The Charophycean green algae as model systems to study plant cell walls and other evolutionary adaptations that gave rise to land plants

Emerging Research Topics in the Vibrionaceae and the Squid-Vibrio Symbiosis

The Vibrionaceae encompasses a cosmopolitan group that is mostly aquatic and possesses tremendous metabolic and genetic diversity. Given the importance of this taxon, it deserves continued and deeper research in a multitude of areas. This review outlines emerging topics of interest within the Vibrionaceae. Moreover, previously understudied research areas are highlighted that merit further exploration, including affiliations with marine plants (seagrasses), microbial predators, intracellular niches, and resistance to heavy metal toxicity. Agarases, phototrophy, phage shock protein response, and microbial experimental evolution are also fields discussed. The squid-Vibrio symbiosis is a stellar model system, which can be a useful guiding light on deeper expeditions and voyages traversing these "seas of interest". Where appropriate, the squid-Vibrio mutualism is mentioned in how it has or could facilitate the illumination of these various subjects. Additional research is warranted on the topics specified herein, since they have critical relevance for biomedical science, pharmaceuticals, and health care. There are also practical applications in agriculture, zymology, food science, and culinary use. The tractability of microbial experimental evolution is explained. Examples are given of how microbial selection studies can be used to examine the roles of chance, contingency, and determinism (natural selection) in shaping Earth's natural history.

An overview of microalgae biomass as a sustainable aquaculture feed ingredient: food security and circular economy

Sustainable management of natural resources is critical to food security. The shrimp feed and fishery sector is expanding rapidly, necessitating the development of alternative sustainable components. Several factors necessitate the exploration of a new source of environmentally friendly and nutrient-rich fish feed ingredients. Microalgal biomass has the potential to support the growth of fish and shrimp aquaculture for global food security in the bio-economy. Algal biorefineries must valorize the whole crop to develop a viable microalgae-based economy. Microalgae have the potential to replace fish meal and fish oil in aquaculture and ensure sustainability standards. Microalgae biomasses provide essential amino acids, valuable triglycerides such as lipids, vitamins, and pigments, making them suitable as nutritional supplements in livestock feed formulations. Fish and microalgae have similar nutritional profiles, and digestibility is a critical aspect of the aquafeed formulation. A highly digestible feed reduces production costs, feed waste, and the risk of eutrophication. Due to low input costs, low carbon footprint, wastewater treatment benefits, and carbon credits from industrial CO₂ conversion, microalgae-based fish and shrimp feeds have the potential to provide significant economic benefits. However, several challenges must be addressed before microalgal biomass and bioproducts may be used as fish feeds, including heavy metal bioaccumulation, poor algal biomass digestion, and antinutrient effects. Knowledge of biochemical composition is limited and diverse, and information on nutritional value is scattered or contradictory. This review article presents alternative approaches that could be used in aquaculture to make microalgal biomass a viable alternative to fish meal.

Environmental-biomechanical reciprocity and the evolution of plant material properties

Abiotic-biotic interactions have shaped organic evolution since life first began. Abiotic factors influence growth, survival, and reproductive success, whereas biotic responses to abiotic factors have changed the physical environment (and indeed created new environments). This reciprocity is well illustrated by land plants who begin and end their existence in the same location while growing in size over the course of years or even millennia, during which environment factors change over many orders of magnitude. A biomechanical, ecological, and evolutionary perspective reveals that plants are (i) composed of materials (cells and tissues) that function as cellular solids (i.e. materials composed of one or more solid and fluid phases); (ii) that have evolved greater rigidity (as a consequence of chemical and structural changes in their solid phases); (iii) allowing for increases in body size and (iv) permitting acclimation to more physiologically and ecologically diverse and challenging habitats; which (v) have profoundly altered biotic as well as abiotic environmental factors (e.g. the creation of soils, carbon sequestration, and water cycles). A critical component of this evolutionary innovation is the extent to which mechanical perturbations have shaped plant form and function and how form and function have shaped ecological dynamics over the course of evolution.

Aerobic and anaerobic removal of lead and mercury via calcium carbonate precipitation mediated by statistically optimized nitrate reductases

The nonbiodegradability nature of heavy metals renders them resident in food chain and subsequently, destructing the entire ecosystem. Therefore, this study aimed to employ nitrate reduction-driven calcium carbonate precipitation in remediation of lead and mercury aerobically and anaerobically by Proteus mirabilis 10B, for the first time. Initially, Plackett-Burman design was employed to screen of 16 independent variables for their significances on periplasmic (NAP) and membrane-bound (NAR) nitrate reductases. The levels for five significant variables and their interaction effects were further optimized by central composite design. The maximum activities of NAP and NAR recorded 2450 and 3050 U/mL by 2-fold enhancement, comparing with non-optimized medium. Under aerobic and anaerobic optimized remediation conditions, the changes in media chemistry revealed positive correlation among bacterial growth, nitrate reductase activity, pH, NO₃^- and NO₂^- consumption and removal of Ca²⁺, Pb²⁺ and Hg²⁺. Subsequently, the remediated precipitates were subjected to mineralogical analysis; energy dispersive X-ray patterns exhibited characteristic peaks of C, O and Ca in addition to Pb and Hg. Scanning electron microscope depicted the presence of bacterial imprints and protrusions on rough and smooth surface bioliths. However, X-ray diffraction indicated entrapment of PbCO₃, Pb₂O, CaPbO₃, Hg and Hg₂O in calcite lattice. Interestingly, such approach is feasible, efficient, cost-effective and ecofriendly for heavy metals remediation.

Xylans of Red and Green Algae: What Is Known about Their Structures and How They Are Synthesised?

