An amino acid transporter-like protein (OsATL15) facilitates the systematic distribution of thiamethoxam in rice for controlling the brown planthopper

Characterization and genetic engineering of plant transporters involved in the pesticide uptake and translocation facilitate pesticide relocation to the tissue where the pests feed, thus improving the bioavailability of the agrichemicals. We aimed to identify thiamethoxam (THX) transporters in rice and modify their expression for better brown planthopper (BPH) control with less pesticide application. A yeast library expressing 1385 rice transporters was screened, leading to the identification of an amino acid transporter-like (ATL) gene, namely OsATL15, which facilitates THX uptake in both yeast cells and rice seedlings. In contrast to a decrease in THX content in osatl15 knockout mutants, ectopic expression of OsATL15 under the control of the CaMV 35S promoter or a vascular-bundle-specific promoter gdcsPpro significantly increased THX accumulation in rice plants, thus further enhancing the THX efficacy against BPH. OsATL15 was localized in rice cell membrane and abundant in the root transverse sections, vascular bundles of leaf blade, and stem longitudinal sections, but not in hull and brown rice at filling stages. Our study shows that OsATL15 plays an essential role in THX uptake and its systemic distribution in rice. OsATL15 could be valuable in achieving precise pest control by biotechnology approaches.

ATP binding cassette proteins ABCG37 and ABCG33 function as potassium-independent cesium uptake carriers in Arabidopsis roots

Radiocesium accumulated in the soil by nuclear accidents is a major environmental concern. The transport process of cesium (Cs⁺) is tightly linked to the indispensable plant nutrient potassium (K⁺) as they both belong to the group I alkali metals with similar chemical properties. Most of the transporters that had been characterized to date as Cs⁺ transporters are directly or indirectly linked to K⁺. Using a combinatorial approach of physiology, genetics, cell biology, and root uptake assay, here we identified two ATP-binding cassette (ABC) proteins, ABCG37 and ABCG33, as facilitators of Cs⁺ influx. A gain-of-function mutant of ABCG37 (abcg37-1) showed increased sensitivity to Cs⁺-induced root growth inhibition, while the double knockout mutant of ABCG33 and ABCG37 (abcg33-1abcg37-2) showed resistance, whereas the single loss-of-function mutants of ABCG33 and ABCG37 did not show any alteration in Cs⁺ response. In planta short-term radioactive Cs⁺-uptake assay along with growth and uptake assays in a heterologous system confirmed ABCG33 and ABCG37 as Cs⁺-uptake carriers. Potassium response and content were unaffected in the double-mutant background and yeast cells lacking potassium-uptake carriers transformed with ABCG33 and ABCG37 failed to grow in the absence of K⁺, confirming that Cs⁺ uptake by ABCG33 and ABCG37 is independent of K⁺. Collectively, this work identified two ABC proteins as new Cs⁺-influx carriers that act redundantly and independent of the K⁺-uptake pathway.

Influence of low O2 and high CO2 environment on changes in metabolite concentrations in harvested vegetable soybeans

Influence of atmosphere and storage period on the physicochemical and biological properties of harvested vegetable soybeans stored for 10 d at 25 °C was investigated. Storing vegetable soybeans under modified atmosphere (low O2 and high CO2), was more effective in maintaining its green color and mass than storing them under normoxia. Principal component 1 (PC1; contribution rate: 25%) was related to the atmospheres, whereas PC2 (contribution rate: 19%) was related to storage period. Cluster analysis showed that some types of sugars decreased, whereas some types of organic and amino acids increased with deterioration. Alanine, an indicator of low O2 stress, was maintained for 3 d under modified atmospheres, whereas alanine significantly decreased under normoxia. The concentrations of inositol and niacinamide (functional ingredients) under the modified atmospheres were significantly higher than those under normoxia. Thus, storage under modified atmospheres was effective in maintaining freshness and increasing the nutritional content of vegetable soybeans.

Effect of the storage atmosphere on metabolomics of harvested tomatoes (Solanum lycopersicum L.)

Harvested tomatoes were stored under atmospheres that were normoxic, anoxic, or modified (altered O2 and CO2 concentrations). Each atmosphere was created by storing the tomatoes at 25°C for up to 8 days in different kinds of pouches. During storage, metabolites of the tomatoes were measured using metabolomics. We obtained score plots of the metabolites on eighth day of storage by principal component analysis. There was a tendency for groups to be divided on the basis of score plot according to the composition of each gas. PC1 and PC2 seemed to correspond to the influence of O2 and CO2 concentrations, respectively, and the total contribution rate of the two axes was 72%, so that we concluded that the metabolites were affected mainly by O2 and CO2 concentrations. The results indicate that metabolomics may be an effective tool to reveal the relationship between metabolic state of harvested fruits and the atmosphere.

