An ATP Binding Cassette Transporter Is Required for Cuticular Wax Deposition and Desiccation Tolerance in the Moss Physcomitrella patens

The plant cuticle is thought to be a critical evolutionary adaptation that allowed the first plants to colonize land, because of its key roles in regulating plant water status and providing protection from biotic and abiotic stresses. Much has been learned about cuticle composition and structure through genetic and biochemical studies of angiosperms, as well as underlying genetic pathways, but little is known about the cuticles of early diverging plant lineages. Here, we demonstrate that the moss Physcomitrella patens, an extant relative of the earliest terrestrial plants, has a cuticle that is analogous in both structure and chemical composition to those of angiosperms. To test whether the underlying cuticle biosynthetic pathways were also shared among distant plant lineages, we generated a genetic knockout of the moss ATP binding cassette subfamily G (ABCG) transporter Pp-ABCG7, a putative ortholog of Arabidopsis thaliana ABCG transporters involved in cuticle precursor trafficking. We show that this mutant is severely deficient in cuticular wax accumulation and has a reduced tolerance of desiccation stress compared with the wild type. This work provides evidence that the cuticle was an adaptive feature present in the first terrestrial plants and that the genes involved in their formation have been functionally conserved for over 450 million years.     

A chalcone isomerase‐like protein enhances flavonoid production and flower pigmentation

Flavonoids are major pigments in plants, and their biosynthetic pathway is one of the best‐studied metabolic pathways. Here we have identified three mutations within a gene that result in pale‐colored flowers in the Japanese morning glory (Ipomoea nil). As the mutations lead to a reduction of the colorless flavonoid compound flavonol as well as of anthocyanins in the flower petal, the identified gene was designated enhancer of flavonoid production (EFP). EFP encodes a chalcone isomerase (CHI)‐related protein classified as a type IV CHI protein. CHI is the second committed enzyme of the flavonoid biosynthetic pathway, but type IV CHI proteins are thought to lack CHI enzymatic activity, and their functions remain unknown. The spatio‐temporal expression of EFP and structural genes encoding enzymes that produce flavonoids is very similar. Expression of both EFP and the structural genes is coordinately promoted by genes encoding R2R3‐MYB and WD40 family proteins. The EFP gene is widely distributed in land plants, and RNAi knockdown mutants of the EFP homologs in petunia (Petunia hybrida) and torenia (Torenia hybrida) had pale‐colored flowers and low amounts of anthocyanins. The flavonol and flavone contents in the knockdown petunia and torenia flowers, respectively, were also significantly decreased, suggesting that the EFP protein contributes in early step(s) of the flavonoid biosynthetic pathway to ensure production of flavonoid compounds. From these results, we conclude that EFP is an enhancer of flavonoid production and flower pigmentation, and its function is conserved among diverse land plant species.     

The cell biology of charophytes: Exploring the past and models for the future

Charophytes (Streptophyta) represent a diverse assemblage of extant green algae that are the sister lineage to land plants. About 500–600+ million years ago, a charophyte progenitor successfully colonized land and subsequently gave rise to land plants. Charophytes have diverse but relatively simple body plans that make them highly attractive organisms for many areas of biological research. At the cellular level, many charophytes have been used for deciphering cytoskeletal networks and their dynamics, membrane trafficking, extracellular matrix secretion, and cell division mechanisms. Some charophytes live in challenging habitats and have become excellent models for elucidating the cellular and molecular effects of various abiotic stressors on plant cells. Recent sequencing of several charophyte genomes has also opened doors for the dissection of biosynthetic and signaling pathways. While we are only in an infancy stage of elucidating the cell biology of charophytes, the future application of novel analytical methodologies in charophyte studies that include a broader survey of inclusive taxa will enhance our understanding of plant evolution and cell dynamics.

Charophytes constitute a diverse array of green algal taxa that provide critical insight into plant evolution and offer exciting opportunities for multiple levels of study in plant cell biology.     

Metabolic engineering of astaxanthin production in tobacco flowers

Using metabolic engineering, we have modified the carotenoid biosynthesis pathway in tobacco (Nicotiana tabacum) to produce astaxanthin, a red pigment of considerable economic value. To alter the carotenoid pathway in chromoplasts of higher plants, the cDNA of the gene CrtO from the alga Haematococcus pluvialis, encoding beta-carotene ketolase, was transferred to tobacco under the regulation of the tomato Pds (phytoene desaturase) promoter. The transit peptide of PDS from tomato was used to target the CRTO polypeptide to the plastids. Chromoplasts in the nectary tissue of transgenic plants accumulated (3S,3'S) astaxanthin and other ketocarotenoids, changing the color of the nectary from yellow to red. This accomplishment demonstrates that plants can be used as a source of novel carotenoid pigments such as astaxanthin. The procedures described in this work can serve as a platform technology for future genetic manipulations of pigmentation of fruits and flowers of horticultural and floricultural importance.     

