Auxin modulates the enhanced development of root hairs in Arabidopsis thaliana (L.) Heynh. under elevated CO(2)

Action mechanisms of small microbial volatile compounds in plants

Microorganisms communicate with plants by exchanging chemical signals throughout the phytosphere. Before direct contact with plants occurs, beneficial microorganisms emit a plethora of volatile compounds that promote plant growth and photosynthesis as well as developmental, metabolic, transcriptional, and proteomic changes in plants. These compounds can also induce systemic drought tolerance and improve water and nutrient acquisition. Recent studies have shown that this capacity is not restricted to beneficial microbes; it also extends to phytopathogens. Plant responses to microbial volatile compounds have frequently been associated with volatile organic compounds with molecular masses ranging between ~ 45Da and 300Da. However, microorganisms also release a limited number of volatile compounds with molecular masses of less than ~45Da that react with proteins and/or act as signaling molecules. Some of these compounds promote photosynthesis and growth when exogenously applied in low concentrations. Recently, evidence has shown that small volatile compounds are important determinants of plant responses to microbial volatile emissions. However, the regulatory mechanisms involved in these responses remain poorly understood. This review summarizes current knowledge of biochemical and molecular mechanisms involved in plant growth, development, and metabolic responses to small microbial volatile compounds.

Regulation of Phytohormones on the Growth and Development of Plant Root Hair

The tubular-shaped unicellular extensions of plant epidermal cells known as root hairs are important components of plant roots and play crucial roles in absorbing nutrients and water and in responding to stress. The growth and development of root hair include, mainly, fate determination of root hair cells, root hair initiation, and root hair elongation. Phytohormones play important regulatory roles as signal molecules in the growth and development of root hair. In this review, we describe the regulatory roles of auxin, ethylene (ETH), jasmonate (JA), abscisic acid (ABA), gibberellin (GA), strigolactone (SL), cytokinin (CK), and brassinosteroid (BR) in the growth and development of plant root hairs. Auxin, ETH, and CK play positive regulation while BR plays negative regulation in the fate determination of root hair cells; Auxin, ETH, JA, CK, and ABA play positive regulation while BR plays negative regulation in the root hair initiation; Auxin, ETH, CK, and JA play positive regulation while BR, GA, and ABA play negative regulation in the root hair elongation. Phytohormones regulate root hair growth and development mainly by regulating transcription of root hair associated genes, including WEREWOLF (WER), GLABRA2 (GL2), CAPRICE (CPC), and HAIR DEFECTIVE 6 (RHD6). Auxin and ETH play vital roles in this regulation, with JA, ABA, SL, and BR interacting with auxin and ETH to regulate further the growth and development of root hairs.

Multi-level gene regulatory network models to understand complex mechanisms underlying plant development

Patterning in plant development is the emergent outcome of the feedback-based interplay between tissue-coupled intracellular regulatory networks and physicochemical fields. This interplay gives rise to dynamics that evolve on a wide spectrum of spatiotemporal scales. This imposes important challenges for computational approaches to model the dynamics of plant development. These challenges are being tackled in recent times by computational and mathematical advances that have made progress in the modelling of regulatory networks, as well as in approaches to couple the latter to physicochemical fields. Efforts in this direction are fundamental to identify the dynamical constraints that emerge from non-cellular autonomous activity in cell-fate decisions and patterning, and requires an understanding of how multi-level and multi-scale processes are coupled. Here, we discuss the use of multi-level modeling and simulation tools for the study of multicellular systems, with emphasis on plants. As illustrative examples, we discuss recent works elucidating the mechanisms that underlie patterning in the root meristem of Arabidopsis thaliana, and in plant responses to environmental conditions.

Volatile compounds other than CO2 emitted by different microorganisms promote distinct posttranscriptionally regulated responses in plants

A "box-in-box" cocultivation system was used to investigate plant responses to microbial volatile compounds (VCs) and to evaluate the contributions of organic and inorganic VCs (VOCs and VICs, respectively) to these responses. Arabidopsis plants were exposed to VCs emitted by adjacent Alternaria alternata and Penicillium aurantiogriseum cultures, with and without charcoal filtration. No VOCs were detected in the headspace of growth chambers containing fungal cultures with charcoal filters. However, these growth chambers exhibited elevated CO₂ and bioactive CO and NO headspace concentrations. Independently of charcoal filtration, VCs from both fungal phytopathogens promoted growth and distinct developmental changes. Plants cultured at CO₂ levels observed in growth boxes containing fungal cultures were identical to those cultured at ambient CO₂ . Plants exposed to charcoal-filtered fungal VCs, nonfiltered VCs, or superelevated CO₂ levels exhibited transcriptional changes resembling those induced by increased irradiance. Thus, in the "box-in-box" system, (a) fungal VICs other than CO₂ and/or VOCs not detected by our analytical systems strongly influence the plants' responses to fungal VCs, (b) different microorganisms release VCs with distinct action potentials, (c) transcriptional changes in VC-exposed plants are mainly due to enhanced photosynthesis signaling, and (d) regulation of some plant responses to fungal VCs is primarily posttranscriptional.

