Although we enjoy convenient and happy lives as a result of using large amount of fossil fuels, this convenience comes at a steep price: global warming, pollution, and destruction of the environment. It took more than a hundred million years for the Earth to accumulate its current reserves of fossil fuels. It is sure that the earth will confuse, if we exhaust it within 1-2 centuries. Solar energy supports all life on the earth, and plants are able to use this energy. Annually, plant biomass produces 8 times as much energy as we consume globally. Therefore, if we could harness 12% of plant biomass for the production of energy and industrial materials, in place of fossil fuels, we could establish a sustainable world. Plant biotechnology is progressing rapidly, and research aimed at producing both fuels and plastics from plant biomass is already underway. Because carbon dioxide generated from plant products will ultimately be consumed by other plants, the recycling system is built in. Our future therefore may not so dark after all.
Cyanobacteria are highly versatile organisms in spite of their small size; they represent the smallest photosynthetic units on Earth, and gave rise to algae and plants. Cyanobacteria are globally widespread in terrestrial and aquatic environments, including the large oceans. In recent years they have attracted attention because of their high evolutionary importance, their developmental complexity, their unexpected pivotal ecological significance in global biogeochemical cycles and their production of a large number of secondary metabolites, many with great biotechnological potential. In this overview, focus is on the role of cyanobacteria in the origin and evolution of algae and plants, and on mechanisms in contemporary cyanobacterial-plant symbioses (Gunnera and Azolla) that may represent ‘blue-prints’ of those that some 2.1 billion years ago became the first chloroplasts.
Cyanobacteria are now recognized as the primary nitrogen-fixing (diazotrophic) microorganisms in the oceans as contributing significantly to the biogeochemistry of the global nitrogen cycle. The evolution of a remarkable range of morphologies and metabolic capacities has led to a behavioural versatility that helps them to proliferate and combat nutrient limitations in oceanic ecosystems. Advancement in community gene, genome and metagenome analyses of marine microbial communities will further advance functional interpretations and biotechnological uses. In this review we highlight the diversity, adaptation and function of cyanobacteria in the ocean.
The non-protein amino acid β-N-methyl-amino-L-alanine (BMAA) is a neurotoxin that was recently found to be produced by most cyanobacteria. The neurotoxin was discovered in 1967 in the seeds of the cycad Cycas micronesica, but this BMAA may originate from the symbiotic cyanobacterium Nostoc, which inhabits the roots of cycads. BMAA is thought to be the cause of the deadly neurodegenerative disease amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC), common among the Chamorro people of Guam. It was demonstrated that the Chamorros, in all probability, have been exposed to high levels of BMAA through dietary consumption of flying foxes which fed mainly on cycads seeds. BMAA production may be a common conserved evolutionary feature among cyanobacteria and due to their wide global distribution, the toxin may be a common concern and potentially involved in provoking degenerative diseases worldwide. BMAA may likewise be bioaccumulated in other cyanobacterial based food webs within ecosystems outside Guam, and it is proposed that such webs may exist in the Baltic Sea, with its massive occurrence of cyanobacteria (blooms).
Excessive sodium (Na+) accumulation in plants due to soil salinity is toxic to most higher plants including crop plants. Many genes encoding Na+ permeable transporters/channels have been identified for the last 15 years, based on genetic approaches, genome-sequencing projects and functional complementation screening using yeast mutants. The HKT-type transporter/channel class is one of the best characterized Na+ permeable membrane proteins in plants. Interestingly, most Na+ permeable proteins including HKT-type transporters/channels in plants were shown or deduced to play a protective role against salinity stress. A Na+ selective transporter/channel in rice (Oryza sativa), OsHKT2;1, however, has recently been proven to function in “nutritional Na+ absorption” in K+-starved roots rather than functioning in a protective role under salinity stress. Here we review findings on the HKT-type transporters/channels, mainly focusing on the function of OsHKT2;1 that is tightly regulated by K+/Na+ homeostatic mechanisms of rice plants. We also discuss functions of Arabidopsis thaliana AtHKT1;1 and rice OsHKT1;5 in protecting plant leaves from over-accumulating toxic Na+ concentrations during salinity stress by removing Na+ from the xylem sap.
