Strigolactones (SLs) are a group of terpenoid lactones that are derived from carotenoids. SLs have been found in a number of plant species and appear to serve several diverse physiological functions. SLs were first identified by their ability to stimulate seed germination of root-parasitic plants. Later, SLs were isolated as hyphal-branching inducers of arbuscular mycorrhizal fungi, which facilitate the uptake of soil nutrients by plants. Most recently, SLs (or their derivatives) were found to be a new class of plant hormones that inhibit shoot branching. Considering these three roles of SLs, it was unclear at first why communication signals in the rhizosphere would regulate shoot branching in the host plant. Recent reports, however, suggest that plants produce SLs in response to nitrogen and phosphorus deficiency, stimulating changes in plant shoot and root architecture that enable them to adapt to environmental conditions. Excess SLs produced in roots are released into the soil, where they stimulate the growth of arbuscular mycorrhizal fungi. These symbiotic fungi supply inorganic nutrients that can be used by the plant. This review paper focuses on the physiological roles of SLs as a key regulator of nutrient allocation in plants.
CONSTANS (CO) is a regulator of photoperiodic flowering that activates the transcription of a florigen gene, FLOWERING LOCUS T (FT), in Arabidopsis. CO belongs to the CO/CONSTANS-LIKE (COL) protein family, which consists of 17 proteins and is subclassified into three groups. Here, we characterized the gene for one of the group II members, COL8. The COL8 mRNA accumulated in seeds, leaves, flowers, and siliques. Transgenic Arabidopsis plants with a beta-glucuronidase (GUS) reporter gene driven by a 3-kb COL8 promoter displayed strong GUS activity in leaves. Both transiently and stably produced fluorescence-tagged COL8 proteins were localized in the nucleus. Transgenic Arabidopsis plants possessing COL8 cDNA driven by a cauliflower mosaic virus (CaMV) 35S promoter did not show any altered circadian rhythm under constant light conditions, but showed a late-flowering phenotype under long-day conditions. In these transgenic plants, CO mRNA did not decrease from zeitgeber time (zt) 12 to zt 16, whereas FT mRNA decreased from zt 8 to zt 24. The possible mechanisms for the late-flowering phenotype of the COL8 plants driven by the CaMV 35S promoter are discussed.
We found a novel indolebutyric acid (IBA) derivative, 4-(3-indolyl)butanolide (IBL), produced at an early stage during Bupleurum falcatum L. (known as Saiko in Japan) root culturing. Another IBA derivative, 4-[3-(2-oxo-indolyl)]butyric acid, was also detected, but this compound appeared to have an abiotic origin. Synthetic IBL induced rooting in cultured roots of B. falcatum and induced rooting in cuttings of Vigna radiata. The root-inducing characteristics of IBA and IBL were different. IBA induced considerable thickening of the original roots of B. falcatum, because of marked cell expansion and division in the cortical tissue, before new roots emerged, a typical response to auxin. IBL, on the other hand, did not cause cell expansion, but it induced cell division in the cortical tissue as strongly as IBA did. IBL has the potential to become an excellent, industrially used root inducer, and it serves as valuable tool for research on root induction, because of its unique root-inducing activity.
Tomato fruit yield per area in Japan is 88% lower than that in The Netherlands, because higher-yielding tomato cultivars are bred and cultivated in The Netherlands. In this study, we investigated differences between the Japanese common cultivar ‘Reiyou’ and the Dutch high-yielding cultivar ‘Levanzo’ in fruit yield and components contributing to an increase in fruit yield using the low-node-order pinching and high-density plant training system used in Japan. Fresh and dry fruit yield of ‘Levanzo’ were significantly higher than those of ‘Reiyou’. Estimated leaf blade area of the whole plant and solar radiation on individual leaves were higher in the ‘Levanzo’ canopy than in that of ‘Reiyou’. Although transpiration rate and stomatal conductance were similar in the two cultivars during the latter half of the fruit development period, the photosynthetic rate in ‘Levanzo’ was higher than that in ‘Reiyou’ during the fruit development period. The difference in photosynthetic rate was because chlorophyll a and b content had not decreased in ‘Levanzo’ compared with that in ‘Reiyou’ at 50 days after flowering, corresponding to the latter half of the fruit development period. Transcriptional levels of LeSUT1, which determines sucrose loading activity in source leaves, did not differ between the two cultivars. The higher tomato fruit yield of ‘Levanzo’ compared with that of ‘Reiyou’ was caused by a higher photosynthetic rate, increased solar radiation on individual leaves, and the large sink size due to numerous fruits, but not by sucrose loading activity.