Elevated CO2-induced production of nitric oxide differentially modulates nitrate assimilation and root growth of wheat seedlings in a nitrate dose-dependent manner

Wheat is a major staple food crop worldwide contributing approximately 20% of total protein consumed by mankind. The nitrogen and protein concentration of wheat crop and grain often decline as a result of exposure of the crop to elevated CO₂ (EC). The changes in nitrogen (N) assimilation, root system architecture, and nitric oxide (NO)-mediated N signaling and expression of genes involved in N assimilation and high affinity nitrate uptake were examined in response to different nitrate levels and EC in wheat. Activity of enzyme nitrate reductase (NRA) was downregulated under EC both in leaf and root tissues. Plants grown under EC displayed enhanced production of NO and more so when nitrate supply was high. Based on exogenous supply of NO, inhibitors of NO production, and NO scavenger, regulatory role of NO on EC mediated changes in root morphology and NRA was revealed. The enhanced NO production under EC and high N levels negatively regulated the transcript abundance of NR and high affinity nitrate transporters (HATS).

Elevated carbon dioxide and drought modulate physiology and storage-root development in sweet potato by regulating microRNAs

Elevated CO₂ along with drought is a serious global threat to crop productivity. Therefore, understanding the molecular mechanisms plants use to protect these stresses is the key for plant growth and development. In this study, we mimicked natural stress conditions under a controlled Soil-Plant-Atmosphere-Research (SPAR) system and provided the evidence for how miRNAs regulate target genes under elevated CO₂ and drought conditions. Significant physiological and biomass data supported the effective utilization of source-sink (leaf to root) under elevated CO₂. Additionally, elevated CO₂ partially rescued the effect of drought on total biomass. We identified both known and novel miRNAs differentially expressed during drought, CO₂, and combined stress, along with putative targets. A total of 32 conserved miRNAs belonged to 23 miRNA families, and 25 novel miRNAs were identified by deep sequencing. Using the existing sweet potato genome database and stringent analyses, a total of 42 and 22 potential target genes were predicted for the conserved and novel miRNAs, respectively. These target genes are involved in drought response, hormone signaling, photosynthesis, carbon fixation, sucrose and starch metabolism, etc. Gene ontology and KEGG ontology functional enrichment revealed that these miRNAs might target transcription factors (MYB, TCP, NAC), hormone signaling regulators (ARF, AP2/ERF), cold and drought factors (corA), carbon metabolism (ATP synthase, fructose-1,6-bisphosphate), and photosynthesis (photosystem I and II complex units). Our study is the first report identifying targets of miRNAs under elevated CO₂ levels and could support the molecular mechanisms under elevated CO₂ in sweet potato and other crops in the future.

Natural variation among Arabidopsis thaliana accessions in tolerance to high magnesium supply

High magnesium (Mg2+) in some extreme serpentine soils or semi-arid regions is an important factor affecting crop growth and development. Specific loci that form the genetic framework underlying high Mg2+ homeostasis, however, are not well understood. By using GWA mapping on 388 accessions of Arabidopsis thaliana selected from a worldwide collection and genotyped at approximately 250,00 SNPs, we successfully identified 109 and 74 putative genetic regions associated in nutrient traits under normal (1,000 µM) and high Mg2+ (10,000 µM), respectively. Above 90% SNPs associated with nutrients including Mg2+ and only two SNPs shared between normal and high Mg2+. A single strong peak of SNPs associated with Ca concentration corresponding to candidate gene At1g60420 ARABIDOPSIS NUCLEOREDOXIN (AtNRX1) under high Mg2+ was further determined. Compared with wildtype, mutants of Atnrx1-1 and Atnrx1-2 supplied with high Mg2+ had higher Ca concentrations in the plant, and higher cytosolic Ca2+ concentrations during root elongation, as well as higher fresh weight and lateral-root number. This suggests that AtNRX1 was a critical gene negatively regulating Ca uptake under high Mg2+ conditions. The discovery could help to breed/select crops that can adapt to high-Mg2+ soils such as serpentine soils (high ratio of Mg2+: Ca2+) or Mars soil with high levels of magnesium sulfate.

