Showing papers in "New Phytologist in 2009"

Fungal endophytes: diversity and functional roles.

Abstract: Summary 1 Summary All plants in natural ecosystems appear to be symbiotic with fungal endophytes. This highly diverse group of fungi can have profound impacts on plant communities through increasing fitness by conferring abiotic and biotic stress tolerance, increasing biomass and decreasing water consumption, or decreasing fitness by altering resource allocation. Despite more than 100 yr of research resulting in thousands of journal articles, the ecological significance of these fungi remains poorly characterized. Historically, two endophytic groups (clavicipitaceous (C) and nonclavicipitaceous (NC)) have been discriminated based on phylogeny and life history traits. Here, we show that NC-endophytes represent three distinct functional groups based on host colonization and transmission, in planta biodiversity and fitness benefits conferred to hosts. Using this framework, we contrast the life histories, interactions with hosts and potential roles in plant ecophysiology of C- and NC-endophytes, and highlight several key questions for future work in endophyte biology.

Causes and consequences of variation in leaf mass per area (LMA): a meta-analysis.

Abstract: Here, we analysed a wide range of literature data on the leaf dry mass per unit area (LMA). In nature, LMA varies more than 100-fold among species. Part of this variation (c. 35%) can be ascribed to differences between functional groups, with evergreen species having the highest LMA, but most of the variation is within groups or biomes. When grown in the same controlled environment, leaf succulents and woody evergreen, perennial or slow-growing species have inherently high LMA. Within most of the functional groups studied, high-LMA species show higher leaf tissue densities. However, differences between evergreen and deciduous species result from larger volumes per area (thickness). Response curves constructed from experiments under controlled conditions showed that LMA varied strongly with light, temperature and submergence, moderately with CO2 concentration and nutrient and water stress, and marginally under most other conditions. Functional groups differed in the plasticity of LMA to these gradients. The physiological regulation is still unclear, but the consequences of variation in LMA and the suite of traits interconnected with it are strong. This trait complex is an important factor determining the fitness of species in their environment and affects various ecosystem processes.

Biofortification of crops with seven mineral elements often lacking in human diets--iron, zinc, copper, calcium, magnesium, selenium and iodine.

Abstract: Summary The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of ‘promoter’ substances, such as ascorbate, β-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of ‘antinutrients’, such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.

Arsenic uptake and metabolism in plants.

Abstract: Arsenic (As) is an element that is nonessential for and toxic to plants. Arsenic contamination in the environment occurs in many regions, and, depending on environmental factors, its accumulation in food crops may pose a health risk to humans.Recent progress in understanding the mechanisms of As uptake and metabolism in plants is reviewed here. Arsenate is taken up by phosphate transporters. A number of the aquaporin nodulin26-like intrinsic proteins (NIPs) are able to transport arsenite,the predominant form of As in reducing environments. In rice (Oryza sativa), arsenite uptake shares the highly efficient silicon (Si) pathway of entry to root cells and efflux towards the xylem. In root cells arsenate is rapidly reduced to arsenite, which is effluxed to the external medium, complexed by thiol peptides or translocated to shoots. One type of arsenate reductase has been identified, but its in planta functions remain to be investigated. Some fern species in the Pteridaceae family are able to hyperaccumulate As in above-ground tissues. Hyperaccumulation appears to involve enhanced arsenate uptake, decreased arsenite-thiol complexation and arsenite efflux to the external medium, greatly enhanced xylem translocation of arsenite, and vacuolar sequestration of arsenite in fronds. Current knowledge gaps and future research directions are also identified.

Uptake of organic nitrogen by plants.

Abstract: Languishing for many years in the shadow of plant inorganic nitrogen (N) nutrition research, studies of organic N uptake have attracted increased attention during the last decade. The capacity of plants to acquire organic N, demonstrated in laboratory and field settings, has thereby been well established. Even so, the ecological significance of organic N uptake for plant N nutrition is still a matter of discussion. Several lines of evidence suggest that plants growing in various ecosystems may access organic N species. Many soils display amino acid concentrations similar to, or higher than, those of inorganic N, mainly as a result of rapid hydrolysis of soil proteins. Transporters mediating amino acid uptake have been identified both in mycorrhizal fungi and in plant roots. Studies of endogenous metabolism of absorbed amino acids suggest that L- but not D-enantiomers are efficiently utilized. Dual labelled amino acids supplied to soil have provided strong evidence for plant uptake of organic N in the field but have failed to provide information on the quantitative importance of this process. Thus, direct evidence that organic N contributes significantly to plant N nutrition is still lacking. Recent progress in our understanding of the mechanisms underlying plant organic N uptake may open new avenues for the exploration of this subject.

