1 and har1 also showed intermediate nodulation. Thus, it was indicated that LOT1 is involved in a distinct signal transduction pathway independent of HAR1.

The ubiquitin-proteasome pathway is involved in rapid degradation of phosphoenolpyruvate carboxylase kinase for C4 photosynthesis.

In C4 photosynthesis, phosphoenolpyruvate carboxylase (PEPC) is the enzyme responsible for catalyzing the primary fixation of atmospheric CO2. The activity of PEPC is regulated diurnally by reversible phosphorylation. PEPC kinase (PEPCk), a protein kinase involved in this phosphorylation, is highly specific for PEPC and consists of only the core domain of protein kinase. Owing to its extremely low abundance in cells, analysis of its regulatory mechanism at the protein level has been difficult. Here we employed a transient expression system using maize mesophyll protoplasts. The PEPCk protein with a FLAG tag could be expressed correctly and detected with high sensitivity. Rapid degradation of PEPCk protein was confirmed and shown to be blocked by MG132, a 26S proteasome inhibitor. Furthermore, MG132 enhanced accumulation of PEPCk with increased molecular sizes at about 8 kDa intervals. Using anti-ubiquitin antibody, this increase was shown to be due to ubiquitination. This is the first report to show the involvement of the ubiquitin-proteasome pathway in PEPCk turnover. The occurrence of PEPCks with higher molecular sizes, which was noted previously with cell extracts from various plants, was also suggested to be due to ubiquitination of native PEPCk.

Abundant expression in vascular tissue of plant TAF10, an orthologous gene for TATA box-binding protein-associated factor 10, in Flaveria trinervia and abnormal morphology of Arabidopsis thaliana transformants on its overexpression.

TAF10 is one of the TATA box-binding protein-associated factors (TAFs), which constitute the TFIID complex. We isolated a plant TAF10 ortholog from a Flaveria trinervia cDNA library, and named it ftTAF10. The ftTAF10 polypeptide contains a histone-fold motif, which is highly conserved among the TAF10s of other organisms. A transiently expressed green fluorescent protein (GFP) fusion protein was translocated into the nuclei of onion epidermal cells, suggesting that the ftTAF10 functions in nuclei. The transcript level was higher in stems and roots than in leaves, and in situ hybridization of F. trinervia seedlings revealed that the ftTAF10 transcript is accumulated abundantly in vascular tissues of hypocotyls, in the central cylinder of roots, and slightly in bundle sheath cells of leaves. Overexpression of ftTAF10 in Arabidopsis under the cauliflower mosaic virus 35S promoter caused two kinds of abnormal morphology, limitation of the indeterminate inflorescence and production of deformed leaves. These results indicate the possibility that ftTAF10 is a plant 'selective TAF' involved in the expression of a subset of vascular abundant genes, and that its appropriate gene expression is necessary for normal development.

Maize phosphoenolpyruvate carboxylase. Mutations at the putative binding site for glucose 6-phosphate caused desensitization and abolished responsiveness to regulatory phosphorylation.