Storage in high-barrier pouches increases the sulforaphane concentration in broccoli florets

Sulforaphane is a phytochemical that is usually found in cruciferous vegetables and is known to have a depressive effect on gastric cancer. Preliminary investigations showed that the sulforaphane concentration in broccoli (Brassica oleracea var. italica) florets increased under anoxia. Therefore, in the present study, we examined the effect of different atmospheric conditions on the sulforaphane concentration in broccoli and also tested whether there are concurrent effects on the concentration of ethanol, which is an unfavorable byproduct of fermentation. The sulforaphane concentration in broccoli florets was significantly elevated by 1.9- to 2.8-fold after 2 d of storage under hypoxia at ca. 0% O₂ and ca. 24% CO₂ at 20°C, whereas no such increase was observed following storage under normoxia at ca. 0% O₂ without CO₂ at 20°C. Furthermore, after 2 d, the sulforaphane concentration under hypoxia was 1.6- to 2.3-fold higher than that under normoxia. These results suggest that storage under hypoxia with high CO₂ levels can elevate the sulforaphane concentration in broccoli florets. However, the elevated sulforaphane concentration could not be maintained beyond 2 d. There was no significant difference in the concentration of ethanol between florets that were stored under hypoxia with/without CO₂ or normoxia at 2 d. However, the ethanol concentrations inside the pouches significantly increased between 2 d and 7 d. These findings indicate that the quality of broccoli florets can be improved through storage under hypoxia with high CO₂ levels at 20°C for 2 d.

Isolation and characterization of rice cesium transporter genes from a rice-transporter-enriched yeast expression library

A considerable portion of agricultural land in central-east Japan has been contaminated by radioactive material, particularly radioactive Cs, due to the industrial accident at the Fukushima Daiichi nuclear power plant. Understanding the mechanism of absorption, translocation and accumulation of Cs⁺ in plants will greatly assist in developing approaches to help reduce the radioactive contamination of agricultural products. At present, however, little is known regarding the Cs⁺ transporters in rice. A transporter-enriched yeast expression library was constructed and the library was screened for Cs⁺ transporter genes. The 1452 full length cDNAs encoding transporter genes were obtained from the Rice Genome Resource Center and 1358 clones of these transporter genes were successively subcloned into yeast expression vectors; which were then transferred into yeast. Using this library, both positive and negative selection screens can be performed, which have not been previously possible. The constructed library is an excellent tool for the isolation of novel transporter genes. This library was screened for clones that were sensitive to Cs⁺ using a SD-Gal medium containing either 30 or 70 mM CsCl; resulting in the isolation of 13 Cs⁺ sensitive clones. ¹³⁷ Cs absorption experiments were conducted and confirmed that all of the identified clones were able to absorb ¹³⁷ Cs. A total of 3 potassium transporters, 2 ABC transporters and 1 NRAMP transporter were among the 13 identified clones.

Identification and quantitative analysis of polyphenolic compounds from the indigo plant (Polygonum tinctorium Lour)

The indigo plant (Polygonum tinctorium Lour) has been used traditionally as a medicinal plant with a variety of biological effects. Of these, polyphenolic ingredients are postulated to contribute to these activities. However, the identification and quantification of polyphenolic compounds in indigo plants have not been conducted comprehensively until now. This study was undertaken to identify the related ingredients by combined instrumental analyses using ultra-performance liquid chromatography electrospray-ionisation mass spectrometry and gas chromatography-mass spectrometry after the extracts of plant tissues were fractionated by absorption column chromatography. These analyses allowed the identification of kaempferol, quercetin-3-O-glucuronide, quercetin, kaempferol-3-O-glucopyranoside, caffeic acid, chlorogenic acid and tentative 3,5,4'-trihydroxy-6,7-methylenedioxyflavone. Furthermore, predominant polyphenolic compounds were quantified by reverse-phase high-performance liquid chromatography and capillary gas chromatography, revealing the higher proportions of kaempferol, quercetin-3-O-glucuronide and quercetin among them. The results indicate that the indigo plant is a promising source for flavonoids and the related compounds with beneficial medicinal effects.

Polypeptone induces dramatic cell lysis in ura4 deletion mutants of fission yeast