Increasing carbon availability stimulates growth and secondary metabolites via modulation of phytohormones in winter wheat

Phytohormones play important roles in plant acclimation to changes in environmental conditions. However, their role in whole-plant regulation of growth and secondary metabolite production under increasing atmospheric CO2 concentrations ([CO2]) is uncertain but crucially important for understanding plant responses to abiotic stresses. We grew winter wheat (Triticum aestivum) under three [CO2] (170, 390, and 680 ppm) over 10 weeks, and measured gas exchange, relative growth rate (RGR), soluble sugars, secondary metabolites, and phytohormones including abscisic acid (ABA), auxin (IAA), jasmonic acid (JA), and salicylic acid (SA) at the whole-plant level. Our results show that, at the whole-plant level, RGR positively correlated with IAA but not ABA, and secondary metabolites positively correlated with JA and JA-Ile but not SA. Moreover, soluble sugars positively correlated with IAA and JA but not ABA and SA. We conclude that increasing carbon availability stimulates growth and production of secondary metabolites via up-regulation of auxin and jasmonate levels, probably in response to sugar-mediated signalling. Future low [CO2] studies should address the role of reactive oxygen species (ROS) in leaf ABA and SA biosynthesis, and at the transcriptional level should focus on biosynthetic and, in particular, on responsive genes involved in [CO2]-induced hormonal signalling pathways.

Ethylene and nitric oxide interact to regulate the magnesium deficiency-induced root hair development in Arabidopsis

Nitric oxide (NO) and ethylene respond to biotic and abiotic stresses through either similar or independent processes. This study examines the mechanism underlying the effects of NO and ethylene on promoting root hair development in Arabidopsis under magnesium (Mg) deficiency. The interaction between NO and ethylene in the regulation of Mg deficiency-induced root hair development was investigated using NO- and ethylene-related mutants and pharmacological methods. Mg deficiency triggered a burst of NO and ethylene, accompanied by a stimulated development of root hairs. Interestingly, ethylene facilitated NO generation by activation of both nitrate reductase and nitric oxide synthase-like (NOS-L) in the roots of Mg-deficient plants. In turn, NO enhanced ethylene synthesis through stimulating the activities of 1-aminocyclopropane-1-carboxylate (ACC) oxidase and ACC synthase (ACS). These two processes constituted an NO-ethylene feedback loop. Blocking either of these two processes inhibited the stimulation of root hair development under Mg deficiency. In conclusion, we suggest that Mg deficiency increases the production of NO and ethylene in roots, each influencing the accumulation and role of the other, and thus these two signals interactively regulate Mg deficiency-induced root hair morphogenesis.

An ethylene and ROS-dependent pathway is involved in low ammonium-induced root hair elongation in Arabidopsis seedlings

Root hairs are plastic in response to nutrient supply, but relatively little is known about their development under low ammonium (NH4(+)) conditions. This study showed that reducing NH4(+) for 3 days in wild-type Arabidopsis seedlings resulted in drastic elongation of root hairs. To investigate the possible mediation of ethylene and auxin in this process, seedlings were treated with 2,3,5-triiodobenzoic acid (TIBA, auxin transport inhibitor), 1-naphthylphthalamic acid (NPA, auxin transport inhibitor), p-chlorophenoxy isobutyric acid (PCIB, auxin action inhibitor), aminoethoxyvinylglycine (AVG, chemical inhibitor of ethylene biosynthesis), or silver ions (Ag(+), ethylene perception antagonist) under low NH4(+) conditions. Our results showed that TIBA, NPA and PCIB did not inhibit root hair elongation under low NH4(+) conditions, while AVG and Ag(+) completely inhibited low NH4(+)-induced root hair elongation. This suggested that low NH4(+)-induced root hair elongation was dependent on the ethylene pathway, but not the auxin pathway. Further genetic studies revealed that root hair elongation in auxin-insensitive mutants was sensitive to low NH4(+) treatment, but elongation was less sensitive in ethylene-insensitive mutants than wild-type plants. In addition, low NH4(+)-induced root hair elongation was accompanied by reactive oxygen species (ROS) accumulation. Diphenylene iodonium (DPI, NADPH oxidase inhibitor) and dimethylthiourea (DMTU, ROS scavenger) inhibited low NH4(+)-induced root hair elongation, suggesting that ROS were involved in this process. Moreover, ethylene acted together with ROS to modulate root hair elongation under low NH4(+) conditions. These results demonstrate that a signaling pathway involving ethylene and ROS participates in regulation of root hair elongation when Arabidopsis seedlings are subjected to low NH4(+) conditions.