Regulation of K+/Na+ homeostasis is an important mechanism in plant growth. The high-affinity K+ uptake system plays a central role in this mechanism especially when plants experience environmental stresses of K+ starvation and high salinity. K+ channels and the K+/Na+ co-transporter like HKT have been closely studied as principal members of the K+ transport system in plants. The KT/HAK/KUP family is a major K+ transporter family present in bacteria, fungi and plants. In plants, the KT/HAK/KUP transporters form a large family. Arabidopsis thaliana has 13 genes and rice has at least 25. KT/HAK/KUP transporters serve various functions in various K+ traffic, but their physiological roles are still unclear. Plant KT/HAK/KUP transporters could be divided into 4 related clusters according to their amino acid sequences, the character of transporters belongs to each cluster was summarized. We analyzed the expression of OsHAK genes in rice roots under both K+ starvation and salt stress conditions.
The present review focuses on two important aspects of Na+ toxicity in rice (Oryza sativa L.), (i) that Na+ stress induces different changes in cytosolic Ca2+, [Ca2+]cyt, and pH, [pH]cyt, in tolerant and sensitive cultivars, and (ii) that cells from a tolerant cultivar can better maintain a low cytosolic Na+ and/or Na+/K+ ratio. Experiments with single rice protoplasts, fluorescence microscopy and specific ion-selective dyes suggest that Na+ must be sensed inside the cytosol, before any prolonged changes in [Ca2+]cyt and [pH]cyt occur. Inhibitor analyses show that Na+-induced increase in [pH]cyt in the tolerant cv. Pokkali, and a decrease in [pH]cyt in the sensitive cv. BRRI DHan29, likely are coupled to different H+-ATPases. Expression analysis of OsHKT2;1 (previous name OsHKT1), OsHKT2;2 (previous name OsHKT2) and OsVHA transcripts in rice using RT-PCR and fluorescence in situ-PCR, shows a variable and cell- specific induction in the two rice cultivars under salt stress condition. We conclude that the transient uptake of Na+, which occurs only in the tolerant cultivar, and the fast compartmentalization of Na+ into the vacuole, probably are the most important cellular traits for Na+-tolerance in rice. The low [Na+]cyt in cv. Pokkali might depend on the fast down-regulation of OsHKT2;1, causing less uptake of Na+, and fast up-regulation of the OsVHA transcript, and subsequent activation of the Na+/H+-anti-porter in the tonoplast. To decrease the cytosolic Na+/K+ ratio under Na+ toxicity, cv. Pokkali may also induce increased uptake of K+ through induction of OsHKT2;2, and other specific K+-transporter genes.
Drought is one of the major environmental factors restricting plant productivity worldwide. Under drought in the presence of strong light, plants are liable to be damaged by excessively-absorbed solar energy as well as dehydration of their tissues. Wild plants found in the arid zones are equipped with specialized mechanisms for either avoiding or tolerating drought, and successfully adapt to the harsh environments. Recent molecular studies on the wild plants have shed new lights on the unique features of their resistance mechanisms, which are markedly different from those found in the model and/or domesticated crop plants.
Corky root rot (CRR) is an escalating plant disease of tomato (Solanum esculentum), caused by a soil-borne fungus, Pyrenochaeta lycopersici. During the last two decades there have almost been no progress in the understanding of the molecular mechanisms promoting infection and plant susceptibility. As there are no CRR-resistant lines of cultivated tomato on the market and no other known means for plant protection, a deeper molecular knowledge about the infection process is urgently needed. We have therefore outlined an efficient strategy to search for corky root rot-resistance genes in wild tomato. In addition, we are investigating the genetic determinants for infection and virulence of the fungal pathogen, P. lycopersici. In this review we summarize the quite limited molecular knowledge about the pathogen and the disease, and discuss the possibilities to overcome previous technical obstacles in this new era of molecular biology.
In the endoplasmic reticulum (ER) stress response, protein folding in the ER is disturbed, resulting in the induction of genes encoding proteins that facilitate correct folding of proteins. Unique mechanism of signaling pathway in the ER stress response has been studied in yeast and animals. In animals, several bZIP type transcription factors with a transmembrane domain controlled by regulated intramembrane proteolysis (RIP) have been reported to be involved in the signaling pathway. Very recently, AtbZIP60, which is a bZIP type transctiption factor with a transmembrane domain, was identified to be involved in the ER stress response in Arabidopsis. Several other transctiption factors that seem to be regulated by RIP have been also reported in Arabidopsis. Analysis of the regulation mechanism of AtbZIP60 will contribute to understanding of the ER stress response and RIP in plants.