Xylans with a variety of structures have been characterised in green algae, including chlorophytes (Chlorophyta) and charophytes (in the Streptophyta), and red algae (Rhodophyta). Substituted 1,4-β-d-xylans, similar to those in land plants (embryophytes), occur in the cell wall matrix of advanced orders of charophyte green algae. Small proportions of 1,4-β-d-xylans have also been found in the cell walls of some chlorophyte green algae and red algae but have not been well characterised. 1,3-β-d-Xylans occur as triple helices in microfibrils in the cell walls of chlorophyte algae in the order Bryopsidales and of red algae in the order Bangiales. 1,3;1,4-β-d-Xylans occur in the cell wall matrix of red algae in the orders Palmariales and Nemaliales. In the angiosperm Arabidopsis thaliana, the gene IRX10 encodes a xylan 1,4-β-d-xylosyltranferase (xylan synthase), and, when heterologously expressed, this protein catalysed the production of the backbone of 1,4-β-d-xylans. An orthologous gene from the charophyte green alga Klebsormidium flaccidum, when heterologously expressed, produced a similar protein that was also able to catalyse the production of the backbone of 1,4-β-d-xylans. Indeed, it is considered that land plant xylans evolved from xylans in ancestral charophyte green algae. However, nothing is known about the biosynthesis of the different xylans found in chlorophyte green algae and red algae. There is, thus, an urgent need to identify the genes and enzymes involved.

Does intrinsic light heterogeneity in Ricinus communis L. monospecific thickets drive species' population dynamics?

Ricinus communis L. colonizes heterogeneous urban landscapes as monospecific thickets. The ecological understanding on colonization success of R. communis population due to variable light availability is lacking. Therefore, to understand the effect of intrinsic light heterogeneity on species' population dynamics, R. communis populations exposed to variable light availability (low, intermediate, and high) were examined for performance strategies through estimation of key vegetative, eco-physiological, biochemical, and reproductive traits. Considerable variability existed in studied plant traits in response to available light. Individuals inhabiting high-light conditions exhibited high eco-physiological efficiency and reproductive performance that potentially confers population boom. Individuals exposed to low light showed poor performance in terms of eco-physiology and reproduction, which attribute to bust. However, individuals in intermediate light were observed to be indeterminate to light availability, potentially undergoing trait modulations with uncertainty of available light. Heterogeneous light availability potentially drives the boom and bust cycles in R. communis monospecific thickets. Such boom and bust cycles subsequently affect species' dominance, persistence, collapse, and/or resurgence as an aggressive colonizer in contrasting urban environments. The study fosters extensive monitoring of R. communis thickets to probe underlying mechanism(s) affecting expansions and/or collapses of colonizing populations.

Selenium mitigates cadmium-induced oxidative stress in tomato (Solanum lycopersicum L.) plants by modulating chlorophyll fluorescence, osmolyte accumulation, and antioxidant system

Pot experiments were conducted to investigate the role of selenium in alleviating cadmium stress in Solanum lycopersicum seedlings. Cadmium (150 mg L^-1) treatment caused a significant reduction in growth in terms of height and biomass accumulation and affected chlorophyll pigments, gas exchange parameters, and chlorophyll fluorescence. Selenium (10 μM) application mitigated the adverse effects of cadmium on growth, chlorophyll and carotenoid contents, leaf relative water content, and other physiological attributes. Lipid peroxidation and electrolyte leakage increased because of cadmium treatment and selenium-treated plants exhibited considerable reduction because of the decreased production of hydrogen peroxide in them. Cadmium-treated plants exhibited enhanced activity of antioxidant enzymes that protected cellular structures by neutralizing reactive free radicals. Supplementation of selenium to cadmium-treated plants (Cd + Se) further enhanced the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 19.69, 31.68, 33.14, and 54.47%, respectively. Osmolytes, including proline and glycine betaine, increased with selenium application, illustrating their role in improving the osmotic stability of S. lycopersicum under cadmium stress. More importantly, selenium application significantly reduced cadmium uptake. From these results, it is clear that application of selenium alleviates the negative effects of cadmium stress in S. lycopersicum through the modifications of osmolytes and antioxidant enzymes.

Antioxidant enzymes in chickpea colonized by Piriformospora indica participate in defense against the pathogen Botrytis cinerea

Piriformospora indica, a root endophytic fungus, promotes growth of the economically important chickpea plant (Cicer arietinum Linn.) and protects it against the pathogenic fungus Botrytis cinerea. Biomass and root development were found to be significantly improved in chickpea plants colonized with P. indica as compared to the plants grown without P. indica as well as from the plants infected with the B. cinerea. Our PCR analyses showed that gradual increase in the colonization of P. indica in the plants result in the inhibition of the colonization of B. cinerea. P. indica colonized plants showed increased antioxidant enzyme activities. Interestingly, there were pronounced decrease in the antioxidant enzyme activities in shoots infected with B. cinerea and colonized with P. indica in alternate and simultaneous mode as compared to plants infected with B. cinerea alone. We conclude that P. indica helps plants to overcome the disease load by enhancing antioxidant enzyme defense system. Our data suggest that, bio-protective action of P. indica might be mediated via systemic induction of antioxidant defense in the host plants.

Tolerance: the forgotten child of plant resistance

Plant resistance against insect herbivory has greatly focused on antibiosis, whereby the plant has a deleterious effect on the herbivore, and antixenosis, whereby the plant is able to direct the herbivore away from it. Although these two types of resistance may reduce injury and yield loss, they can produce selection pressures on insect herbivores that lead to pest resistance. Tolerance, on the other hand, is a more sustainable pest management strategy because it involves only a plant response and therefore does not cause evolution of resistance in target pest populations. Despite its attractive attributes, tolerance has been poorly studied and understood. In this critical, interpretive review, we discuss tolerance to insect herbivory and the biological and socioeconomic factors that have limited its use in plant resistance and integrated pest management. First, tolerance is difficult to identify, and the mechanisms conferring it are poorly understood. Second, the genetics of tolerance are mostly unknown. Third, several obstacles hinder the establishment of high-throughput phenotyping methods for large-scale screening of tolerance. Fourth, tolerance has received little attention from entomologists because, for most, their primary interest, research training, and funding opportunities are in mechanisms which affect pest biology, not plant biology. Fifth, the efforts of plant resistance are directed at controlling pest populations rather than managing plant stress. We conclude this paper by discussing future research and development activities.