Physiological and Transcriptome Responses to Combinations of Elevated CO2 and Magnesium in Arabidopsis thaliana

The unprecedented rise in atmospheric CO2 concentration and injudicious fertilization or heterogeneous distribution of Mg in the soil warrant further research to understand the synergistic and holistic mechanisms involved in the plant growth regulation. This study investigated the influence of elevated CO2 (800 μL L(-1)) on physiological and transcriptomic profiles in Arabidopsis cultured in hydroponic media treated with 1 μM (low), 1000 μM (normal) and 10,000 μM (high) Mg2+. Following 7-d treatment, elevated CO2 increased the shoot growth and chlorophyll content under both low and normal Mg supply, whereas root growth was improved exclusively under normal Mg nutrition. Notably, the effect of elevated CO2 on mineral homeostasis in both shoots and roots was less than that of Mg supply. Irrespective of CO2 treatment, high Mg increased number of young leaf but decreased root growth and absorption of P, K, Ca, Fe and Mn whereas low Mg increased the concentration of P, K, Ca and Fe in leaves. Transcriptomics results showed that elevated CO2 decreased the expression of genes related to cell redox homeostasis, cadmium response, and lipid localization, but enhanced signal transduction, protein phosphorylation, NBS-LRR disease resistance proteins and subsequently programmed cell death in low-Mg shoots. By comparison, elevated CO2 enhanced the response of lipid localization (mainly LTP transfer protein/protease inhibitor), endomembrane system, heme binding and cell wall modification in high-Mg roots. Some of these transcriptomic results are substantially in accordance with our physiological and/or biochemical analysis. The present findings broaden our current understanding on the interactive effect of elevated CO2 and Mg levels in the Arabidopsis, which may help to design the novel metabolic engineering strategies to cope with Mg deficiency/excess in crops under elevated CO2.

Elevated CO2-induced production of nitric oxide (NO) by NO synthase differentially affects nitrate reductase activity in Arabidopsis plants under different nitrate supplies

CO2 elevation often alters the plant's nitrate reductase (NR) activity, the first enzyme acting in the nitrate assimilation pathway. However, the mechanism underlying this process remains unknown. The association between elevated CO2-induced alterations of NR activity and nitric oxide (NO) was examined in Col-0 Arabidopsis fed with 0.2-10 mM nitrate, using NO donors, NO scavenger, and NO synthase (NOS) inhibitor. The noa1 mutant, in which most NOS activity was lost, and the NR activity-null mutant nia1 nia2 were also used to examine the above association. In response to CO2 elevation, NR activity increased in low-nitrate Col-0 plants but was inhibited in high-nitrate Col-0 plants. NO scavenger and NOS inhibitor could eliminate these two responses, whereas the application of NO donors mimicked these distinct responses in ambient CO2-grown Col-0 plants. Furthermore, in both low- and high-nitrate conditions, elevated CO2 increased NOS activity and NO levels in Col-0 and nia1 nia2 plants but had little effect on NO level and NR activity in noa1 plants. Considering all of these findings, this study concluded that, in response to CO2 elevation, either the NR activity induction in low-nitrate plants or the NR activity inhibition in high-nitrate plants is regulated by NOS-generated NO.

WUSCHEL-related homeobox gene WOX11 increases rice drought resistance by controlling root hair formation and root system development

Roots are essential organs for anchoring plants, exploring and exploiting soil resources, and establishing plant-microorganisms communities in vascular plants. Rice has a complex root system architecture consisting of several root types, including primary roots, lateral roots, and crown roots. Crown roots constitute the major part of the rice root system and play important roles during the growing period. Recently, we have refined a mechanism that involves ERF3/WOX11 interaction is required to regulate the expression of genes in the cytokinin signaling pathway during the different stages of crown roots development in rice. In this study, we further analyzed the root phenotypes of WOX11 transgenic plants and revealed that WOX11 also acts in controlling root hair development and enhancing rice drought resistance, in addition to its roles in regulating crown root and lateral root development. Based on this new finding, we proposed the mechanism of that WOX11 is involved in drought resistance by modulating rice root system development.