Polypeptone is widely excluded from Schizosaccharomyces pombe growth medium. However, the reasons why polypeptone should be avoided have not been documented. Polypeptone dramatically induced cell lysis in the ura4 deletion mutant when cells approached the stationary growth phase, and this phenotype was suppressed by supplementation of uracil. To determine the specificity of this cell lysis phenotype, we created deletion mutants of other genes involved in de novo biosynthesis of uridine monophosphate (ura1, ura2, ura3, and ura5). Cell lysis was not observed in these gene deletion mutants. In addition, concomitant disruption of ura1, ura2, ura3, or ura5 in the ura4 deletion mutant suppressed cell lysis, indicating that cell lysis induced by polypeptone is specific to the ura4 deletion mutant. Furthermore, cell lysis was also suppressed when the gene involved in coenzyme Q biosynthesis was deleted. This is likely because Ura3 requires coenzyme Q for its activity. The ura4 deletion mutant was sensitive to zymolyase, which mainly degrades (1,3)-beta-D glucan, when grown in the presence of polypeptone, and cell lysis was suppressed by the osmotic stabiliser, sorbitol. Finally, the induction of cell lysis in the ura4 deletion mutant was due to the accumulation of orotidine-5-monophosphate. Cell wall integrity was dramatically impaired in the ura4 deletion mutant when grown in the presence of polypeptone. Because ura4 is widely used as a selection marker in S. pombe, caution needs to be taken when evaluating phenotypes of ura4 mutants.

Genetic stability assessment of wWasabi plants regenerated from long-term cryopreserved shoot tips using morphological, biochemical and molecular analysis

This study compared the effect of cryopreserved storage duration of wasabi shoot tips, which derived from the same in vitro mother-plant. We compared the survival of shoot tips and the genetic stability of regenerated plants originating from four experimental groups: shoot tips stored in a -150°C deep-freezer for 10 years; shoot tips stored in liquid nitrogen for 2 h; shoot tips treated with PVS2 vitrification solution; and untreated controls. No significant difference in survival was observed between the four experimental groups. Survival ranged between 93 and 100%. Genetic stability of plants regenerated from cryopreserved shoot tips was assessed over a period of 24 months using morphological, biochemical and molecular markers. While glucose, fructose and glutamic acid concentrations differed slightly between experimental groups after 16 months, these differences disappeared after 24 months. No significant differences were noted for the morphological markers studied (petiole length, shoot number and leaf index). No differences were observed in RAPD profiles obtained with the six primers tested.

Accumulation mechanism of γ-aminobutyric acid in tomatoes (Solanum lycopersicum L.) under low O2 with and without CO2

The storage of ripe tomatoes in low-O(2) conditions with and without CO(2) promotes γ-aminobutyric acid (GABA) accumulation. The activities of glutamate decarboxylase (GAD) and α-ketoglutarate-dependent GABA transaminase (GABA-TK) were higher and lower, respectively, following storage under hypoxic (2.4 or 3.5% O(2)) or adjusted aerobic (11% O(2)) conditions compared to the activities in air for 7 days at 25 °C. GAD activity was consistent with the expression level of mRNA for GAD. The GABA concentration in tomatoes stored under hypoxic conditions and adjusted aerobic conditions was 60-90% higher than that when they are stored in air on the same day. These results demonstrate that upregulation of GAD activity and downregulation of GABA-TK activity cause GABA accumulation in tomatoes stored under low-O(2) conditions. Meanwhile, the effect of CO(2) on GABA accumulation is probably minimal.

Structural analysis of A-type or B-type highly polymeric proanthocyanidins by thiolytic degradation and the implication in their inhibitory effects on pancreatic lipase

Compared with oligomeric proanthocyanidins, highly polymeric proanthocyanidins have more difficulty to analyze the molecular sizes and the mode of interflavan linkages of flavan-3-ol units through doubly linked A-type bonds and single B-type bonds. Recently, we have shown that seed shells of the Japanese horse chestnut contain highly polymeric proanthocyanidins as dominant polyphenolics that can be separated into two fractions according to the difference in the molecular sizes. Here, we tried to perform the structural characterization of them in terms of the molecular sizes and the proportions of A-type linkages relative to B-type linkages. The results were compared with those of the corresponding preparations with variations in the sizes from fruits of blueberry and cranberry. Gel permeation chromatography revealed that the molecular sizes of them were higher in the order of blueberry > cranberry > seed shells of the Japanese horse chestnut when they are compared between the respective fractions. For the analysis of terminal and extension units of those proanthocyanidins, the isolated fractions were subjected to the thiolytic cleavage of the B-type linkages using 1-dodecanethiol, and the resulting degradation products were identified by ultra-performance liquid chromatography electrospray-ionization mass spectrometry (UPLC-ESI/MS). These analyses provided fast and good resolution of the degradation products and revealed higher proportions of A-type linkages compared with B-type linkages in the both isolated fractions in the order of the seed shells > cranberry > blueberry. Moreover, the isolated fractions with higher molecular sizes and those more abundant in the proportions of A-type linkages were found to be more effective in the inhibition of pancreatic lipase activity. The results suggest that higher molecular sizes and more abundance of A-type bonds in polymeric proanthocyanidins are promising key factors for the attenuation of lipid digestion as dietary supplements.