Phosphoenolpyruvate carboxylases (PEPC, EC 4.1.1.31) from higher plants are regulated by both allosteric effects and reversible phosphorylation. Previous x-ray crystallographic analysis of Zea mays PEPC has revealed a binding site for sulfate ion, speculated to be the site for an allosteric activator, glucose 6-phosphate (Glc-6-P) (Matsumura, H., Xie, Y., Shirakata, S., Inoue, T., Yoshinaga, T., Ueno, Y., Izui, K., and Kai, Y. (2002) Structure (Lond.) 10, 1721-1730). Because kinetic experiments have also supported this notion, each of the four basic residues (Arg-183, -184, -231, and -372' on the adjacent subunit) located at or near the binding site was replaced by Gln, and the kinetic properties of recombinant mutant enzymes were investigated. Complete desensitization to Glc-6-P was observed for R183Q, R184Q, R183Q/R184Q (double mutant), and R372Q, as was a marked decrease in the sensitivity for R231Q. The heterotropic effect of Glc-6-P on an allosteric inhibitor, l-malate, was also abolished, but sensitivity to Gly, another allosteric activator of monocot PEPC, was essentially not affected, suggesting the distinctness of their binding sites. Considering the kinetic and structural data, Arg-183 and Arg-231 were suggested to be involved directly in the binding with phosphate group of Glc-6-P, and the residues Arg-184 and Arg-372 were thought to be involved in making up the site for Glc-6-P and/or in the transmission of an allosteric regulatory signal. Most unexpectedly, the mutant enzymes had almost lost responsiveness to regulatory phosphorylation at Ser-15. An apparent lack of kinetic competition between the phosphate groups of Glc-6-P and of phospho-Ser at 15 suggested the distinctness of their binding sites. The possible roles of these Arg residues are discussed.

Cloning and expression analysis of a MAPKKK gene and a novel nodulin gene of Lotus japonicus.

We isolated a cDNA encoding mitogen-activated protein kinase kinase kinase alpha, designated LjM3Kalpha, from Lotus japonicus, a model legume. The gene was expressed constitutively in roots, root nodules, and shoots. We also identified a novel nodulin gene, LjNUF, that shows specific expression in nodules. LjNUF resembles the C-terminal half of a hypothetical protein (pir//D85436), the N-terminal half of which is similar to a portion of mitogen-activated protein kinase kinase kinase gamma. Although LjNUF was predicted to be a secreted protein, its function remains to be clarified.

Overexpression of a cyanobacterial phosphoenolpyruvate carboxylase with diminished sensitivity to feedback inhibition in Arabidopsis changes amino acid metabolism.

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Synechococcus vulcanus (SvPEPC) is a unique enzyme, being almost insensitive to feedback inhibition at neutral pH. In order to assess its usefulness in metabolic engineering of plants, SvPEPC was expressed in Arabidopsis thaliana (L.) Heynh. under the control of the cauliflower mosaic virus 35S promoter. About one-third of the transformants of the T1 generation showed severe visible phenotypes such as leaf bleaching and were infertile when grown on soil. However, no such phenotype was observed with Arabidopsis transformed with Zea mays L. PEPC (ZmPEPC) for C4 photosynthesis, which is normally sensitive to a feedback inhibitor, L-malate. For the SvPEPC transformants of the T2 generation, which had been derived from fertile T1 transformants, three kinds of phenotype were observed when plants were grown on an agar medium containing sucrose: Type-I plants showed poor growth and a block in true leaf development; Type-II plants produced a few true leaves, which were partially bleached; Type-III plants were apparently normal. In Type-I plants, total PEPC activity was increased about 2-fold over the control plant but there was no such increase in Type-III plants. The phenotypes of Type-I plants were rescued when the sucrose-containing agar medium was supplemented with aromatic amino acids. Measurement of the free amino acid content in whole seedlings of Type-I transformants revealed that the levels of the aromatic amino acids Phe and Tyr were lowered significantly as compared with the control plants. In contrast, the levels of several amino acids of the aspartic and glutamic families, such as Asn, Gln and Arg, were markedly enhanced (4- to 8-fold per plant fresh weight). However, when the medium was supplemented with aromatic amino acids, the levels of Asn, Gln, and Arg decreased to levels slightly higher than those of control plants, accompanied by growth recovery. Taken together, it can be envisaged that SvPEPC is capable of efficiently exerting its activity in the plant cell environment so as to cause imbalance between aromatic and non-aromatic amino acid syntheses. The growth inhibition of Type-I plants was presumed to be primarily due to a decreased availability of phosphoenolpyruvate, one of the precursors for the shikimate pathway for the synthesis of aromatic amino acids and phenylpropanoids. The possible usefulness of SvPEPC as one of the key components for installing the C4-like pathway is proposed.