HvEXPB7, a novel β-expansin gene revealed by the root hair transcriptome of Tibetan wild barley, improves root hair growth under drought stress

Tibetan wild barley is a treasure trove of useful genes for crop improvement including abiotic stress tolerance, like drought. Root hair of single-celled structures plays an important role in water and nutrition uptake. Polyethylene-glycol-induced drought stress hydroponic/petri-dish experiments were performed, where root hair morphology and transcriptional characteristics of two contrasting Tibetan wild barley genotypes (drought-tolerant XZ5 and drought-sensitive XZ54) and drought-tolerant cv. Tadmor were compared. Drought-induced root hair growth was only observed in XZ5. Thirty-six drought tolerance-associated genes were identified in XZ5, including 16 genes specifically highly expressed in XZ5 but not Tadmor under drought. The full length cDNA of a novel β-expansin gene (HvEXPB7), being the unique root hair development related gene in the identified genes, was cloned. The sequence comparison indicated that HvEXPB7 carried both DPBB_1 and Pollon_allerg_1 domains. HvEXPB7 is predominantly expressed in roots. Subcellular localization verified that HvEXPB7 is located in the plasma membrane. Barley stripe mosaic virus induced gene silencing (BSMV-VIGS) of HvEXPB7 led to severely suppressed root hairs both under control and drought conditions, and significantly reduced K uptake. These findings highlight and confer the significance of HvEXPB7 in root hair growth under drought stress in XZ5, and provide a novel insight into the genetic basis for drought tolerance in Tibetan wild barley.

Novel imaging-based phenotyping strategies for dissecting crosstalk in plant development

In an era of genomics, proteomics, and metabolomics a large number of mutants are available. The discovery of their phenotypes is fast becoming the bottleneck of molecular plant physiology. This crisis can be overcome by imaging-based phenotyping, an emerging, rapidly developing and innovative approach integrating plant and computer science. A tremendous amount of digital image data are automatically analysed using techniques of 'machine vision'. This minireview will shed light on the available imaging strategies and discuss standard methods for the automated analysis of images to give the non-bioinformatic reader an idea how the new technology works. A number of successful platforms will be described and the prospects that image-based phenomics may offer for elucidating hormonal cross-talk and molecular growth physiology will be discussed.

Phosphorus and magnesium interactively modulate the elongation and directional growth of primary roots in Arabidopsis thaliana (L.) Heynh

A balanced supply of essential nutrients is an important factor influencing root architecture in many plants, yet data related to the interactive effects of two nutrients on root growth are limited. Here, we investigated the interactive effect between phosphorus (P) and magnesium (Mg) on root growth of Arabidopsis grown in pH-buffered agar medium at different P and Mg levels. The results showed that elongation and deviation of primary roots were directly correlated with the amount of P added to the medium but could be modified by the Mg level, which was related to the root meristem activity and stem-cell division. High P enhanced while low P decreased the tip-focused fluorescence signal of auxin biosynthesis, transport, and redistribution during elongation of primary roots; these effects were greater under low Mg than under high Mg. The altered root growth in response to P and Mg supply was correlated with AUX1, PIN2, and PIN3 mRNA abundance and expression and the accumulation of the protein. Application of either auxin influx inhibitor or efflux inhibitor inhibited the elongation and increased the deviation angle of primary roots, and decreased auxin level in root tips. Furthermore, the auxin-transport mutants aux1-22 and eir1-1 displayed reduced root growth and increased the deviation angle. Our data suggest a profound effect of the combined supply of P and Mg on the development of root morphology in Arabidopsis through auxin signals that modulate the elongation and directional growth of primary root and the expression of root differentiation and development genes.

Physiological and molecular alterations in plants exposed to high [CO2] under phosphorus stress