MAP3Kδ4 (At4g23050) is a Raf-like mitogen-activated protein kinase kinase kinase (MAP3K) in Arabidopsis thaliana, classified as subgroup B2. The B2 subgroup MAP3Ks have a kinase domain in the C-terminus and a PAS domain in the N-terminal region. PAS domains are found in a variety of proteins and are reported to mediate protein–protein interactions and to sense environmental stimuli. However, the function of MAP3Kδ4 has not yet been determined. We generated transgenic plants constitutively expressing MAP3Kδ4 or its kinase-negative mutant (MAP3Kδ4KN) and characterized their physiological traits. The transgenic plants overexpressing MAP3Kδ4 showed earlier bolting than wild-type plants. They also showed more vigorous growth by both fresh weight and stem length. In contrast, the transgenic plants overexpressing MAP3Kδ4KN showed a highly branched phenotype; MAP3Kδ4 overexpression had no effect on branch number. These results indicated that MAP3Kδ4 is crucial to regulating both plant growth and shoot branching. In addition, MAP3Kδ4 transcripts were found in all Arabidopsis tissues examined and upregulated by auxin treatment in seedlings, suggesting that MAP3Kδ4 functions in an auxin-dependent manner.
The genetic information in the genome of Eucalyptus camaldulensis was investigated by sequencing the genome and the cDNA using a combination of the conventional Sanger method and next-generation sequencing methods, followed by intensive bioinformatics analyses. The total length of the non-redundant genomic sequences thus obtained was 654,922,307 bp consisting of 81,246 scaffolds and 121,194 singlets. These sequences accounted for approximately 92% of the gene-containing regions with an average G+C content of 33.6%. A total of 77,121 complete and partial structures of protein-encoding genes have been deduced. Comparison of the genes mapped on the KEGG pathways or located in the KOG classification with those in other plant species revealed the characteristics of the E. camaldulensis genome, and it was found that 23 pathways contained enzymes present only in the E. camaldulensis genome. Polymorphism analysis using microsatellite markers developed from the genomic sequence data obtained was performed with six Eucalyptus species collected from various parts of the world to estimate their genetic diversity, and the usefulness of these markers was demonstrated. The genomic sequence and accompanying information presented here are expected to serve as valuable resources for the acceleration of fundamental and applied research with Eucalyptus, especially in the fields of paper production and industrial materials. Further information on the genomic and cDNA sequences and microsatellite markers is available at http://www.kazusa.or.jp/eucaly/.
Previous studies indicated that Housaku Monogatari (HM), a plant activator made from yeast cell wall extract, is effective for control of various plant diseases. To investigate the effect of HM treatment on plant gene expression, we tested the expression of defense related gene induction by exploiting tobacco pathogenesis-related protein 1a (PR-1a) gene promoter- and the Arabidopsis plant defensin 1.2 (PDF1.2) gene promoter-luciferase fusions as reporter genes. Transgenic Arabidopsis plants harboring promoter-luciferase fusion genes were treated with HM and the promoter activity was monitored as changes in luciferase activity in planta. Results of bioluminescence monitoring assay indicated that the promoters were activated at different times after the treatment of test plants with HM. Maximum activation of the PR-1a promoter occurred 4 days, and of the PDF1.2 promoter 4 h, after treatment. These results suggest that HM might contain multiple microbe-associated molecular patterns (MAMPs) that activate systemic acquired resistance and induced systemic resistance signaling pathways at different times. This may explain the mechanisms involved in the induction of defense responses against multiple plant pathogens by HM treatment.
Prolonged exposure of plants to a sufficient level of atmospheric nitrogen dioxide (NO2) activates the uptake and metabolism of nutrients that fuel plant growth and development, a phenomenon termed the plant vitalization effect of NO2. This study examined the effect of NO2 on the fruit yield of tomato (Solanum lycopersicum L. cv. Micro-Tom). Double exposure chambers, designated ±NO2 chambers, were placed in a confined greenhouse. The air entering the −NO2 chamber was scrubbed of nitrogen oxides including NO2, and the air entering the +NO2 chamber was supplemented with NO2 (50 ± 10 ppb). Two-week-old tomato seedlings that had been grown in the −NO2 chamber after sowing were then grown in a +NO2 or −NO2 chamber for the remainder of the growth period until 96 days after sowing. Growth in the +NO2 chamber led to a significant increase in fruit yield of approximately 40% as compared to growth in the −NO2 chamber. This increase in fruit yield was accompanied by acceleration of flowering time by 3.2 days and an increase in flower number per plant of up to 60%. These results show that exposure to NO2 increases fruit yield via stimulation of flowering in tomato.
Liverwort, Marchantia polymorpha L. synthesizes various polyunsaturated fatty acids such as arachidonic acid (AA) and eicosapentaenoic acid (EPA), neither of which is produced by higher plants. Here, we report the effects of light quality and intensity on the accumulation of AA and EPA in liverwort. In the range of the light examined, the relative content of EPA to total fatty acid was highest under blue light although that of AA did not vary. Illumination with blue light for a short period efficiently improved the accumulation of EPA without great deficit of growth. At a higher intensity of white light, the relative content of EPA increased. The optimum light intensity for AA and EPA accumulation was found to be 80 photon flux density μmol m−2 s−1.