Plant growth under water/salt stress: ROS production; antioxidants and significance of added potassium under such conditions

Plants are confronted with a variety of environmenmtal stresses resulting in enhanced production of ROS. Plants require a threshold level of ROS for vital functions and any change in their concentration alters the entire physiology of plant. Delicate balance of ROS is maintained by an efficient functioning of intriguing indigenous defence system called antioxidant system comprising enzymatic and non enzymatic components. Down regulation of antioxidant system leads to ROS induced oxidative stress causing damage to important cellular structures and hence anomalies in metabolism. Proper mineral nutrition, in addition to other agricultural practices, forms an important part for growth and hence the yield. Potassium (K) is a key macro-element regulating growth and development through alterations in physiological and biochemical attributes. K has been reported to result into accumulation of osmolytes and augmentation of antioxidant components in the plants exposed to water and salt stress. In the present review an effort has been made to revisit the old findings and the current advances in research regarding the role of optimal, suboptimal and deficient K soil status on growth under normal and stressful conditions. Effect of K deficiency and sufficiency is discussed and the information about the K mediated antioxidant regulation and plant response is highlighted.

Ricinus communis L. (castor bean) as a potential candidate for revegetating industrial waste contaminated sites in peri-urban Greater Hyderabad: remarks on seed oil

Ricinus communis L. (castor bean or castor oil plant) was found growing on metal-contaminated sites (4) of peri-urban Greater Hyderabad comprises of erstwhile industrial areas viz Bollaram, Patancheru, Bharatnagar, and Kattedan industrial areas. During 2013-2017, about 60 research papers have appeared focusing the role of castor bean in phytoremediation of co-contaminated soils, co-generation of biomaterials, and environmental cleanup, as bioenergy crop and sustainable development. The present study is focused on its use as a multipurpose phytoremediation crop for phytostabilization and revegetation of waste disposed peri-urban contaminated soils. To determine the plant tolerance level, metal accumulation, chlorophyll, protein, proline, lipid peroxidation, oil content, and soil properties were characterized. It was noticed that the castor plant and soils have high concentration of metals such as cadmium (Cd), lead (Pb), iron (Fe), manganese (Mn), and zinc (Zn). The soils have high phosphorous (P), adequate nitrogen (N), and low concentration of potassium (K). Iron (Fe) concentrations ranged from1672±50.91 to 2166±155.78 mg kg-1 in the soil. The trend of metal accumulation Fe>Zn>Mn>Pb>Cd was found in different plant parts at polluted sites. The translocation of Cd and Pb showed values more than one in industrial areas viz Bollaram, Kattedan, and Bharatnagar indicating the plants resistance to metal toxicity. Chlorophyll and protein content reduced while proline and malondialdehyde increased due to its tolerance level under metal exposure. The content of ricinoleic acid was higher, and the fatty acids composition of polluted areas was almost similar to that of the control area. Thus, R. communis L. can be employed for reclamation of heavy metal contaminated soils.

Plant regeneration through somatic embryogenesis and genome size analysis of Coriandrum sativum L

In the present study, an improved plant regeneration protocol via primary and secondary somatic embryogenesis was established in two Co-1 and Rajendra Swathi (RS) varieties of Coriandrum sativum L. Callus was induced from root explants on 2, 4-D (0.5-2.0 mg/l) supplemented MS. The addition of BA (0.2 mg/l) improved callus induction and proliferation response significantly. The maximum callus induction frequency was on 1.0 mg/l 2, 4-D and 0.2 mg/l BA added MS medium (77.5 % in Co-1 and 72.3 % in RS). The callus transformed into embryogenic callus on 2, 4-D added MS with maximum embryogenic frequency was on 1.0 mg/l. The granular embryogenic callus differentiated into globular embryos on induction medium, which later progressed to heart-, torpedo- and cotyledonary embryos on medium amended with 0.5 mg/l NAA and 0.2 mg/l BA. On an average, 2-3 secondary somatic embryos (SEs) were developed on mature primary SEs, which increased the total embryo numbers in culture. Histology and scanning electron microscopy (SEM) studies are presented for the origin, development of primary and secondary embryos in coriander. Later, these induced embryos converted into plantlets on 1.0 mg/l BA and 0.2 mg/l NAA-amended medium. The regenerated plantlets were cultured on 0.5 mg/l IBA added ½ MS for promotion of roots. The well-rooted plantlets were acclimatized and transferred to soil. The genetic stability of embryo-regenerated plant was analyzed by flow cytometry with optimized Pongamia pinnata as standard. The 2C DNA content of RS coriander variety was estimated to 5.1 pg; the primary and secondary somatic embryo-derived plants had 5.26 and 5.44 pg 2C DNA content, respectively. The regenerated plants were genetically stable, genome size similar to seed-germinated coriander plants.

Auxin Influx Carrier AUX1 Confers Acid Resistance for Arabidopsis Root Elongation Through the Regulation of Plasma Membrane H+-ATPase

The plant plasma membrane (PM) H+-ATPase regulates pH homeostasis and cell elongation in roots through the formation of an electrochemical H+ gradient across the PM and a decrease in apoplastic pH; however, the detailed signaling for the regulation of PM H+-ATPases remains unclear. Here, we show that an auxin influx carrier, AUXIN RESISTANT1 (AUX1), is required for the maintenance of PM H+-ATPase activity and proper root elongation. We isolated a low pH-hypersensitive 1 (loph1) mutant by a genetic screen of Arabidopsis thaliana on low pH agar plates. The loph1 mutant is a loss-of-function mutant of the AUX1 gene and exhibits a root growth retardation restricted to the low pH condition. The ATP hydrolysis and H+ extrusion activities of the PM H+-ATPase were reduced in loph1 roots. Furthermore, the phosphorylation of the penultimate threonine of the PM H+-ATPase was reduced in loph1 roots under both normal and low pH conditions without reduction of the amount of PM H+-ATPase. Expression of the DR5:GUS reporter gene and auxin-responsive genes suggested that endogenous auxin levels were lower in loph1 roots than in the wild type. The aux1-7 mutant roots also exhibited root growth retardation in the low pH condition like the loph1 roots. These results indicate that AUX1 positively regulates the PM H+-ATPase activity through maintenance of the auxin accumulation in root tips, and this process may serve to maintain root elongation especially under low pH conditions.