454 Pyrosequencing analyses of forest soils reveal an unexpectedly high fungal diversity

Abstract: Summary • Soil fungi play a major role in ecological and biogeochemical processes in forests. Little is known, however, about the structure and richness of different fungal communities and the distribution of functional ecological groups (pathogens, saprobes and symbionts). • Here, we assessed the fungal diversity in six different forest soils using tagencoded 454 pyrosequencing of the nuclear ribosomal internal transcribed spacer1 (ITS-1). No less than 166 350 ITS reads were obtained from all samples. In each forest soil sample (4 g), approximately 30 000 reads were recovered, corresponding to around 1000 molecular operational taxonomic units. • Most operational taxonomic units (81%) belonged to the Dikarya subkingdom (Ascomycota and Basidiomycota). Richness, abundance and taxonomic analyses identified the Agaricomycetes as the dominant fungal class. The ITS-1 sequences (73%) analysed corresponded to only 26 taxa. The most abundant operational taxonomic units showed the highest sequence similarity to Ceratobasidium sp., Cryptococcus podzolicus, Lactarius sp. and Scleroderma sp. • This study validates the effectiveness of high-throughput 454 sequencing technology for the survey of soil fungal diversity. The large proportion of unidentified sequences, however, calls for curated sequence databases. The use of pyrosequencing on soil samples will accelerate the study of the spatiotemporal dynamics of fungal communities in forest ecosystems.

Molecular mechanisms of metal hyperaccumulation in plants

Abstract: Contents Summary 759 I. Hyperaccumulation: the phenomenon 759 II. Macroevolution of hyperaccumulation 760 III. Microevolution of hyperaccumulation: variation within hyperaccumulator species 760 IV. Genetic analysis of trace metal accumulation and tolerance 761 V. Mechanisms of trace metal accumulation 762 VI. General discussion and research perspectives 769 Acknowledgements 772 References 772 Summary Metal hyperaccumulator plants accumulate and detoxify extraordinarily high concentrations of metal ions in their shoots. Metal hyperaccumulation is a fascinating phenomenon, which has interested scientists for over a century. Hyperaccumulators constitute an exceptional biological material for understanding mechanisms regulating plant metal homeostasis as well as plant adaptation to extreme metallic environments. Our understanding of metal hyperaccumulation physiology has recently increased as a result of the development of molecular tools. This review presents key aspects of our current understanding of plant metal – in particular cadmium (Cd), nickel (Ni) and zinc (Zn) – hyperaccumulation.

Global patterns of foliar nitrogen isotopes and their relationships with climate, mycorrhizal fungi, foliar nutrient concentrations, and nitrogen availability

Abstract: Ratios of nitrogen (N) isotopes in leaves could elucidate underlying patterns of N cycling across ecological gradients. To better understand global-scale patterns of N cycling, we compiled data on foliar N isotope ratios (delta(15)N), foliar N concentrations, mycorrhizal type and climate for over 11,000 plants worldwide. Arbuscular mycorrhizal, ectomycorrhizal, and ericoid mycorrhizal plants were depleted in foliar delta(15)N by 2 per thousand, 3.2 per thousand, 5.9 per thousand, respectively, relative to nonmycorrhizal plants. Foliar delta(15)N increased with decreasing mean annual precipitation and with increasing mean annual temperature (MAT) across sites with MAT >or= -0.5 degrees C, but was invariant with MAT across sites with MAT < -0.5 degrees C. In independent landscape-level to regional-level studies, foliar delta(15)N increased with increasing N availability; at the global scale, foliar delta(15)N increased with increasing foliar N concentrations and decreasing foliar phosphorus (P) concentrations. Together, these results suggest that warm, dry ecosystems have the highest N availability, while plants with high N concentrations, on average, occupy sites with higher N availability than plants with low N concentrations. Global-scale comparisons of other components of the N cycle are still required for better mechanistic understanding of the determinants of variation in foliar delta(15)N and ultimately global patterns in N cycling.