Atmospheric [CO2] has increased substantially in recent decades and will continue to do so, whereas the availability of phosphorus (P) is limited and unlikely to increase in the future. P is a non-renewable resource, and it is essential to every form of life. P is a key plant nutrient controlling the responsiveness of photosynthesis to [CO2]. Increases in [CO2] typically results in increased biomass through stimulation of net photosynthesis, and hence enhance the demand for P uptake. However, most soils contain low concentrations of available P. Therefore, low P is one of the major growth-limiting factors for plants in many agricultural and natural ecosystems. The adaptive responses of plants to [CO2] and P availability encompass alterations at morphological, physiological, biochemical and molecular levels. In general low P reduces growth, whereas high [CO2] enhances it particularly in C3 plants. Photosynthetic capacity is often enhanced under high [CO2] with sufficient P supply through modulation of enzyme activities involved in carbon fixation such as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). However, high [CO2] with low P availability results in enhanced dry matter partitioning towards roots. Alterations in below-ground processes including root morphology, exudation and mycorrhizal association are influenced by [CO2] and P availability. Under high P availability, elevated [CO2] improves the uptake of P from soil. In contrast, under low P availability, high [CO2] mainly improves the efficiency with which plants produce biomass per unit P. At molecular level, the spatio-temporal regulation of genes involved in plant adaptation to low P and high [CO2] has been studied individually in various plant species. Genome-wide expression profiling of high [CO2] grown plants revealed hormonal regulation of biomass accumulation through complex transcriptional networks. Similarly, differential transcriptional regulatory networks are involved in P-limitation responses in plants. Analysis of expression patterns of some typical P-limitation induced genes under high [CO2] suggests that long-term exposure of plants to high [CO2] would have a tendency to stimulate similar transcriptional responses as observed under P-limitation. However, studies on the combined effect of high [CO2] and low P on gene expression are scarce. Such studies would provide insights into the development of P efficient crops in the context of anticipated increases in atmospheric [CO2].

Magnesium availability regulates the development of root hairs in Arabidopsis thaliana (L.) Heynh

Root hairs are reported to be plastic in response to nutrient supply, but relatively little is known about their development in response to magnesium (Mg) availability. Here, we showed that development of root hairs of Arabidopsis decreased progressively with increasing Mg supply, which was related to the initiation of new trichoblast files and likelihood of trichoblasts to form hairs. Tip-focused reactive oxygen species (ROS) and cytosolic Ca(2+) concentrations [(Ca(2+) )c] during elongation of root hairs were enhanced under low Mg but decreased under high Mg. Under low Mg, application of diphenylene iodonium (DPI) or BAPTA [1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid] blocked the enhanced development of root hairs and the opposite was true when the plants under high Mg were treated with phenazine methosulphate (PMS), methyl viologen (MV) or CaCl2 . Furthermore, Mg availability did not alter root hair growth in rhd2-1 mutant that contains lower levels of ROS and cytosolic [Ca(2+) ]c. Transcriptome data and qPCR results revealed a greater fraction of morphogenetic H-genes, and cell wall organization genes were up-regulated by low Mg but down-regulated by high Mg. Our data suggest a profound effect of Mg supply on the development of root hairs in Arabidopsis, through the characterized Ca(2+) and ROS signals that modulate the elongation of root hairs and the expression of root-hair morphogenetic genes.

The effects of carbon dioxide and temperature on microRNA expression in Arabidopsis development

Elevated levels of CO2 and temperature can both affect plant growth and development, but the signalling pathways regulating these processes are still obscure. MicroRNAs function to silence gene expression, and environmental stresses can alter their expressions. Here we identify, using the small RNA-sequencing method, microRNAs that change significantly in expression by either doubling the atmospheric CO2 concentration or by increasing temperature 3-6 °C. Notably, nearly all CO2-influenced microRNAs are affected inversely by elevated temperature. Using the RNA-sequencing method, we determine strongly correlated expression changes between miR156/157 and miR172, and their target transcription factors under elevated CO2 concentration. Similar correlations are also found for microRNAs acting in auxin-signalling, stress responses and potential cell wall carbohydrate synthesis. Our results demonstrate that both CO2 and temperature alter microRNA expression to affect Arabidopsis growth and development, and miR156/157- and miR172-regulated transcriptional network might underlie the onset of early flowering induced by increasing CO2.

The effects of rising atmospheric carbon dioxide on shoot-root nitrogen and water signaling

Terrestrial higher plants are composed of roots and shoots, distinct organs that conduct complementary functions in dissimilar environments. For example, roots are responsible for acquiring water and nutrients such as inorganic nitrogen from the soil, yet shoots consume the majority of these resources. The success of such a relationship depends on excellent root-shoot communications. Increased net photosynthesis and decreased shoot nitrogen and water use at elevated CO2 fundamentally alter these source-sink relations. Lower than predicted productivity gains at elevated CO2 under nitrogen or water stress may indicate shoot-root signaling lacks plasticity to respond to rising atmospheric CO2 concentrations. The following presents recent research results on shoot-root nitrogen and water signaling, emphasizing the influence that rising atmospheric carbon dioxide levels are having on these source-sink interactions.