Transcriptome Profiling of the Green Alga Spirogyra pratensis (Charophyta) Suggests an Ancestral Role for Ethylene in Cell Wall Metabolism, Photosynthesis, and Abiotic Stress Responses

It is well known that ethylene regulates a diverse set of developmental and stress-related processes in angiosperms, yet its roles in early-diverging embryophytes and algae are poorly understood. Recently, it was shown that ethylene functions as a hormone in the charophyte green alga Spirogyra pratensis Since land plants evolved from charophytes, this implies conservation of ethylene as a hormone in green plants for at least 450 million years. However, the physiological role of ethylene in charophyte algae has remained unknown. To gain insight into ethylene responses in Spirogyra, we used mRNA sequencing to measure changes in gene expression over time in Spirogyra filaments in response to an ethylene treatment. Our analyses show that at the transcriptional level, ethylene predominantly regulates three processes in Spirogyra: (1) modification of the cell wall matrix by expansins and xyloglucan endotransglucosylases/hydrolases, (2) down-regulation of chlorophyll biosynthesis and photosynthesis, and (3) activation of abiotic stress responses. We confirmed that the photosynthetic capacity and chlorophyll content were reduced by an ethylene treatment and that several abiotic stress conditions could stimulate cell elongation in an ethylene-dependent manner. We also found that the Spirogyra transcriptome harbors only 10 ethylene-responsive transcription factor (ERF) homologs, several of which are regulated by ethylene. These results provide an initial understanding of the hormonal responses induced by ethylene in Spirogyra and help to reconstruct the role of ethylene in ancestral charophytes prior to the origin of land plants.

Micrasterias as a Model System in Plant Cell Biology

The unicellular freshwater alga Micrasterias denticulata is an exceptional organism due to its complex star-shaped, highly symmetric morphology and has thus attracted the interest of researchers for many decades. As a member of the Streptophyta, Micrasterias is not only genetically closely related to higher land plants but shares common features with them in many physiological and cell biological aspects. These facts, together with its considerable cell size of about 200 μm, its modest cultivation conditions and the uncomplicated accessibility particularly to any microscopic techniques, make Micrasterias a very well suited cell biological plant model system. The review focuses particularly on cell wall formation and composition, dictyosomal structure and function, cytoskeleton control of growth and morphogenesis as well as on ionic regulation and signal transduction. It has been also shown in the recent years that Micrasterias is a highly sensitive indicator for environmental stress impact such as heavy metals, high salinity, oxidative stress or starvation. Stress induced organelle degradation, autophagy, adaption and detoxification mechanisms have moved in the center of interest and have been investigated with modern microscopic techniques such as 3-D- and analytical electron microscopy as well as with biochemical, physiological and molecular approaches. This review is intended to summarize and discuss the most important results obtained in Micrasterias in the last 20 years and to compare the results to similar processes in higher plant cells.

Multiple functions of volatiles in flowers and leaves of Elsholtzia rugulosa (Lamiaceae) from southwestern China

Although the roles of volatile compounds have been examined separately in plant–herbivore or plant–pollinator interactions, few studies have focused on how plant scents can attract effective pollinators, repel ineffective pollinators, and defend against attacks by insect herbivores. We explored the functional significance of volatile compounds that impart a strong odor to Elsholtzia rugulosa, a shrub species in southwestern China. We monitored the pollinating honey bee Apis cerana, as well as two occasional visitors – Vespa velutina and a Bombus sp. – and an herbivorous beetle Oxycetonia jocunda. Behavior experiments using Y-tubes showed that honey bees were attracted primarily by floral scent while hornets and bumble bees were repelled by both the flowers and leaves. Analysis via gas chromatography-mass spectrometry revealed that these tissue types differed in their compositions and relative amounts of volatile compounds. When the plants were damaged, the average relative amounts of Elsholtzia ketone rapidly increased in the flowers and leaves. Furthermore, herbivorous beetles were strongly repelled by damaged tissues, suggesting a potential defense signaling function by these compounds. Our findings again demonstrate that scents have multiple functions in the interactions among plants and insects.

Charophytes: Evolutionary Giants and Emerging Model Organisms

Charophytes are the group of green algae whose ancestral lineage gave rise to land plants in what resulted in a profoundly transformative event in the natural history of the planet. Extant charophytes exhibit many features that are similar to those found in land plants and their relatively simple phenotypes make them efficacious organisms for the study of many fundamental biological phenomena. Several taxa including Micrasterias, Penium, Chara, and Coleochaete are valuable model organisms for the study of cell biology, development, physiology and ecology of plants. New and rapidly expanding molecular studies are increasing the use of charophytes that in turn, will dramatically enhance our understanding of the evolution of plants and the adaptations that allowed for survival on land. The Frontiers in Plant Science series on "Charophytes" provides an assortment of new research reports and reviews on charophytes and their emerging significance as model plants.

Abiotic Stress Tolerance of Charophyte Green Algae: New Challenges for Omics Techniques

Charophyte green algae are a paraphyletic group of freshwater and terrestrial green algae, comprising the classes of Chlorokybophyceae, Coleochaetophyceae, Klebsormidiophyceae, Zygnematophyceae, Mesostigmatophyceae, and Charo- phyceae. Zygnematophyceae (Conjugating green algae) are considered to be closest algal relatives to land plants (Embryophyta). Therefore, they are ideal model organisms for studying stress tolerance mechanisms connected with transition to land, one of the most important events in plant evolution and the Earth's history. In Zygnematophyceae, but also in Coleochaetophyceae, Chlorokybophyceae, and Klebsormidiophyceae terrestrial members are found which are frequently exposed to naturally occurring abiotic stress scenarios like desiccation, freezing and high photosynthetic active (PAR) as well as ultraviolet (UV) irradiation. Here, we summarize current knowledge about various stress tolerance mechanisms including insight provided by pioneer transcriptomic and proteomic studies. While formation of dormant spores is a typical strategy of freshwater classes, true terrestrial groups are stress tolerant in vegetative state. Aggregation of cells, flexible cell walls, mucilage production and accumulation of osmotically active compounds are the most common desiccation tolerance strategies. In addition, high photophysiological plasticity and accumulation of UV-screening compounds are important protective mechanisms in conditions with high irradiation. Now a shift from classical chemical analysis to next-generation genome sequencing, gene reconstruction and annotation, genome-scale molecular analysis using omics technologies followed by computer-assisted analysis will give new insights in a systems biology approach. For example, changes in transcriptome and role of phytohormone signaling in Klebsormidium during desiccation were recently described. Application of these modern approaches will deeply enhance our understanding of stress reactions in an unbiased non-targeted view in an evolutionary context.

