Yuko Ohashi

Bio: Yuko Ohashi is an academic researcher from Hokkaido University. The author has contributed to research in topics: Gene & Tobacco mosaic virus. The author has an hindex of 50, co-authored 112 publications receiving 8206 citations.

A large family of class III plant peroxidases.

Abstract: 3Core Research for Evolutional Science and Technology (CREST), Chiyoda-ku, Tokyo, 101-0062 Japan ; Class III plant peroxidase (POX), a plant-specific oxidoreductase, is one of the many types of peroxidases that are widely distributed in animals, plants and microorganisms. POXs exist as isoenzymes in individual plant species, and each isoenzyme has variable amino acid sequences and shows diverse expression profiles, suggesting their involvement in various physiological processes. Indeed, studies have provided evidence that POXs participate in lignification, suberization, auxin catabolism, wound healing and defense against pathogen infection. Little, however, is known about the signal transduction for inducing expression of the pox genes. Recent studies have provided information on the regulatory mechanisms of wound- and pathogen-induced expression of some pox genes. These studies suggest that pox genes are induced via different signal transduction pathways from those of other known defense-related genes.

Efficient promoter cassettes for enhanced expression of foreign genes in dicotyledonous and monocotyledonous plants.

Abstract: A series of chimeric promoters for higher-level expression of foreign genes in plants was constructed as fusions of a gene for beta-glucuronidase (GUS) with the terminator of a gene for nopaline synthase (nos) or of the cauliflower mosaic virus (CaMV) 35S transcript, and the strength of these promoters was assayed in transient and stable expression systems in tobacco and rice. As parts of these promoters, the CaMV 35S core promoter, three different 5'-upstream sequences of the 35S promoter, the first intron of a gene for phaseolin, and a 5'-untranslated sequence (omega sequence) of tobacco mosaic virus were used in various combinations. In tobacco and rice protoplasts, all three fragments of the 35S promoter (-419 to -90, -390 to -90 and -290 to -90, relative to the site of initiation of transcription), the intron, and the omega sequence effectively enhanced GUS activity. Some chimeric promoters allowed levels of GUS activity that were 20- to 70-fold higher than those obtained with the 35S promoter in pBI221. In tobacco protoplasts, the two longer fragments of the 35S promoter were more effective than the shortest fragment. In rice cells, by contrast, the shortest fragment was as effective as the two longer ones. The terminator of the 35S transcript was more effective than that of the nos gene for gene expression. In transgenic tobacco plants, a representative powerful promoter, as compared to the 35S promoter, allowed 10- and 50-fold higher levels of expression on average and at most, respectively, with no clear qualitative differences in tissue- and organ-specific patterns of expression. When the representative promoter was introduced into tobacco with a gene for luciferase, the autofluorescence of detached leaves after a supply of luciferin to petioles was great and was easily detectable by the naked eye in a dark room.

Antagonistic Effect of Salicylic Acid and Jasmonic Acid on the Expression of Pathogenesis-Related (PR) Protein Genes in Wounded Mature Tobacco Leaves

Abstract: Salicylic acid (SA) and jasmonic acid (JA) are essential compounds in the pathogen- and wound-signaling path­ ways accompanying induced expression of acidic and basic pathogenesis-related (PR) protein genes, respectively. How­ ever, on the effect of exogenously supplied SA and JA in in­ duction of PR gene expression, conflicting results have been obtained using various plant materials at different de­ velopmental stages. There is no clear evidence on these effects in the presence of both signals at the same time. We analyzed the effect of SA on wound- and JA-induced basic PR gene expression and that of JA on SA-induced acidic PR gene expression in mature tobacco leaves. Wound-in­ duced accumulation of transcripts for all 4 basic PR genes tested was enhanced in the presence of MeJA, and in­ hibited in the presence of SA. On the other hand, expres­ sion of all 3 acidic PR genes tested was induced by SA and was inhibited by MeJA. Using antibodies raised against acidic PR-l and PR-2 proteins, these effects were confirm­ ed at the protein level. These results indicated that JA works as an inducer of basic PR genes, and also as an inhib­ itor for acidic PR genes, while SA does the opposite.