The phytohormone crosstalk paradigm takes center stage in understanding how plants respond to abiotic stresses

The highly coordinated, dynamic nature of growth requires plants to perceive and react to various environmental signals in an interactive manner. Elaborate signaling networks mediate this plasticity in growth and the ability to adapt to changing environmental conditions. The fluctuations of stress-responsive hormones help alter the cellular dynamics and hence play a central role in coordinately regulating the growth responses under stress. Recent experimental data unequivocally demonstrated that interactions among various phytohormones are the rule rather than exception in integrating the diverse input signals and readjusting growth as well as acquiring stress tolerance. The presence of multiple and often redundant signaling intermediates for each phytohormone appears to help in such crosstalk. Furthermore, there are several examples of similar developmental changes occurring in response to distinct abiotic stress signals, which can be explained by the crosstalk in phytohormone signaling. Therefore, in this brief review, we have highlighted the major phytohormone crosstalks with a focus on the response of plants to abiotic stresses. The recent findings have made it increasingly apparent that such crosstalk will also explain the extreme pleiotropic responses elicited by various phytohormones. Indeed, it would not be presumptuous to expect that in the coming years this paradigm will take a central role in explaining developmental regulation.

Responses of root architecture development to low phosphorus availability: a review

BACKGROUND

Phosphorus (P) is an essential element for plant growth and development but it is often a limiting nutrient in soils. Hence, P acquisition from soil by plant roots is a subject of considerable interest in agriculture, ecology and plant root biology. Root architecture, with its shape and structured development, can be considered as an evolutionary response to scarcity of resources.

SCOPE

This review discusses the significance of root architecture development in response to low P availability and its beneficial effects on alleviation of P stress. It also focuses on recent progress in unravelling cellular, physiological and molecular mechanisms in root developmental adaptation to P starvation. The progress in a more detailed understanding of these mechanisms might be used for developing strategies that build upon the observed explorative behaviour of plant roots.

CONCLUSIONS

The role of root architecture in alleviation of P stress is well documented. However, this paper describes how plants adjust their root architecture to low-P conditions through inhibition of primary root growth, promotion of lateral root growth, enhancement of root hair development and cluster root formation, which all promote P acquisition by plants. The mechanisms for activating alterations in root architecture in response to P deprivation depend on changes in the localized P concentration, and transport of or sensitivity to growth regulators such as sugars, auxins, ethylene, cytokinins, nitric oxide (NO), reactive oxygen species (ROS) and abscisic acid (ABA). In the process, many genes are activated, which in turn trigger changes in molecular, physiological and cellular processes. As a result, root architecture is modified, allowing plants to adapt effectively to the low-P environment. This review provides a framework for understanding how P deficiency alters root architecture, with a focus on integrated physiological and molecular signalling.

Cross-talk between nitric oxide and Ca (2+) in elevated CO 2-induced lateral root formation

This study demonstrates a potential signaling pathway of CO 2-dependent stimulation in lateral root (LR) formation. Elevated CO 2 increases production of nitric oxide (NO), which subsequently stimulates the generation of cytosolic Ca (2+) concentration by activating plasma membrane and/or intracellular Ca (2+)-permeable channels. Meanwhile, nitric oxide synthase (NOS), as one of the main NO source, requires Ca (2+) and CaM as cofactors. This complex interaction involves transduction cascades of multiple signals that lead to the LR formation and development. Finally, this review highlights the the role of Ca (2+) in the process that elevated CO 2 enhances the development of LRs through increased NO level.

Dynamic models of epidermal patterning as an approach to plant eco-evo-devo

Epidermal patterning in Arabidopsis thaliana leaves and root has become a model system for experimental and theoretical developmental studies, yielding well-characterized regulatory networks. We succinctly review the dynamic models proposed for this system and then argue that it provides an excellent instance to integrate and further study the role of non-genetic factors in plant development and evolution. Then, we set up to review the role of phytohormones and environmental stimuli in the regulation of cell-fate determination and patterning in this system. We conclude that dynamic modeling of complex regulatory networks can help understand the plasticity and variability of cellular patterns, and hence, such modeling approaches can be expanded to advance in the consolidation of plant Evolutionary and Ecological Developmental Biology (eco-evo-devo).