The timing of floral transition, which is directly related to reproductive fitness, is regulated by many environmental factors. Transduction of these environmental signals is sensed in several tissues as the primary adaptive signal for flowering, integrated into the plant's florigenic signaling pathway, and transmitted to the shoot apex, where the transition to reproductive organ development is initiated. Recent studies have identified the mobile signal, florigen, for photoperiod-dependent flowering, which is conserved between long-day plants (Arabidopsis) and short-day plants (rice). Vernalization also controls the flowering time of Arabidopsis by modifying the chromatin of the flowering repressor gene. Here, we review the molecular mechanisms that control photoperiodic flowering associated with the FT-like gene family, including epigenetic regulation in rice.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) catalyses the initial step of photosynthetic CO2 assimilation, although its catalytic efficiency is very low. Therefore, higher plants must synthesize large amounts of RuBisCO to compensate for its inefficient enzymatic properties. The holoenzyme of RuBisCO consists of 8 large and 8 small subunits, whose genes are individually encoded on two distinct genomes located in the chloroplast and the nucleus, respectively. RuBisCO biosynthesis requires many factors involved in transcription, translation, folding and assembly processes. However, the mechanisms underlying these processes are complex, and therefore the molecular mechanisms and regulation systems of RuBisCO biosynthesis are not yet fully understood. In this review, we introduce recent research on the molecular mechanisms of RuBisCO biosynthesis in higher plants, and discuss future perspectives in this field of research.
In root nodule symbioses, bacterial microsymbionts are hosted inside plant cells and supply the host plant with the products of biological nitrogen fixation, rendering it independent of soil nitrogen sources. Two types of such interactions are known, legume/rhizobia symbioses involving several alpha- and beta-proteobacterial genera, collectively called rhizobia, and members of the Leguminosae (Fabaceae) family, and actinorhizal symbioses involving members of the Gram-positive actinomycetous genus Frankia and a diverse group of plants from 25 genera from eight different families, collectively called actinorhizal plants, with one exception trees or woody shrubs.
The abundance of chitinases in plants is surprising in view of the fact that plants do not contain chitin. However, plant chitinases have been shown to play a role in defense, growth and developmental processes. They are also involved in plant-bacterial symbioses. Two groups of plants, legumes and actinorhizal plants, are able to enter root-nodule symbioses with nitrogen fixing bacteria, rhizobia and Frankia strains, respectively, and plant chitinases are involved in these interactions. None of these bacteria contain chitin in their cell walls but rhizobia produce chitinaceous signal factors. To find out whether symbiosis-related chitinases belonged to phylogenetically distinct subgroups, a phylogenetic analysis was performed including all chitinases of one dicot, Arabidopsis, and one monocot, rice. The results show that conserved class I- and class III-chitinases were recruited in both types of root nodule symbioses. Since no chitinaceous signal molecules are formed by Frankia, a role of chitinases in the control of microbial signaling is unlikely. Alternative roles of chitinases in root nodules are discussed.
To establish a sustainable society, forest biomass or lignocellulosic biomass, which is the most abundantly accumulated biomass resource, plays an important role. Therefore it is critically important to establish systems for sustainable production of forest biomass, especially tropical forest resources. Forest tree biotechnology will play a very important role in such systems. Following the completion of whole genome sequence of Populus, tree bioscience and biotechnology have entered into “post-genomic era”. However, although tropical Acacia is one of the most important tropical plantation tree in Indonesia and Malaysia, its biotechnology is still at a primitive stage. Because the Acacia mangium genome sequence data base is far beyond the ability of university laboratories, it is important to construct expressed-sequence tag (EST) data bases for Acacia. A. mangium EST data bases are quite useful for identifying genes that are possibly involved in the expression of a given trait, and can be exploited to detect Acacia genes which are orthologous to those of other model plants that are involved in secondary xylem formation. In addition, establishing efficient systems for in vitro regeneration of transformed Acacia and identification of genes and metabolites responsible for expression of commercially important traits are indispensable for genetic modification of the species. Importantly, these activities must be done to benefit global environment conservation and social welfare of local communities. In this review, the current status of Acacia biotechnology is outlined.
Cellulose plays a central role in plant development and its biosynthesis represents one of the most important biochemical processes in plant biology. However, the corresponding molecular mechanisms are not well understood, despite the progress made in the past years in the identification of genes that code for the catalytic subunits of the cellulose synthases and other proteins potentially involved in cellulose formation. A major bottleneck is the high instability of the cellulose synthase complexes and their location in the plasma membrane. Additional efforts are currently being made to unravel the mechanisms of cellulose biosynthesis. Indeed, understanding how cellulose is formed and how its crystallinity is achieved is relevant not only for studying plant development, but also for improving the digestibility of the plant biomass, which is foreseen as an alternative to fossil fuels for the production of energy. This review summarizes the major unanswered questions related to the process of cellulose biosynthesis, and describes the recent progress that has been made in the area through the combination of biochemical approaches and molecular genetics.