Gene duplication and evolutionary novelty in plants.

Abstract: Duplication is a prominent feature of plant genomic architecture. This has led many researchers to speculate that gene duplication may have played an important role in the evolution of phenotypic novelty within plants. Until recently, however, it was difficult to make this connection. We are now beginning to understand how duplication has contributed to adaptive evolution in plants. In this review we introduce the sources of gene duplication and predictions of the various fates of duplicates. We also highlight several recent and pertinent examples from the literature. These examples demonstrate the importance of the functional characteristics of genes and the source of duplication in influencing evolutionary outcome.

Shaping the calcium signature.

Abstract: In numerous plant signal transduction pathways, Ca2+ is a versatile second messenger which controls the activation of many downstream actions in response to various stimuli. There is strong evidence to indicate that information encoded within these stimulus-induced Ca2+ oscillations can provide signalling specificity. Such Ca2+ signals, or 'Ca2+ signatures', are generated in the cytosol, and in noncytosolic locations including the nucleus and chloroplast, through the coordinated action of Ca2+ influx and efflux pathways. An increased understanding of the functions and regulation of these various Ca2+ transporters has improved our appreciation of the role these transporters play in specifically shaping the Ca2+ signatures. Here we review the evidence which indicates that Ca2+ channel, Ca2+-ATPase and Ca2+ exchanger isoforms can indeed modulate specific Ca2+ signatures in response to an individual signal.

Dissecting iron deficiency-induced proton extrusion in Arabidopsis roots

Abstract: Here, we have analysed the H(+)-ATPase-mediated extrusion of protons across the plasma membrane (PM) of rhizodermic cells, a process that is inducible by iron (Fe) deficiency and thought to serve in the mobilization of sparingly soluble Fe sources The induction and function of Fe-responsive PM H(+)-ATPases in Arabidopsis roots was investigated by gene expression analysis and by using mutants defective in the expression or function of one of the isogenes In addition, the expression of the most responsive isogenes was investigated in natural Arabidopsis accessions that have been selected for their in vivo proton extrusion activity Our data suggest that the rhizosphere acidification in response to Fe deficiency is chiefly mediated by AHA2, while AHA1 functions as a housekeeping isoform The aha7 knock-out mutant plants showed a reduced frequency of root hairs, suggesting an involvement of AHA7 in the differentiation of rhizodermic cells Acidification capacity varied among Arabidopsis accessions and was associated with a high induction of AHA2 and IRT1, a high relative growth rate and a shoot-root ratio that was unaffected by the external Fe supply An effective regulation of the Fe-responsive genes and a stable shoot-root ratio may represent important characteristics for the Fe uptake efficiency

Biogenic volatile organic compounds in the Earth system

Abstract: Biogenic volatile organic compounds produced by plants are involved in plant growth, development, reproduction and defence. They also function as communication media within plant communities, between plants and between plants and insects. Because of the high chemical reactivity of many of these compounds, coupled with their large mass emission rates from vegetation into the atmosphere, they have significant effects on the chemical composition and physical characteristics of the atmosphere. Hence, biogenic volatile organic compounds mediate the relationship between the biosphere and the atmosphere. Alteration of this relationship by anthropogenically driven changes to the environment, including global climate change, may perturb these interactions and may lead to adverse and hard-to-predict consequences for the Earth system.New Phytologist (2009) 183: 27-51doi: 10.1111/j.1469-8137.2009.02859.x.

Large-scale parallel 454 sequencing reveals host ecological group specificity of arbuscular mycorrhizal fungi in a boreonemoral forest.