Function and evolution of 'green' GSK3/Shaggy-like kinases

Glycogen synthase kinase 3 (GSK3) proteins, also known as SHAGGY-like kinases, have many important cell signalling roles in animals, fungi and amoebae. In particular, GSK3s participate in key developmental signalling pathways and also regulate the cytoskeleton. GSK3-encoding genes are also present in all land plants and in algae and protists, raising questions about possible ancestral functions in eukaryotes. Recent studies have revealed that plant GSK3 proteins are actively implicated in hormonal signalling networks during development as well as in biotic and abiotic stress responses. In this review, we outline the mechanisms of Arabidopsis GSK3 action, summarize GSK3 functions in dicot and monocot flowering plants, and speculate on the possible functions of GSK3s in the earliest-evolving land plants.     

Mechanisms underlying flower color variation in Asian species of Meconopsis: A preliminary phylogenetic analysis based on chloroplast DNA and anthocyanin biosynthesis genes

The Qinghai–Tibet Plateau (QTP) harbors the highest species diversity of alpine plants in the world, with a spectacular diversity of flower colors. Among these QTP plants, the genus Meconopsis comprises more than 50 species, for which flower color is a key diagnostic character. However, the mechanisms underlying flower color variation have rarely been investigated. In the present study, we used three chloroplast (cp) DNA fragments and two anthocyanin biosynthesis genes (F3H andF3′H) for phylogenetic reconstruction of Meconopsis. We revealed the presence of three well-supported clades and/or subclades in the cpDNA and nuclear gene trees; further, flower color transition occurred in each lineage. The results of selection tests and preliminary expression analyses of the anthocyanin biosynthesis genes indicate that the pigment pathway leading to cyanidin is active in blue and red flowers of Meconopsis; further, a blue–red color shift is not attributable to an on/off switching of the anthocyanin biosynthetic pathway (ABP) branches. Together with the results of previous flower pigment analyses, our findings suggest that blue–red flower color transitions in Meconopsis are attributable to modification of cyanidin. Our molecular dating results indicate that the lineage diversification inMeconopsis is closely related to the QTP uplift; thus, it is likely that environmental changes arising from the QTP uplift have played important roles in driving the diversification of flavonoids, through which species of Meconopsis have adapted physiologically to diverse habitats.     

Increased accumulation and decreased catabolism of anthocyanins in red grape cell suspension culture following magnesium treatment

Anthocyanins are the largest and best studied group of plant pigments. However, not very much is known about the fate of these phenolic pigments after they have accumulated in the cell vacuoles of plant tissues. We have previously shown that magnesium treatment of ornamentals during the synthesis of anthocyanins in the flowers or foliage caused an increase in the pigment concentration. In this study, we characterized the effect of magnesium on the accumulation of anthocyanin in red cell suspension originating from Vitis vinifera cv. Gamay Red grapes. Magnesium treatment of the cells caused a 2.5- to 4.5-fold increase in anthocyanin concentration, with no substantial induction of the biosynthetic genes. This treatment inhibited the degradation of anthocyanins occurring in the cells, and changed the ratio between different anthocyanins determining cell color, with an increase in the relative concentration of the less stable pigment molecules. The process by which magnesium treatment affects anthocyanin accumulation is still not clear. However, the results presented suggest at least part of its effect on anthocyanin accumulation stems from inhibition of the pigments’ catabolism. When anthocyanin biosynthesis was inhibited, magnesium treatments prevented the constant degradation of anthocyanins in the cell suspension. Future understanding of the catabolic processes undergone by anthocyanins in plants may enable more efficient inhibition of this process and increased accumulation of these pigments, and possibly of additional phenolic compounds.     

Flavonoids and Melanins: A Common Strategy across Two Kingdoms

Ultraviolet (UV) radiations alter a number of metabolic functions in vivant. They produce damages to lipids, nucleic acids and proteins, generating reactive oxygen species such as singlet oxygen (O₂), hydroxyl radical (HO) and superoxide anion (O₂^-). Plants and animals, after their water emersion, have developed biochemical mechanisms to protect themselves from that environmental threat through a common strategy. Melanins in animals and flavonoids in plants are antioxidant pigments acting as free radical scavenging mechanisms. Both are phenol compounds constitutively synthesized and enhanced after exposure to UV rays, often conferring a red-brown-dark tissue pigmentation.Noteworthy, beside anti-oxidant scavenging activity, melanins and flavonoids have acquired secondary functions that, both in plants and animals, concern reproductions and fitness. Plants highly pigmented are more resistant to biotic and abiotic stresses. Darker wild vertebrates are generally more aggressive, sexually active and resistant to stress than lighter individuals. Flavonoids have been associated with signal attraction between flowers and insects and with plant-plant interaction. Melanin pigmentation has been proposed as trait in bird communication, acting as honest signals of quality.This review shows how the molecular mechanisms leading to tissue pigmentation have many functional analogies between plants and animals and how their origin lies in simpler organisms such as Cyanobacteria. Comparative studies between plant and animal kingdoms can reveal new insight of the antioxidant strategies in vivant.     