Diversification of sterol methyltransferase enzymes in plants and a role for β-sitosterol in oriented cell plate formation and polarized growth

Phytosterols are classified into C24-ethylsterols and C24-methylsterols according to the different C24-alkylation levels conferred by two types of sterol methyltransferases (SMTs). The first type of SMT (SMT1) is widely conserved, whereas the second type (SMT2) has diverged in charophytes and land plants. The Arabidopsis smt2 smt3 mutant is defective in the SMT2 step, leading to deficiency in C24-ethylsterols while the C24-methylsterol pathway is unchanged. smt2 smt3 plants exhibit severe dwarfism and abnormal development throughout their life cycle, with irregular cell division followed by collapsed cell files. Preprophase bands are occasionally formed in perpendicular directions in adjacent cells, and abnormal phragmoplasts with mislocalized KNOLLE syntaxin and tubulin are observed. Defects in auxin-dependent processes are exemplified by mislocalizations of the PIN2 auxin efflux carrier due to disrupted cell division and failure to distribute PIN2 asymmetrically after cytokinesis. Although endocytosis of PIN2-GFP from the plasma membrane (PM) is apparently unaffected in smt2 smt3, strong inhibition of the endocytic recycling is associated with a remarkable reduction in the level of PIN2-GFP on the PM. Aberrant localization of the cytoplasmic linker associated protein (CLASP) and microtubules is implicated in the disrupted endocytic recycling in smt2 smt3. Exogenous C24-ethylsterols partially recover lateral root development and auxin distribution in smt2 smt3 roots. These results indicate that C24-ethylsterols play a crucial role in division plane determination, directional auxin transport, and polar growth. It is proposed that the divergence of SMT2 genes together with the ability to produce C24-ethylsterols were critical events to achieve polarized growth in the plant lineage.

The effect of drought on photosynthetic plasticity in Marrubium vulgare plants growing at low and high altitudes

Photosynthesis is a biological process most affected by water deficit. Plants have various photosynthetic mechanisms that are matched to specific climatic zones. We studied the photosynthetic plasticity of C3 plants at water deficit using ecotypes of Marrubium vulgare L. from high (2,200 m) and low (1,100 m) elevation sites in the Mishou-Dagh Mountains of Iran. Under experimental drought, high-altitude plants showed more tolerance to water stress based on most of the parameters studied as compared to the low-altitude plants. Increased tolerance in high-altitude plants was achieved by lower levels of daytime stomatal conductance (g s) and reduced damaging effect on maximal quantum yield of photosystem II (PSII) (F v /F m ) coupled with higher levels of carotenoids and non-photochemical quenching (NPQ). High-altitude plants exhibited higher water use efficiency (WUE) than that in low-altitude plants depending on the presence of thick leaves and the reduced daytime stomatal conductance. Additionally, we have studied the oscillation in H(+) content and diel gas exchange patterns to determine the occurrence of C3 or weak CAM (Crassulacean acid metabolism) in M. vulgare through 15 days drought stress. Under water-stressed conditions, low-altitude plants exhibited stomatal conductance and acid fluctuations characteristic of C3 photosynthesis, though high-altitude plants exhibited more pronounced increases in nocturnal acidity and phosphoenolpyruvate carboxylase (PEPC) activity, suggesting photosynthetic flexibility. These results indicated that the regulation of carotenoids, NPQ, stomatal conductance and diel patterns of CO2 exchange presented the larger differences among studied plants at different altitudes and seem to be the protecting mechanisms controlling the photosynthetic performance of M. vulgare plants under drought conditions.

Impacts of low level aflatoxin in feed and the use of modified yeast cell wall extract on growth and health of nursery pigs

This study was to investigate the effect of corn naturally contaminated with aflatoxins (AF) under the regulatory level on the growth performance and health of nursery pigs, and the efficiency of yeast cell wall based feed additive (YC) mainly composed of β-glucans and mannan oligosaccharide (MOS) (Integral A+, Alltech, Lexington, KY) in prevention of mycotoxicosis. Pigs (60 barrows and 60 gilts at 6.02 ± 0.83 kg BW) were randomly allotted to 4 treatments in a randomized complete block design based on a 2 × 2 factorial arrangement with 10 pens (5 barrow and 5 gilt pens) per treatment and 3 pigs per pen. Pigs were fed experimental diets for 5 wk. First factor was AF (0 or 20 µg/kg in feed) and the second factor was YC (0 or 2 g/kg in feed). Feed intake and body weight were measured weekly, and blood samples were used to measure blood cell counts, immunoglobulin G (IgG), tumor necrosis factor-a (TNF-a), oxidative damage status, and serological evaluation related to liver health. Aflatoxin decreased (P < 0.05) the number of platelet count (247.4 to 193.5 × 10³/µL), and it also tended to increase the level of albumin (P = 0.055, 3.46 to 3.63 g/dL), albumin:globulin ratio (P = 0.050, 2.09 to 2.37), and Ca (P = 0.080, 10.79 to 10.97 mg/dL). Yeast cell wall based feed additive increased (P < 0.05) ADG (493 to 524 g/d), and ADFI (796 to 846 g/d) of pigs whereas G:F was not affected, and it also tended to increase (P = 0.055) albumin level (3.46 to 3.63 g/dL). Interactions (P < 0.05) on hemoglobin, hematocrit, and platelet count indicated that YC further increased their levels when pigs were eating AF contaminated feed. Interactions (P < 0.05) on urea nitrogen and blood urea N to creatinine ratio indicated that YC further decreased their levels when feed were contaminated with AF. In conclusion, low level of 20 µg AF/kg under the regulatory level had minor effects on hematology without affecting growth performance, however the supplementation of 2 g/kg YC as a source of β-glucans and MOS in feed can improve feed intake and therefore the growth of pigs.

Influence of rhizobacterial volatiles on the root system architecture and the production and allocation of biomass in the model grass Brachypodium distachyon (L.) P. Beauv

BACKGROUND

Plant growth-promoting rhizobacteria are increasingly being seen as a way of complementing conventional inputs in agricultural systems. The effects on their host plants are diverse and include volatile-mediated growth enhancement. This study sought to assess the effects of bacterial volatiles on the biomass production and root system architecture of the model grass Brachypodium distachyon (L.) Beauv.