Abstract: * Knowledge of the diversity of arbuscular mycorrhizal fungi (AMF) in natural ecosystems is a major bottleneck in mycorrhizal ecology. Here, we aimed to apply 454 sequencing--providing a new level of descriptive power--to assess the AMF diversity in a boreonemoral forest. * 454 sequencing reads of the small subunit ribosomal RNA (SSU rRNA) gene of Glomeromycota were assigned to sequence groups by blast searches against a custom-made annotated sequence database. * We detected 47 AMF taxa in the roots of 10 plant species in a 10 x 10 m plot, which is almost the same as the number of plant species in the whole studied forest. There was a significant difference between AMF communities in the roots of forest specialist plant species and in the roots of habitat generalist plant species. Forest plant species hosted 22 specialist AMF taxa, and the generalist plants shared all but one AMF taxon with forest plants, including globally distributed generalist fungi. These AMF taxa that have been globally recorded only in forest ecosystems were significantly over-represented in the roots of forest plant species. * Our findings suggest that partner specificity in AM symbiosis may occur at the level of ecological groups, rather than at the species level, of both plant and fungal partners.

Arbuscular mycorrhizal fungi can transfer substantial amounts of nitrogen to their host plant from organic material

Abstract: Nitrogen (N) capture by arbuscular mycorrhizal (AM) fungi from organic material is a recently discovered phenomenon. This study investigated the ability of two Glomus species to transfer N from organic material to host plants and examined whether the ability to capture N is related to fungal hyphal growth. Experimental microcosms had two compartments; these contained either a single plant of Plantago lanceolata inoculated with Glomus hoi or Glomus intraradices, or a patch of dried shoot material labelled with (15)N and (13)carbon (C). In one treatment, hyphae, but not roots, were allowed access to the patch; in the other treatment, access by both hyphae and roots was prevented. When allowed, fungi proliferated in the patch and captured N but not C, although G. intraradices transferred more N than G. hoi to the plant. Plants colonized with G. intraradices had a higher concentration of N than controls. Up to one-third of the patch N was captured by the AM fungi and transferred to the plant, while c. 20% of plant N may have been patch derived. These findings indicate that uptake from organic N could be important in AM symbiosis for both plant and fungal partners and that some AM fungi may acquire inorganic N from organic sources.

The importance of cytosolic glutamine synthetase in nitrogen assimilation and recycling

Abstract: Glutamine synthetase assimilates ammonium into amino acids, thus it is a key enzyme for nitrogen metabolism. The cytosolic isoenzymes of glutamine synthetase assimilate ammonium derived from primary nitrogen uptake and from various internal nitrogen recycling pathways. In this way, cytosolic glutamine synthetase is crucial for the remobilization of protein-derived nitrogen. Cytosolic glutamine synthetase is encoded by a small family of genes that are well conserved across plant species. Members of the cytosolic glutamine synthetase gene family are regulated in response to plant nitrogen status, as well as to environmental cues, such as nitrogen availability and biotic/abiotic stresses. The complex regulation of cytosolic glutamine synthetase at the transcriptional to post-translational levels is key to the establishment of a specific physiological role for each isoenzyme. The diverse physiological roles of cytosolic glutamine synthetase isoenzymes are important in relation to current agricultural and ecological issues.

Massively parallel 454 sequencing indicates hyperdiverse fungal communities in temperate Quercus macrocarpa phyllosphere

Abstract: * This study targeted the fungal communities in the phyllosphere of Quercus macrocarpa and compared the fungal species richness, diversity and community composition among trees located within and outside a small urban center using recently developed 454 sequencing and DNA tagging. * The results indicate that the fungal phyllosphere communities are extremely diverse and strongly dominated by ascomycetes, with Microsphaeropsis [two Operational Taxonomic Units (OTUs); 23.6%], Alternaria (six OTUs; 16.1%), Epicoccum (one OTU; 6.0%) and Erysiphe (two OTUs; 5.9%) as the most abundant genera. * Although the sequencing effort averaged 1000 reads per tree and detected nearly 700 distinct molecular OTUs at 95% internal transcribed spacer 1 similarity, the richness of the hyperdiverse phyllosphere communities could not be reliably estimated as nearly one-half of the molecular OTUs were singletons. * The fungal communities within and outside the urban center differed in richness and diversity, which were lower within the urban development. The two land-use types contained communities that were distinct and more than 10% of the molecular OTUs differed in their frequency.