DNA binding and dimerization specificity and potential targets for the TCP protein family

Abstract: Summary The TCP domain is a plant-specific DNA binding domain found in proteins from a diverse array of species, including the cycloidea (cyc) and teosinte branched1 (tb1) gene products and the PCF1 and PCF2 proteins. To understand the role in transcriptional regulation of proteins with this domain, we have analysed the DNA binding and dimerization specificity of the TCP protein family using rice PCF proteins, and further evaluated potential targets for the TCP protein. The seven PCF members including five newly isolated proteins, were able to be grouped into two classes, I and II, based on sequence similarity in the TCP domain. Random binding site selection experiments and electrophoretic mobility shift assays (EMSAs) revealed the consensus DNA binding sequences of these two classes to be distinct but overlapping; GGNCCCAC for class I and GTGGNCCC for class II. The TB1 protein from maize, which belongs to class II, had the same specificity as the rice class II proteins, suggesting the conservation of binding specificity between TCP domains from different species. The yeast 2-hybrid assay and EMSA revealed that these proteins tend to form a homodimer or a heterodimer between members of the same class. We searched predicted 5¢ flanking sequences of Arabidopsis genes for the consensus binding sequences and found that the consensus sites are distributed in the genome at a considerably lower frequency. We further analysed eight promoters containing the class I consensus TCP sites. The transcriptional activities of six promoters were decreased by a mutation of the TCP binding site, which is consistent with the observation that the class I TCP site can confer transactivation function on a heterologous promoter. These results suggest that the two classes of TCP protein are distinct in DNA binding specificity and transcriptional regulation.

REACTIVE OXYGEN SPECIES: Metabolism, Oxidative Stress, and Signal Transduction

Abstract: Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of aerobic metabolism. Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Whereas plants are surfeited with mechanisms to combat increased ROS levels during abiotic stress conditions, in other circumstances plants appear to purposefully generate ROS as signaling molecules to control various processes including pathogen defense, programmed cell death, and stomatal behavior. This review describes the mechanisms of ROS generation and removal in plants during development and under biotic and abiotic stress conditions. New insights into the complexity and roles that ROS play in plants have come from genetic analyses of ROS detoxifying and signaling mutants. Considering recent ROS-induced genome-wide expression analyses, the possible functions and mechanisms for ROS sensing and signaling in plants are compared with those in animals and yeast.

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Abstract: Reactive oxygen species (ROS) are produced as a normal product of plant cellular metabolism. Various environmental stresses lead to excessive production of ROS causing progressive oxidative damage and ultimately cell death. Despite their destructive activity, they are well-described second messengers in a variety of cellular processes, including conferment of tolerance to various environmental stresses. Whether ROS would serve as signaling molecules or could cause oxidative damage to the tissues depends on the delicate equilibrium between ROS production, and their scavenging. Efficient scavenging of ROS produced during various environmental stresses requires the action of several nonenzymatic as well as enzymatic antioxidants present in the tissues. In this paper, we describe the generation, sites of production and role of ROS as messenger molecules as well as inducers of oxidative damage. Further, the antioxidative defense mechanisms operating in the cells for scavenging of ROS overproduced under various stressful conditions of the environment have been discussed in detail.

Plant responses to drought, salinity and extreme temperatures: towards genetic engineering for stress tolerance

Abstract: Abiotic stresses, such as drought, salinity, extreme temperatures, chemical toxicity and oxidative stress are serious threats to agriculture and the natural status of the environment. Increased salinization of arable land is expected to have devastating global effects, resulting in 30% land loss within the next 25 years, and up to 50% by the year 2050. Therefore, breeding for drought and salinity stress tolerance in crop plants (for food supply) and in forest trees (a central component of the global ecosystem) should be given high research priority in plant biotechnology programs. Molecular control mechanisms for abiotic stress tolerance are based on the activation and regulation of specific stress-related genes. These genes are involved in the whole sequence of stress responses, such as signaling, transcriptional control, protection of membranes and proteins, and free-radical and toxic-compound scavenging. Recently, research into the molecular mechanisms of stress responses has started to bear fruit and, in parallel, genetic modification of stress tolerance has also shown promising results that may ultimately apply to agriculturally and ecologically important plants. The present review summarizes the recent advances in elucidating stress-response mechanisms and their biotechnological applications. Emphasis is placed on transgenic plants that have been engineered based on different stress-response mechanisms. The review examines the following aspects: regulatory controls, metabolite engineering, ion transport, antioxidants and detoxification, late embryogenesis abundant (LEA) and heat-shock proteins.