RESULTS

An in vitro experiment allowing plant-bacteria interaction throughout the gaseous phase without any physical contact was used to screen 19 bacterial strains for their growth-promotion ability over a 10-day co-cultivation period. Five groups of bacteria were defined and characterised based on their combined influence on biomass production and root system architecture. The observed effects ranged from unchanged to greatly increased biomass production coupled with increased root length and branching. Primary root length was increased only by the volatile compounds emitted by Enterobacter cloacae JM22 and Bacillus pumilus T4. Overall, the most significant results were obtained with Bacillus subtilis GB03, which induced an 81 % increase in total biomass, as well as enhancing total root length, total secondary root length and total adventitious root length by 88.5, 201.5 and 474.5 %, respectively.

CONCLUSIONS

This study is the first report on bacterial volatile-mediated growth promotion of a grass plant. Contrasting modulations of biomass production coupled with changes in root system architecture were observed. Most of the strains that increased total plant biomass also modulated adventitious root growth. Under our screening conditions, total biomass production was strongly correlated with the length and branching of the root system components, except for primary root length. An analysis of the emission kinetics of the bacterial volatile compounds is being undertaken and should lead to the identification of the compounds responsible for the observed growth-promotion effects. Within the context of the inherent characteristics of our in vitro system, this paper identifies the next critical experimental steps and discusses them from both a fundamental and an applied perspective.

Plant defence against aphids: the PAD4 signalling nexus

In Arabidopsis thaliana, PHYTOALEXIN DEFICIENT 4 (PAD4) functions as a key player in modulating defence against the phloem sap-feeding aphid Myzus persicae (Sülzer), more commonly known as the green peach aphid (GPA), an important pest of a wide variety of plants. PAD4 controls antibiosis and antixenosis against the GPA. In addition, PAD4 deters aphid feeding from sieve elements on Arabidopsis. In the past few years, substantial progress has been made in dissecting the role of PAD4 and its interaction with other signalling components in limiting aphid infestation. Several key genes/mechanisms involved in providing aphid resistance/susceptibility in Arabidopsis regulate the aphid infestation-stimulated expression of PAD4. Together, PAD4 and its interacting signalling partners provide a critical barrier to curtail GPA colonization of Arabidopsis.

Subcellular neuronal quasicrystals: Implications for consciousness

Neuron neurotransmitter receptors are in general pentameric. This enables them to form pentagonal components in biological quasicrystals (similar to mathematical aperiodic tilings). As quasicrystals have been proposed to require quantum effects to exist this might introduce such effects as a component of neurotransmission and thus consciousness. Microtubules may play a role in the clustering of the receptors into quasicrystals, thus modulating their function and may even form quasicrystals themselves. Other quaiscrystals in neurons are potentially formed by water, cholera toxin complexes, and the cytoskeletal components actin and ankyrin.

Aluminum ions alter the function of non-specific phospholipase C through the changes in plasma membrane physical properties

The first indication of the aluminum (Al) toxicity in plants growing in acidic soils is the cessation of root growth, but the detailed mechanism of Al effect is unknown. Here we examined the impact of Al stress on the activity of non-specific phospholipase C (NPC) in the connection with the processes related to the plasma membrane using fluorescently labeled phosphatidylcholine. We observed a rapid and significant decrease of labeled diacylglycerol (DAG), product of NPC activity, in Arabidopsis seedlings treated with AlCl₃. Interestingly, an application of the membrane fluidizer, benzyl alcohol, restored the level of DAG during Al treatment. Our observations suggest that the activity of NPC is affected by Al-induced changes in plasma membrane physical properties.

Penium margaritaceum as a model organism for cell wall analysis of expanding plant cells

The growth of a plant cell encompasses a complex set of subcellular components interacting in a highly coordinated fashion. Ultimately, these activities create specific cell wall structural domains that regulate the prime force of expansion, internally generated turgor pressure. The precise organization of the polymeric networks of the cell wall around the protoplast also contributes to the direction of growth, the shape of the cell, and the proper positioning of the cell in a tissue. In essence, plant cell expansion represents the foundation of development. Most studies of plant cell expansion have focused primarily upon late divergent multicellular land plants and specialized cell types (e.g., pollen tubes, root hairs). Here, we describe a unicellular green alga, Penium margaritaceum (Penium), which can serve as a valuable model organism for understanding cell expansion and the underlying mechanics of the cell wall in a single plant cell.

The GRAS gene family in pine: transcript expression patterns associated with the maturation-related decline of competence to form adventitious roots

BACKGROUND

Adventitious rooting is an organogenic process by which roots are induced from differentiated cells other than those specified to develop roots. In forest tree species, age and maturation are barriers to adventitious root formation by stem cuttings. The mechanisms behind the respecification of fully differentiated progenitor cells, which underlies adventitious root formation, are unknown.

RESULTS

Here, the GRAS gene family in pine is characterized and the expression of a subset of these genes during adventitious rooting is reported. Comparative analyses of protein structures showed that pine GRAS members are conserved compared with their relatives in angiosperms. Relatively high GRAS mRNA levels were measured in non-differentiated proliferating embryogenic cultures and during embryo development. The mRNA levels of putative GRAS family transcription factors, including Pinus radiata's SCARECROW (SCR), PrSCR, and SCARECROW-LIKE (SCL) 6, PrSCL6, were significantly reduced or non-existent in adult tissues that no longer had the capacity to form adventitious roots, but were maintained or induced after the reprogramming of adult cells in rooting-competent tissues. A subset of genes, SHORT-ROOT (PrSHR), PrSCL1, PrSCL2, PrSCL10 and PrSCL12, was also expressed in an auxin-, age- or developmental-dependent manner during adventitious root formation.

CONCLUSIONS

The GRAS family of pine has been characterized by analyzing protein structures, phylogenetic relationships, conserved motifs and gene expression patterns. Individual genes within each group have acquired different and specialized functions, some of which could be related to the competence and reprogramming of adult cells to form adventitious roots.

Can adaptive modulation of traits to urban environments facilitate Ricinus communis L. invasiveness?