Rhizosphere bacteria containing 1-aminocyclopropane-1-carboxylate deaminase increase yield of plants grown in drying soil via both local and systemic hormone signalling

Abstract: Decreased soil water availability can stimulate production of the plant hormone ethylene and inhibit plant growth. Strategies aimed at decreasing stress ethylene evolution might attenuate its negative effects. An environmentally benign (nonchemical) method of modifying crop ethylene relations - soil inoculation with a natural root-associated bacterium Variovorax paradoxus 5C-2 (containing the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase that degrades the ethylene precursor ACC), was assessed with pea (Pisum sativum) plants grown in drying soil. Inoculation with V. paradoxus 5C-2, but not with a transposome mutant with massively decreased ACC deaminase activity, improved growth, yield and water-use efficiency of droughted peas. Systemic effects of V. paradoxus 5C-2 included an amplified soil drying-induced increase of xylem abscisic acid (ABA) concentration, but an attenuated soil drying-induced increase of xylem ACC concentration. A local bacterial effect was increased nodulation by symbiotic nitrogen-fixing bacteria, which prevented a drought-induced decrease in nodulation and seed nitrogen content. Successfully deploying a single bacterial gene in the rhizosphere increased yield and nutritive value of plants grown in drying soil, via both local and systemic hormone signalling. Such bacteria may provide an easily realized, economic means of sustaining crop yields and using irrigation water more efficiently in dryland agriculture.

DNA-based species level detection of Glomeromycota: one PCR primer set for all arbuscular mycorrhizal fungi.

Abstract: Summary • At present, molecular ecological studies of arbuscular mycorrhizal fungi (AMF) are only possible above species level when targeting entire communities. To improve molecular species characterization and to allow species level community analyses in the field, a set of newly designed AMF specific PCR primers was successfully tested.  Nuclear rDNA fragments from diverse phylogenetic AMF lineages were sequenced and analysed to design four primer mixtures, each targeting one binding site in the small subunit (SSU) or large subunit (LSU) rDNA. To allow species resolution, they span a fragment covering the partial SSU, whole internal transcribed spacer (ITS) rDNA region and partial LSU.  The new primers are suitable for specifically amplifying AMF rDNA from material that may be contaminated by other organisms (e.g., samples from pot cultures or the field), characterizing the diversity of AMF species from field samples, and amplifying a SSU-ITS-LSU fragment that allows phylogenetic analyses with species level resolution.  The PCR primers can be used to monitor entire AMF field communities, based on a single rDNA marker region. Their application will improve the base for deep sequencing approaches; moreover, they can be efficiently used as DNA barcoding primers.

The CBL–CIPK Ca2+-decoding signaling network: function and perspectives

Abstract: Contents Summary 517 I. Introduction 517 II. Comparative genomics of the CBL–CIPK signaling network 518 III. Structural features and functional principles of CBLs and CIPKs 521 IV. Functions and targets of CBL–CIPK complexes 523 Conclusions and perspectives 525 Acknowledgements 526 References 526 Summary Calcium serves as a versatile messenger in many adaptation and developmental processes in plants. Cellular calcium signals are detected and transmitted by calcium-binding proteins functioning as sensor molecules. The family of calcineurin B-like (CBL) proteins represents a unique group of calcium sensors and contributes to the decoding of calcium transients by interacting with and regulating the family of CBL-interacting protein kinases (CIPKs). In higher plants, CBL proteins and CIPKs form a complex signaling network that allows for flexible but specific signal–response coupling during environmental adaptation reactions. This review presents novel findings concerning the evolution of this signaling network and key insights into the physiological function of CBL–CIPK complexes. These aspects will be presented and discussed in the context of emerging functional principles governing efficient and specific information processing in this signaling system.

HMA P-type ATPases are the major mechanism for root-to-shoot Cd translocation in Arabidopsis thaliana.