Effect of elevated CO₂ on phosphorus nutrition of phosphate-deficient Arabidopsis thaliana (L.) Heynh under different nitrogen forms

Phosphorus (P) nutrition is always a key issue regarding plants responses to elevated CO(2). Yet it is unclear of how elevated CO(2) affects P uptake under different nitrogen (N) forms. This study investigated the influence of elevated CO(2) (800 µl l(-1)) on P uptake and utilization by Arabidopsis grown in pH-buffered phosphate (P)-deficient (0.5 µM) hydroponic culture supplying with 2mM nitrate (NO(3)(-)) or ammonium (NH(4)(+)). After 7 d treatment, elevated CO(2) enhanced the biomass production of both NO(3)(-)- and NH(4) (+)-fed plants but decreased the P amount absorbed per weight of roots and the P concentration in the shoots of plants supplied with NH(4)(+). In comparison, elevated CO(2) increased the amount of P absorbed per weight of roots, as well as the P concentration in plants and alleviated P deficiency-induced symptoms of plants supplied with NO(3)(-). Elevated CO(2) also increased the root/shoot ratio, total root surface area, and acid phosphatase activity, and enhanced the expression of genes or transcriptional factors involving in P uptake, allocation and remobilization in P deficient plants. Furthermore, elevated CO(2) increased the nitric oxide (NO) level in roots of NO(3)(-)-fed plants but decreased it in NH(4)(+)-fed plants. NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) inhibited plant P acquisition by roots under elevated CO(2). Considering all of these findings, this study concluded that a combination of elevated CO(2) and NO(3)(-) nutrition can induce a set of plant adaptive strategies to improve P status from P-deficient soluble sources and that NO may be a signalling molecule that controls these processes.

Nitric oxide enhances development of lateral roots in tomato (Solanum lycopersicum L.) under elevated carbon dioxide

Elevated carbon dioxide (CO₂) has been shown to enhance the growth and development of plants, especially of roots. Amongst them, lateral roots play an important role in nutrient uptake, and thus alleviate the nutrient limitation to plant growth under elevated CO₂. This paper examined the mechanism underlying CO₂ elevation-induced lateral root formation in tomato. The endogenous nitric oxide (NO) in roots was detected by the specific probe 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA). We suggest that CO₂ elevation-induced NO accumulation was important for lateral root formation. Elevated CO₂ significantly increased the activity of nitric oxide synthase in roots, but not nitrate reductase activity. Moreover, the pharmacological evidence showed that nitric oxide synthase rather than nitrate reductase was responsible for CO₂ elevation-induced NO accumulation. Elevated CO₂ enhanced the activity of nitric oxide synthase and promoted production of NO, which was involved in lateral root formation in tomato under elevated CO₂.

Action of gibberellins on growth and metabolism of Arabidopsis plants associated with high concentration of carbon dioxide

Although the positive effect of elevated CO(2) concentration [CO(2)] on plant growth is well known, it remains unclear whether global climate change will positively or negatively affect crop yields. In particular, relatively little is known about the role of hormone pathways in controlling the growth responses to elevated [CO(2)]. Here, we studied the impact of elevated [CO(2)] on plant biomass and metabolism in Arabidopsis (Arabidopsis thaliana) in relation to the availability of gibberellins (GAs). Inhibition of growth by the GA biosynthesis inhibitor paclobutrazol (PAC) at ambient [CO(2)] (350 µmol CO(2) mol(-1)) was reverted by elevated [CO(2)] (750 µmol CO(2) mol(-1)). Thus, we investigated the metabolic adjustment and modulation of gene expression in response to changes in growth of plants imposed by varying the GA regime in ambient and elevated [CO(2)]. In the presence of PAC (low-GA regime), the activities of enzymes involved in photosynthesis and inorganic nitrogen assimilation were markedly increased at elevated [CO(2)], whereas the activities of enzymes of organic acid metabolism were decreased. Under ambient [CO(2)], nitrate, amino acids, and protein accumulated upon PAC treatment; however, this was not the case when plants were grown at elevated [CO(2)]. These results suggest that only under ambient [CO(2)] is GA required for the integration of carbohydrate and nitrogen metabolism underlying optimal biomass determination. Our results have implications concerning the action of the Green Revolution genes in future environmental conditions.

Responses of root hair development to elevated CO2

This review highlights a potential signaling pathway of CO2-dependent stimulation in root hair development. Elevated CO2 firstly increases the carbohydrates production, which triggers the auxin or ethylene responsive signal transduction pathways and subsequently stimulates the generation of intracellular nitric oxide (NO). The NO acts on target Ca2+ and ion channels and induces activation of MAPK. Meanwhile, reactive oxygen species (ROS) activates cytoplasmic Ca2+ channels at the plasma membrane in the apex of the root tip. This complex pathway involves transduction cascades of multiple signals that lead to the fine tuning of epidermal cell initiation and elongation. The results suggest that elevated CO2 plays an important role in cell differentiation processes at the root epidermis.