This paper addresses the phenotypic variation among Ricinus communis L. populations in four urban habitat types (road verges, garbage dumps, construction debris, and natural area) in Delhi, India, by evaluating important traits such as plant height, basal circumference, seeds per plant, seed size, seed weight, specific leaf area, and reproductive index. An important biochemical marker, proline, considered as a good plant performance indicator under stress was also quantified in leaves of R. communis to evaluate its response in different habitats. Interestingly, the species showed significant variation in plant height, specific leaf area, seed size, seed weight, and leaf proline content in different habitat types. Leaf proline content was positively related to plant height, specific leaf area, and seed size while negatively related to the total number of seeds/plant. Interestingly, reproductive index, calculated as a ratio of the total number of seeds to the plant height also showed a negative relation with leaf proline content. Results indicated that R. communis exhibits adaptive modulation of growth, reproductive traits, and leaf proline content in various urban habitats which contributes to invasiveness, range expansion, and establishment of the species. The study also gives evidence of how morphological and physiological traits could directly affect invasiveness of R. communis.

Biomass and RRR-α-tocopherol production in Stichococcus bacillaris strain siva2011 in a balloon bioreactor

Background

Green microalgae represent a renewable natural source of vitamin E. Its most bioactive form is the naturally occurring RRR-α-tocopherol which is biosynthesized in photosynthetic organisms as a single stereoisomer. It is noteworthy that the natural and synthetic α-tocopherols are different biomolecular entities. This article focuses on RRR-α-tocopherol production in Stichococcus bacillaris strain siva2011 biomass in a bioreactor culture with methyl jasmonate (MeJa) elicitor. Additionally, a nonlinear mathematical model was used to quantitatively scale-up and predict the biomass production in a 20 L balloon bioreactor with dual variables such as time and volume.

Results

Approximately 0.6 mg/g dry weight (DW) of RRR-α-tocopherol was enhanced in S. bacillaris strain siva2011 biomass with the MeJa 50 μL/L for 24 hrs elicitations when compared to the control. The R² value from the nonlinear model was enhanced up to 95% when compared to the linear model which significantly improved the accuracy for estimating S. bacillaris strain siva2011 biomass production in a balloon bioreactor.

Conclusions

S. bacillaris strain siva2011 is a new green microalga which biosynthesizes significant amounts of RRR-α-tocopherol. Systematically validated dual variable empirical data should provide key insights to multivariable or fourth order modeling for algal biomass scale-up. This bioprocess engineering should provide valuable information for industrial production of RRR-α-tocopherol from green cells.

Oxidized fatty acids as inter-kingdom signaling molecules

Oxylipins or oxidized fatty acids are a group of molecules found to play a role in signaling in many different cell types. These fatty acid derivatives have ancient evolutionary origins as signaling molecules and are ideal candidates for inter-kingdom communication. This review discusses examples of the ability of organisms from different kingdoms to “listen” and respond to oxylipin signals during interactions. The interactions that will be looked at are signaling between animals and plants; between animals and fungi; between animals and bacteria and between plants and fungi. This will aid in understanding these interactions, which often have implications in ecology, agriculture as well as human and animal health.

Understanding plant defence responses against herbivore attacks: an essential first step towards the development of sustainable resistance against pests

Plant-herbivore relationships are complex interactions encompassing elaborate networks of molecules, signals and strategies used to overcome defences developed by each other. Herbivores use multiple feeding strategies to obtain nutrients from host plants. In turn, plants respond by triggering defence mechanisms to inhibit, block or modify the metabolism of the pest. As part of these defences, herbivore-challenged plants emit volatiles to attract natural enemies and warn neighbouring plants of the imminent threat. In response, herbivores develop a variety of strategies to suppress plant-induced protection. Our understanding of the plant-herbivore interphase is limited, although recent molecular approaches have revealed the participation of a battery of genes, proteins and volatile metabolites in attack-defence processes. This review describes the intricate and dynamic defence systems governing plant-herbivore interactions by examining the diverse strategies plants employ to deny phytophagous arthropods the ability to breach newly developed mechanisms of plant resistance. A cornerstone of this understanding is the use of transgenic tools to unravel the complex networks that control these interactions.

Extensive chromosomal reshuffling drives evolution of virulence in an asexual pathogen

Sexual recombination drives genetic diversity in eukaryotic genomes and fosters adaptation to novel environmental challenges. Although strictly asexual microorganisms are often considered as evolutionary dead ends, they comprise many devastating plant pathogens. Presently, it remains unknown how such asexual pathogens generate the genetic variation that is required for quick adaptation and evolution in the arms race with their hosts. Here, we show that extensive chromosomal rearrangements in the strictly asexual plant pathogenic fungus Verticillium dahliae establish highly dynamic lineage-specific (LS) genomic regions that act as a source for genetic variation to mediate aggressiveness. We show that such LS regions are greatly enriched for in planta-expressed effector genes encoding secreted proteins that enable host colonization. The LS regions occur at the flanks of chromosomal breakpoints and are enriched for retrotransposons and other repetitive sequence elements. Our results suggest that asexual pathogens may evolve by prompting chromosomal rearrangements, enabling rapid development of novel effector genes. Likely, chromosomal reshuffling can act as a general mechanism for adaptation in asexually propagating organisms.

MKRN expression pattern during embryonic and post-embryonic organogenesis in rice (Oryza sativa L. var. Nipponbare)

Rice MKRN is a member of the makorin RING finger protein gene (MKRN) family, which encodes a protein with a characteristic array of zinc-finger motifs conserved in various eukaryotes. Using non-radioactive in situ hybridization, we investigated the spatio-temporal gene expression pattern of rice MKRN during embryogenesis, imbibition, seminal and lateral root development of Oryza sativa L. var. Nipponbare. MKRN expression was ubiquitous during early organogenesis in the embryo along the apical-basal and radial axes. The expression of MKRN decreased during embryonic organ elongation and maturation compared to early embryogenesis, but increased again during imbibition. Tissue-specific and position-dependent MKRN expression was found during embryonic and post-embryonic root and shoot development. Meristematic cells ubiquitously expressed MKRN transcripts, while differentiating cells showed a gradual reduction and termination of MKRN expression. Interestingly, during post-germination MKRN expression was prominent and continued in the metabolically active, differentiated companion cells of the phloem. The differential expression pattern was observed both in the differentiating and differentiated cells. Also, MKRN was expressed in the various developmental stages of the lateral root primordia and the cells surrounding them. Expression of MKRN was also observed after periclinal division of the presumptive pericycle founder cells. The MKRN expression pattern during development of various growth stages suggests an important role of makorin RING finger protein gene (MKRN) in embryonic and post-embryonic organogenesis in both apical-basal and radial developmental axes of rice.