Abstract: The Zn/Cd-transporting ATPases, HMA2 and HMA4, essential for root-to-shoot Zn translocation, are also able to transport Cd. Phytochelatins (PCs) are a major mechanism of Cd detoxification through the sequestration of PC-Cd complexes in vacuoles. The roles of HMA2 and HMA4 in root-to-shoot Cd translocation and Cd tolerance were investigated in the PC-deficient, cad1-3 mutant and CAD1 backgrounds. Six lines, with all possible combinations of hma2, hma4 and cad1 mutations, were constructed. The lines were tested for Cd-sensitivity on agar medium, and radioactive (109)Cd was used to measure Cd uptake and translocation from root to shoot over periods of up to 6 d. In hma4 and hma2,hma4, but not hma2, root-to-shoot Cd translocation was decreased to about 60 and 2%, respectively, of that in the wild-type. Cd sensitivity increased approximately twofold in the hma2,hma4 mutant in both CAD1 and cad1 backgrounds. PC deficiency resulted in an increase in shoot Cd concentrations. The near-complete abolition of root-to-shoot Cd translocation resulting from the loss of function of HMA2 and HMA4 demonstrates they are the major mechanism for Cd translocation in Arabidopsis thaliana.

Darwin's beautiful contrivances: evolutionary and functional evidence for floral adaptation

Abstract: Contents Summary 530 I. Introduction 530 II. The process of floral and inflorescence adaptation 532 III. Experimental studies of flowers as adaptations 538 IV. Floral diversification: microevolution writ large? 539 V. Concluding comments 541 Acknowledgements 542 References 542 Summary Although not ‘a professed botanist’, Charles Darwin made seminal contributions to understanding of floral and inflorescence function while seeking evidence of adaptation by natural selection. This review considers the legacy of Darwin's ideas from three perspectives. First, we examine the process of floral and inflorescence adaptation by surveying studies of phenotypic selection, heritability and selection responses. Despite widespread phenotypic and genetic capacity for natural selection, only one-third of estimates indicate phenotypic selection. Second, we evaluate experimental studies of floral and inflorescence function and find that they usually demonstrate that reproductive traits represent adaptations. Finally, we consider the role of adaptation in floral diversification. Despite different diversification modes (coevolution, divergent use of the same pollen vector, pollinator shifts), evidence of pollination ecotypes and phylogenetic patterns suggests that adaptation commonly contributes to floral diversity. Thus, this review reveals a contrast between the inconsistent occurrence of phenotypic selection and convincing experimental and comparative evidence that floral traits are adaptations. Rather than rejecting Darwin's hypotheses about floral evolution, this contrast suggests that the tempo of creative selection varies, with strong, consistent selection during episodes of diversification, but relatively weak and inconsistent selection during longer, ‘normal’ periods of relative phenotypic stasis.

Hydraulic adjustment of Scots pine across Europe

Abstract: Summary • The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits.  Traits measured included wood density, radial growth, xylem anatomy, sapwoodand leaf-specific hydraulic conductivity (KS and KL), vulnerability to embolism, leaf-to-sapwood area ratio (AL : AS), needle carbon isotope discrimination (Δ 13 C) and nitrogen content, and specific leaf area.  Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for AL : AS, KL and Δ 13 C. Shoot radial growth and AL : AS declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species.  The adjustment of Scots pine’s hydraulic system to local climatic conditions occurred primarily through modifications of AL : AS and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.

Agriculture and the new challenges for photosynthesis research.

Abstract: A rising human population and changing patterns of land use mean that world food production rates will need to be increased by at least 50% by 2050, a massive rise in harvestable yield per hectare of the major crops such as rice (Oryza sativa) and wheat (Triticum aestivum). Combinations of breeding for improved morphology-related traits such as harvest index and increased inputs of water and fertilizer, which have sustained yield increases since the 1960s, will be neither sufficient nor sustainable. An important limiting factor will be the capacity to produce sufficient biomass during favourable growing periods. Here we analyse this problem in the context of increasing the efficiency of conversion of solar energy into biomass, that is, leaf and canopy photosynthesis. Focussing on crops carrying out C3 photosynthesis, we analyse the evidence for 'losses' in the process of conversion of solar energy into crop biomass and we explore novel mechanisms of improving biomass production rates, which have arisen from recent research into the fundamental primary processes of photosynthesis and carbohydrate metabolism. We show that there are several lines of evidence that these processes are not fully optimized for maximum yield. We put forward the hypothesis that the chloroplast itself should be given greater prominence as a sensor, processor and integrator of highly variable environmental signals to allow a more efficient transduction of energy supply into biomass production.

Fitness costs associated with evolved herbicide resistance alleles in plants.