Evolution of class III homeodomain-leucine zipper genes in streptophytes

Land plants underwent tremendous evolutionary change following the divergence of the ancestral lineage from algal relatives. Several important developmental innovations appeared as the embryophyte clade diversified, leading to the appearance of new organs and tissue types. To understand how these changes came about, we need to identify the fundamental genetic developmental programs that are responsible for growth, patterning, and differentiation and describe how these programs were modified and elaborated through time to produce novel morphologies. Class III homeodomain-leucine zipper (class III HD-Zip) genes, identified in the model plant Arabidopsis thaliana, provide good candidates for basic land plant patterning genes. We show that these genes may have evolved in a common ancestor of land plants and their algal sister group and that the gene family has diversified as land plant lineages have diversified. Phylogenetic analysis, expression data from nonflowering lineages, and evidence from Arabidopsis and other flowering plants indicate that class III HD-Zip genes acquired new functions in sporophyte apical growth, vascular patterning and differentiation, and leaf development. Modification of expression patterns that accompanied diversification of class III HD-Zip genes likely played an important role in the evolution of land plant form.     

Major Evolutionary Trends in Hydrogen Isotope Fractionation of Vascular Plant Leaf Waxes

Hydrogen isotopic ratios of terrestrial plant leaf waxes (δD) have been widely used for paleoclimate reconstructions. However, underlying controls for the observed large variations in leaf wax δD values in different terrestrial vascular plants are still poorly understood, hampering quantitative paleoclimate interpretation. Here we report plant leaf wax and source water δD values from 102 plant species grown in a common environment (New York Botanic Garden), chosen to represent all the major lineages of terrestrial vascular plants and multiple origins of common plant growth forms. We found that leaf wax hydrogen isotope fractionation relative to plant source water is best explained by membership in particular lineages, rather than by growth forms as previously suggested. Monocots, and in particular one clade of grasses, display consistently greater hydrogen isotopic fractionation than all other vascular plants, whereas lycopods, representing the earlier-diverging vascular plant lineage, display the smallest fractionation. Data from greenhouse experiments and field samples suggest that the changing leaf wax hydrogen isotopic fractionation in different terrestrial vascular plants may be related to different strategies in allocating photosynthetic substrates for metabolic and biosynthetic functions, and potential leaf water isotopic differences.     

Effects of Short-Term Heat and Shade Treatments on Petal Colour of 'Baccara' Roses

Growth and pigmentation of ‘Baccara’ rose buds were followed. Petal elongation mainly occurred during a short period of time after the flowering shoot had stopped elongating. Approximately 90% of the flower pigments were synthesized during a short period lasting from the time the bud was 75% to the time it was 100% of its diameter at opening time. Petal growth continued after this period so that the pigments in the petal were “diluted”. Heat stress applied to whole plants or to flower buds only, or a short duration of low light intensities caused “blueing” of the petals when these conditions prevailed during the period of maximum pigmentation. Stress conditions prior to this period or following it, had no effect. We suggest that stress conditions such as high temperature or low light intensities reduce the availability of sugars. When this occurs at the time of maximum pigment production, a fall in the level of pigment occurs, which results in the “blueing” of the petals.     

Tissue specific effects of ommochrome pathway mutations in Drosophila melanogaster

The tissue-specific effects of 17 mutations affecting the synthesis of brown eye pigment (xanthommatin) have been investigated by combining them with chocolate and red cells, two mutations causing ectopic pigmentation of the Malpighian tubules and larval fat body (which normally only synthesize pigment precursors). The majority of mutations block the pigmentation of four organs; the normally pigmented eyes and ocelli, and ectopically pigmented tubules and fat body. They represent genes that would appear to be required for the normal operation of the pathway per se and are likely to encode structural proteins. Mutations at 5 loci affect pigmentation of a subset of organs: cd and po affect only the eyes and ocelli; kar affects the eyes, ocelli and fat body; car causes excretion of pigment from tubules; and z affects pigmentation of the eyes alone. Of these loci, only z has been shown to encode a regulatory protein and the role of the remaining four gene products is not clear. Two mutations affecting the red eye pigments (drosopterins), bw and mal, do not substantially perturb brown pigment synthesis in any of the four organs.     