UniVIO: a multiple omics database with hormonome and transcriptome data from rice

Plant hormones play important roles as signaling molecules in the regulation of growth and development by controlling the expression of downstream genes. Since the hormone signaling system represents a complex network involving functional cross-talk through the mutual regulation of signaling and metabolism, a comprehensive and integrative analysis of plant hormone concentrations and gene expression is important for a deeper understanding of hormone actions. We have developed a database named Uniformed Viewer for Integrated Omics (UniVIO: http://univio.psc.riken.jp/), which displays hormone-metabolome (hormonome) and transcriptome data in a single formatted (uniformed) heat map. At the present time, hormonome and transcriptome data obtained from 14 organ parts of rice plants at the reproductive stage and seedling shoots of three gibberellin signaling mutants are included in the database. The hormone concentration and gene expression data can be searched by substance name, probe ID, gene locus ID or gene description. A correlation search function has been implemented to enable users to obtain information of correlated substance accumulation and gene expression. In the correlation search, calculation method, range of correlation coefficient and plant samples can be selected freely.

Pectate chemistry links cell expansion to wall deposition in Chara corallina

Pectate (polygalacturonic acid) acts as a chelator to bind calcium and form cross-links that hold adjacent pectate polymers and thus plant cell walls together. When under tension from turgor pressure in the cell, the cross-links appear to distort and weaken. New pectate supplied by the cytoplasm is undistorted and removes wall calcium preferentially from the weakened bonds, loosening the wall and accelerating cell expansion. The new pectate now containing the removed calcium can bind to the wall, strengthening it and linking expansion to wall deposition. But new calcium needs to be added as well to replenish the calcium lost from the vacated wall pectate.  A recent report demonstrated that growth was disrupted if new calcium was unavailable.  The present addendum highlights this conclusion by reviewing an experiment from before the chelation chemistry was understood. Using cell wall labeling, a direct link appeared between wall expansion and wall deposition. Together, these experiments support the concept that newly supplied pectate has growth activity on its way to deposition in the wall. Growth rate is thus controlled by signals affecting the rate of pectate release. After release, the coordination of expansion and deposition arises naturally from chelation chemistry when polymers are under tension from turgor pressure. 

microRNAs targeting DEAD-box helicases are involved in salinity stress response in rice (Oryza sativa L.)

BACKGROUND

Rice (Oryza sativa L.), one of the most important food crop in the world, is considered to be a salt-sensitive crop. Excess levels of salt adversely affect all the major metabolic activities, including cell wall damage, cytoplasmic lysis and genomic stability. In order to cope with salt stress, plants have evolved high degrees of developmental plasticity, including adaptation via cascades of molecular networks and changes in gene expression profiles. Posttranscriptional regulation, through the activity of microRNAs, also plays an important role in the plant response to salinity conditions. MicroRNAs are small endogenous RNAs that modulate gene expression and are involved in the most essential physiological processes, including plant development and adaptation to environmental changes.

RESULTS

In the present study, we investigated the expression profiles of osa-MIR414, osa-MIR408 and osa-MIR164e along with their targeted genes, under salinity stress conditions in wild type and transgenic rice plants ectopically expressing the PDH45 (Pea DNA Helicase) gene. The present miRNAs were predicted to target the OsABP (ATP-Binding Protein), OsDSHCT (DOB1/SK12/helY-like DEAD-box Helicase) and OsDBH (DEAD-Box Helicase) genes, included in the DEAD-box helicase family. An in silico characterization of the proteins was performed and the miRNAs predicted targets were validated by RLM-5'RACE. The qRT-PCR analysis showed that the OsABP, OsDBH and OsDSHCT genes were up-regulated in response to 100 and 200 mM NaCl treatments. The present study also highlighted an increased accumulation of the gene transcripts in wild type plants, with the exception of the OsABP mRNA which showed the highest level (15.1-fold change compared to control) in the transgenic plants treated with 200 mM NaCl. Salinity treatments also affected the expression of osa-MIR414, osa-MIR164e and osa-MIR408, found to be significantly down-regulated, although the changes in miRNA expression were limited.

CONCLUSIONS

Osa-MIR414, osa-MIR164e and osa-MIR408 were experimentally validated for the first time in plants as targeting the OsABP, OsDBH and OsDSHCT genes. Our data showed that that the genes were up-regulated and the miRNAs were down-regulated in relation to salt stress. The negative correlation between the miRNAs and their targets was proven.

Calcium promotes activity and confers heat stability on plant peroxidases

In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca(2+) ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca(2+) concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca(2+) binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance.

Calcium promotes activity and confers heat stability on plant peroxidases

In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca(2+) ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca(2+) concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca(2+) binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance.

The Cell Walls of Green Algae: A Journey through Evolution and Diversity

The green algae represent a large group of morphologically diverse photosynthetic eukaryotes that occupy virtually every photic habitat on the planet. The extracellular coverings of green algae including cell walls are also diverse. A recent surge of research in green algal cell walls fueled by new emerging technologies has revealed new and critical insight concerning these coverings. For example, the late divergent taxa of the Charophycean green algae possess cell walls containing assemblages of polymers with notable similarity to the cellulose, pectins, hemicelluloses, arabinogalactan proteins (AGPs), extensin, and lignin present in embryophyte walls. Ulvophycean seaweeds have cell wall components whose most abundant fibrillar constituents may change from cellulose to β-mannans to β-xylans and during different life cycle phases. Likewise, these algae produce complex sulfated polysaccharides, AGPs, and extensin. Chlorophycean green algae produce a wide array of walls ranging from cellulose-pectin complexes to ones made of hydroxyproline-rich glycoproteins. Larger and more detailed surveys of the green algal taxa including incorporation of emerging genomic and transcriptomic data are required in order to more fully resolve evolutionary trends within the green algae and in relationship with higher plants as well as potential applications of wall components in the food and pharmaceutical industries.

Piriformospora indica, a cultivable plant-growth-promoting root endophyte

Piriformospora indica (Hymenomycetes, Basidiomycota) is a newly described cultivable endophyte that colonizes roots. Inoculation with the fungus and application of fungal culture filtrate promotes plant growth and biomass production. Due to its ease of culture, this fungus provides a model organism for the study of beneficial plant-microbe interactions and a new tool for improving plant production systems.