Abstract: Predictions based on evolutionary theory suggest that the adaptive value of evolved herbicide resistance alleles may be compromised by the existence of fitness costs. There have been many studies quantifying the fitness costs associated with novel herbicide resistance alleles, reflecting the importance of fitness costs in determining the evolutionary dynamics of resistance. However, many of these studies have incorrectly defined resistance or used inappropriate plant material and methods to measure fitness. This review has two major objectives. First, to propose a methodological framework that establishes experimental criteria to unequivocally evaluate fitness costs. Second, to present a comprehensive analysis of the literature on fitness costs associated with herbicide resistance alleles. This analysis reveals unquestionable evidence that some herbicide resistance alleles are associated with pleiotropic effects that result in plant fitness costs. Observed costs are evident from herbicide resistance-endowing amino acid substitutions in proteins involved in amino acid, fatty acid, auxin and cellulose biosynthesis, as well as enzymes involved in herbicide metabolism. However, these resistance fitness costs are not universal and their expression depends on particular plant alleles and mutations. The findings of this review are discussed within the context of the plant defence trade-off theory and herbicide resistance evolution.

More than a carbon economy: nutrient trade and ecological sustainability in facultative arbuscular mycorrhizal symbioses

Abstract: Summary Symbiosis is well recognized as a major force in plant ecology and evolution. However, there is considerable uncertainty about the functional, ecological and evolutionary benefits of the very widespread facultative arbuscular mycorrhizal (AM) associations, in which the plants can grow and reproduce whether or not they are colonized by AM fungi. Here we address the significance of new research findings that are overturning conventional views that facultative AM associations can be likened to parasitic fungus–plant associations. Specifically, we address the occurrence and importance of phosphate uptake via AM fungi that does not result in increases in total phosphorus (P) uptake or in plant growth, and possible signalling between AM fungi and plants that can result in plant growth depressions even when fungal colonization remains very low. We conclude that, depending on the individual AM fungi that are present, the role of facultative AM associations in the field, especially in relation to plant competition, may be much more subtle than has been previously envisaged.

Microbiological control of soil‐borne phytopathogenic fungi with special emphasis on wilt‐inducing Fusarium oxysporum

Abstract: Contents Summary 529 I. Biological control of plant diseases: state of the art 530 II. Main modes of action of biological control agents 530 III. The protective strains of F. oxysporum: an unexplored model 532 IV. Future directions for the study of the protective capacity of strains of F. oxysporum 539 V. How to make biological control successful in the field? 540 References 541 Summary Plant diseases induced by soil-borne plant pathogens are among the most difficult to control. In the absence of effective chemical control methods, there is renewed interest in biological control based on application of populations of antagonistic micro-organisms. In addition to Pseudomonas spp. and Trichoderma spp., which are the two most widely studied groups of biological control agents, the protective strains of Fusarium oxysporum represent an original model. These protective strains of F. oxysporum can be used to control wilt induced by pathogenic strains of the same species. Exploring the mechanisms involved in the protective capability of these strains is not only necessary for their development as commercial biocontrol agents but raises many basic questions related to the determinism of pathogenicity versus biocontrol capacity in the F. oxysporum species complex. In this paper, current knowledge regarding the interaction between the plant and the protective strains is reviewed in comparison with interactions between the plant and pathogenic strains. The success of biological control depends not only on plant–microbial interactions but also on the ecological fitness of the biological control agents.

Improving plant stress tolerance and yield production: is the tonoplast aquaporin SlTIP2;2 a key to isohydric to anisohydric conversion?

Abstract: Summary • Anisohydric plants are thought to be more drought tolerant than isohydric plants. However, the molecular mechanism determining whether the plant water potential during the day remains constant or not regardless of the evaporative demand (isohydric vs anisohydric plant) is not known. • Here, it was hypothesized that aquaporins take part in this molecular mechanism determining the plant isohydric threshold. Using computational mining a key tonoplast aquaporin, tonoplast intrinsic protein 2;2 (SlTIP2;2), was selected within the large multifunctional gene family of tomato (Solanum lycopersicum) aquaporins based on its induction in response to abiotic stresses. SlTIP2;2-transformed plants (TOM-SlTIP2;2) were compared with controls in physiological assays at cellular and whole-plant levels. • Constitutive expression of SlTIP2;2 increased the osmotic water permeability of the cell and whole-plant transpiration. Under drought, these plants transpired more and for longer periods than control plants, reaching a lower relative water content, a behavior characterizing anisohydric plants. In 3-yr consecutive commercial glasshouse trials, TOM-SlTIP2;2 showed significant increases in fruit yield, harvest index and plant mass relative to the control under both normal and water-stress conditions. • In conclusion, it is proposed that the regulation mechanism controlling tonoplast water permeability might have a role in determining the whole-plant ishohydric threshold, and thus its abiotic stress tolerance.