Strategies to ameliorate abiotic stress-induced plant senescence

The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant responses to abiotic stresses. Both processes have an enormous negative global agro-economic impact and endanger food security worldwide. Premature plant senescence is the main cause of losses in grain filling and biomass yield due to leaf yellowing and deteriorated photosynthesis, and is also responsible for the losses resulting from the short shelf life of many vegetables and fruits. Under abiotic stress conditions the yield losses are often even greater. The primary challenge in agricultural sciences today is to develop technologies that will increase food production and sustainability of agriculture especially under environmentally limiting conditions. In this chapter, some of the mechanisms involved in abiotic stress-induced plant senescence are discussed. Recent studies have shown that crop yield and nutritional values can be altered as well as plant stress tolerance through manipulating the timing of senescence. It is often difficult to separate the effects of age-dependent senescence from stress-induced senescence since both share many biochemical processes and ultimately result in plant death. The focus of this review is on abiotic stress-induced senescence. Here, a number of the major approaches that have been developed to ameliorate some of the effects of abiotic stress-induced plant senescence are considered and discussed. Some approaches mimic the mechanisms already used by some plants and soil bacteria whereas others are based on development of new improved transgenic plants. While there may not be one simple strategy that can effectively decrease all losses of crop yield that accrue as a consequence of abiotic stress-induced plant senescence, some of the strategies that are discussed already show great promise.     

植物叶色形成调控机制研究进展

彩叶植物具有色彩鲜艳、观赏期长等特点,有助于提高城市绿化的观赏性.叶绿素、类胡萝卜素和花青素等天然色素的含量变化使叶片产生绿色、黄色、白色和紫红色等颜色,3种色素在光反应、响应生物和非生物胁迫中发挥重要作用.本文对影响叶绿素、类胡萝卜素和花青素生物合成途径遗传调控和外部环境因子综述,为解释叶片呈色机制提供理论基础.现有...     

Novel polyketide synthase from Nectria haematococca

We identified a polyketide synthase (PKS) gene, pksN, from a strain of Nectria haematococca by complementing a mutant unable to synthesize a red perithecial pigment. pksN encodes a 2,106-amino-acid polypeptide with conserved motifs characteristic of type I PKS enzymatic domains: beta-ketoacyl synthase, acyltransferase, duplicated acyl carrier proteins, and thioesterase. The pksN product groups with the Aspergillus nidulans WA-type PKSs involved in conidial pigmentation and melanin, bikaverin, and aflatoxin biosynthetic pathways. Inactivation of pksN did not cause any visible change in fungal growth, asexual sporulation, or ascospore formation, suggesting that it is involved in a specific developmental function. We propose that pksN encodes a novel PKS required for the perithecial red pigment biosynthesis.     

Endogenous and environmental factors influence 35S promoter methylation of a maize A1 gene construct in transgenic petunia and its colour phenotype

Summary 30000 transgenic petunia plants carrying a single copy of the maize A1 gene, encoding a dihydroflavonol reductase, which confers a salmon red flower colour phenotype on the petunia plant, were grown in a field test. During the growing season plants with flowers deviating from this salmon red colour, such as those showing white or variegated phenotypes and plants with flowers exhibiting only weak pigmentation were observed with varying frequencies. While four white flowering plants were shown at the molecular level to be mutants in which part of the A1 gene had been deleted, other white flowering plants, as well as 13 representative plants tested out of a total of 57 variegated individuals were not mutants but rather showed hypermethylation of the 35S promoter directing A1 gene expression. This was in contrast to the homogeneous fully red flowering plants in which no methylation of the 35S promoter was observed. While blossoms on plants flowering early in the season were predominantly red, later flowers on the same plants showed weaker coloration. Once again the reduction of the A1-specific phenotype correlated with the methylation of the 35S promoter. This variation in coloration seems to be dependent not only on exogenous but also on endogenous factors such as the age of the parental plant from which the seed was derived or the time at which crosses were made.     

Thiamine in plants: Aspects of its metabolism and functions

Thiamine diphosphate (vitamin B₁) plays a fundamental role as an enzymatic cofactor in universal metabolic pathways including glycolysis, the pentose phosphate pathway, and the tricarboxylic acid cycle. In addition, thiamine diphosphate has recently been shown to have functions other than as a cofactor in response to abiotic and biotic stress in plants. Recently, several steps of the plant thiamine biosynthetic pathway have been characterized, and a mechanism of feedback regulation of thiamine biosynthesis via riboswitch has been unraveled. This review focuses on these most recent advances made in our understanding of thiamine metabolism and functions in plants. Phenotypes of plant mutants affected in thiamine biosynthesis are described, and genomics, proteomics, and metabolomics data that have increased further our knowledge of plant thiamine metabolic pathways and functions are summarized. Aspects of thiamine metabolism such as catabolism, salvage, and transport in plants are discussed.