High expression of transgene is one of the key requirements for the successful establishment of transgenic plants to produce a lot of proteins or metabolites. Although the cauliflower mosaic virus 35S (CaMV35S) promoter and the nopaline synthase (NOS) terminator are often used for this purpose, their efficiencies vary to plant species used. In a liverwort, Marchantia polymorpha L., the CaMV35S promoter and the NOS terminator do not show significant enhancing effect of transgene expression. To construct more efficient gene expression system of the liverwort, we employed the transient gene expression assay system. As a result, the endogenous elongation factor 1α promoter and Flowering locus T1 terminator from the liverwort led to enhance transient gene expression, approximately 75 and 3 times, respectively, compared to the CaMV35S promoter and the NOS terminator. Furthermore, we found that the endogenous 5′-UTR of the liverwort ADH-like UDP glucose dehydrogenase (MpUDP) yielded an enhancement of 15 times greater than in cases without the MpUDP 5′-UTR. These results indicate that DNA elements enhancing gene expression can be obtained efficiently by the transient gene expression assay in a short period of time, promising the application to the transgene expression system for production of proteins and metabolites in the liverwort.
Anther-specific promoters have been extensively studied in terms of the genetic engineering of male-sterile plants. Here, we fused the 5′ upstream promoter regions of a sucrose synthase gene from tomato (TOMSSF) to the β-glucuronidase (GUS) gene and used the construct to transform Chrysanthemum plants. Histochemical analysis of two transformants showed high GUS activity in ray florets and tubular florets. Analysis of the staining pattern in these florets reveled that staining was stamen-specific. GUS gene expression was highest in the stamen and remained at a steady-state level throughout the experiment. These results suggest that the TOMSSF promoter has high activity in the stamen of tubular florets and would be useful as a high stamen-specific promoter in Chrysanthemum.
Apple has a relatively long juvenile growth period, taking approximately 8 years to reach the flowering stage. This period has impeded breeding programs. Since MdTFL1 (an ortholog of TERMINAL FLOWER1) is strongly related to juvenility/vegetative and flower initiation in apple, its studies will provide insight into relationship between phytohormones and juvenile/vegetative growth and flower bud formation. In this study, we monitored expression of the MdTFL1 promoter-β-glucuronidase (GUS) fusion construct in apple tissues in vitro, to determine which plant growth regulators affect its expression. Expression of MdTFL1 was induced strongly throughout newly generated young shoots of cytokinin-treated plants and in apices of shoots on medium containing cytokinin+auxin. These results suggest that cytokinin may induce MdTFL1 expression to maintain the juvenile form at the base of plant, and that cytokinin and auxin determine whether the shoot apical meristem will transit from the vegetative to the reproductive state.
Aquaporins facilitate water flux across biomembranes in cells and are involved in various physiological phenomena in several plant tissues. Generally, the water-flux activity of exogenously expressed aquaporins is measured in Xenopus laevis oocytes or yeast. However, heterogeneous systems are not likely to be optimal for plant aquaporin analysis. Thus, we created a new experimental system for functional analysis of plant aquaporins using lily (Lilium longiflorum) pollen protoplasts. Large protoplasts with uniform diameters of approximately 95 μm were isolated from lily pollen grains. No plasma membrane intrinsic protein (PIP) aquaporin was detected in lily pollen. For ectopic expression of PIPs in the lily pollen protoplasts, we constructed plasmids in which Arabidopsis AtPIP1;1 or AtPIP2;1 was under the control of a strong pollen-specific promoter (maize Zm13). The PCR-amplified DNA fragments were transformed into the pollen protoplasts by electroporation. Between 45 and 60% of protoplasts were successfully transformed. The protoplasts expressing AtPIP2;1 significantly increased in volume in a hypotonic solution (350 mM mannitol), compared with the vector control. In contrast, the changes in volume of the protoplasts expressing AtPIP1;1 were similar to that of the vector control. This result suggests that PIP2 induces higher water-flux activity in plant cells, whereas PIP1 does not. Thus, we propose the lily pollen protoplast as a simple and useful experimental system to analyze the function of plant aquaporins.
Transcriptional gene silencing (TGS) is a phenomenon by which transgenes that share homology in their promoter regions are inactivated. TGS is known to be reduced by using different promoters to drive the expression of each transgene. However, in order to perform a large-scale genetic screen in which overexpression lines are mutagenized by T-DNA tagging and therefore harbor two types of transgene, it is critical to develop a technique that consistently blocks TGS. Here, I report a versatile method that completely prevents TGS in transgenic Arabidopsis. A seedling morphology-based assay demonstrated that TGS could be significantly diminished by using different terminator sequences for each transgene. Furthermore, it was suggested that TGS might be reduced if the orientations of the two T-DNA sequences were reversed relative to each other. By combining these strategies, I showed that TGS was completely blocked in over 50,000 T1 plants. These findings present a thorough and versatile method to prevent TGS that is potentially applicable to various plant species and is expected to be used in diverse situations, from basic to applied research fields.