Biochemical mechanism on GABA accumulation during fruit development in tomato

A large amount of gamma-aminobutyric acid (GABA) was found to accumulate in tomato (Solanum lycopersicum) fruits before the breaker stage. Shortly thereafter, GABA was rapidly catabolized after the breaker stage. We screened the GABA-rich tomato cultivar 'DG03-9' which did not show rapid GABA catabolism after the breaker stage. Although GABA hyperaccumulation and rapid catabolism in fruits is well known, the mechanisms are not clearly understood. In order to clarify these mechanisms, we performed comparative studies of 'Micro-Tom' and 'DG03-9' fruits for the analysis of gene expression levels, protein levels and enzymatic activity levels of GABA biosynthesis- and catabolism-related enzymes. During GABA accumulation, we found positive correlations among GABA contents and expression levels of SlGAD2 and SlGAD3. Both of these genes encode glutamate decarboxylase (GAD) which is a key enzyme of GABA biosynthesis. During GABA catabolism, we found a strong correlation between GABA contents and enzyme activity of alpha-ketoglutarate-dependent GABA transaminase (GABA-TK). The contents of glutamate and aspartate, which are synthesized from GABA and glutamate, respectively, increased with elevation of GABA-TK enzymatic activity. GABA-TK is the major GABA transaminase form in animals and appears to be a minor form in plants. In 'DG03-9' fruits, GAD enzymatic activity was prolonged until the ripening stage, and GABA-TK activity was significantly low. Taken together, our results suggest that GAD and GABA-TK play crucial roles in GABA accumulation and catabolism, respectively, in tomato fruits.

Genome wide cDNA-AFLP analysis of genes rapidly induced by combined sucrose and ABA treatment in rice cultured cells

We identified 27 genes induced by combined sucrose and ABA treatment from rice cultured cells with cDNA-AFLP. Thirteen of these up-regulated genes were induced 30 min after the co-treatment. This suite of genes includes starch biosynthesis related genes. Type A genes were expressed only in the presence of both sucrose and ABA. Type B genes were expressed in the presence of sucrose or ABA and the expression was dramatically enhanced by the co-treatment of sucrose and ABA. These results indicate that multiple steps of starch biosynthesis and other processes may be regulated by at least two different pathways.

Gene expression of ADP-glucose pyrophosphorylase and starch contents in rice cultured cells are cooperatively regulated by sucrose and ABA

Six cDNA clones encoding two small subunits and four large subunits of ADP-glucose pyrophosphorylase (AGPase) were mined from the database of rice full-length cDNAs, cloned and subsequently named: OsAPS1, OsAPS2, OsAPL1, OsAPL2, OsAPL3 and OsAPL4. Expression patterns of the six genes were examined by Northern blot analysis with gene-specific probes. OsAPL3 was predominantly expressed in the middle phases of seed development, and OsAPS1, OsAPL1 and OsAPL2 were expressed later in seed development. OsAPS2 and OsAPL4 were constitutively expressed and these isoforms were coordinated with starch accumulation in the developing rice seed. In order to clarify the effect of sugars and plant hormones on AGPase gene expression more precisely, a rice cell culture system was used. OsAPL3 transcript significantly accumulated in response to increased levels of sucrose and abscisic acid (ABA) concentration in the medium; however, the transcripts of other AGPase genes did not show significant accumulation. Under identical conditions, starch contents in the cultured cells also increased. Interestingly, ABA alone did not affect the gene expression of OsAPL3 and starch content. Collectively, these results indicated that the expression level of OsAPL3 and starch content in the cultured cells were cooperatively controlled by alterations in the concentration of both sucrose and ABA.

Rice (Oryza sativa) contains a novel isoform of glutamate decarboxylase that lacks an authentic calmodulin-binding domain at the C-terminus

We have isolated full-length cDNAs for two distinct isoforms of glutamate decarboxylase (GAD), designated OsGAD1 and OsGAD2 from a rice shoot cDNA library. Open reading frames found in OsGAD1 and OsGAD2 cDNAs encode putative proteins of 501 (56.7 kDa) and 500 amino acids (55.6 kDa), respectively. They show 69% identity to each other and 67-78% identity to dicotyledonous counterpart sequences determined so far. Comparative analysis of relevant genomic clones obtained from the rice genomic library with these cDNAs as probes demonstrated that the number and sizes of introns deduced for these two genes differ considerably. Interestingly, in the regions in the putative gene products corresponding to the C-terminal 30-amino-acid peptide known as the calmodulin-binding domain of plant GADs, OsGAD1 possesses a typical motif, while OsGAD2 contains several substitutions of amino acids that contribute strongly to the binding of calmodulin (CaM). An in vitro CaM-binding assay of these proteins over-expressed in Escherichia coli revealed that OsGAD1 can in fact bind specifically to bovine CaM but OsGAD2 cannot. RNA analysis showed that transcripts of OsGAD1 and OsGAD2 were present in all tissues examined, but their expression was differentially regulated, at least in roots and maturing seeds.