Jasmonates act with salicylic acid to confer basal thermotolerance in Arabidopsis thaliana

Abstract: * The cpr5-1 Arabidopsis thaliana mutant exhibits constitutive activation of salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signalling pathways and displays enhanced tolerance of heat stress (HS). * cpr5-1 crossed with jar1-1 (a JA-amino acid synthetase) was compromised in basal thermotolerance, as were the mutants opr3 (mutated in OPDA reductase3) and coi1-1 (affected in an E3 ubiquitin ligase F-box; a key JA-signalling component). In addition, heating wild-type Arabidopsis led to the accumulation of a range of jasmonates: JA, 12-oxophytodienoic acid (OPDA) and a JA-isoleucine (JA-Ile) conjugate. Exogenous application of methyl jasmonate protected wild-type Arabidopsis from HS. * Ethylene was rapidly produced during HS, with levels being modulated by both JA and SA. By contrast, the ethylene mutant ein2-1 conferred greater thermotolerance. * These data suggest that JA acts with SA, conferring basal thermotolerance while ET may act to promote cell death.

Genome-wide reprogramming of regulatory networks, transport, cell wall and membrane biogenesis during arbuscular mycorrhizal symbiosis in Lotus japonicus.

Abstract: Summary • Arbuscular mycorrhizas (AMs) contribute significantly to soil nutrient uptake in plants. As a consequence of the fungal colonization and of the deep reorganization shown by arbusculated cells, important impacts on root transcriptome are expected. • An Affymetrix GeneChip with 50 000 probe-sets and real-time RT-PCR allowed us to detect transcriptional changes triggered in Lotus japonicus by the AM fungus Gigaspora margarita, when arbuscules are at their maximum (28 d postinoculation (dpi)). An early time (4 dpi) was selected to differentiate genes potentially involved in signaling and/or in colonization of outer tissues. • A large number (75 out of 558) of mycorrhiza-induced genes code for proteins involved in protein turnover, membrane dynamics and cell wall synthesis, while many others are involved in transport (47) or transcription (24). Induction of a subset (24 genes) of these was tested and confirmed by qRT-PCR, and transcript location in arbusculated cells was demonstrated for seven genes using laser-dissected cells. • When compared with previously published papers, the transcript profiles indicate the presence of a core set of responsive genes (25) that seem to be conserved irrespective of the symbiotic partner identity.

'Glomus intraradices DAOM197198', a model fungus in arbuscular mycorrhiza research, is not Glomus intraradices.

Abstract: Summary • Glomus intraradices-like fungi are the most intensely studied arbuscular mycorrhizal (AM) fungi. However, there are several AM fungi named as G. intraradices that may not be conspecific. Therefore, the hypothesis was tested that DAOM197198 and similar AM fungi, such as BEG195, correspond to the type of G. intraradices. • The G. intraradices isotype material, a descendant (INVAM FL208) of the type culture, and a morphologically corresponding AM fungus (MUCL49410) isolated from the type locality were studied and compared with several cultures of DAOM197198 and BEG195. • Phylogenetic analyses of the partial small subunit (SSU), complete internal transcribed spacer (ITS) and partial large subunit (LSU) nuclear rDNA regions revealed two clades, one including G. intraradices FL208 and MUCL49410, the other containing DAOM197198 and BEG195. • The two clades were clearly separated by sequence analyses, despite the high intraspecific and intrasporal ITS region sequence divergence of up to > 23%. We conclude that the AM fungi with the identifiers DAOM197198 and BEG195 are not G. intraradices, but fall in a clade that contains the recently described species G. irregulare.