Plants are necessarily highly competitive and have finely tuned mechanisms to adjust growth and development in accordance with opportunities and limitations in their environment. Sugars from ...photosynthesis form an integral part of this growth control process, acting as both an energy source and as signaling molecules in areas targeted for growth. The plant hormone auxin similarly functions as a signaling molecule and a driver of growth and developmental processes. Here, we show that not only do the two act in concert but that auxin metabolism is itself regulated by the availability of free sugars. The regulation of the biosynthesis and degradation of the main auxin, indole-3-acetic acid (IAA), by sugars requires changes in the expression of multiple genes and metabolites linked to several IAA biosynthetic pathways. The induction also involves members of the recently described central regulator PHYTOCHROME-INTERACTING FACTOR transcription factor family. Linking these three known regulators of growth provides a model for the dynamic coordination of responses to a changing environment.
Together, auxin and cytokinin regulate many of the processes that are critical to plant growth, development, and environmental responsiveness. We have previously shown that exogenous auxin regulates ...cytokinin biosynthesis in Arabidopsis thaliana. In this work, we show that, conversely, the application or induced ectopic biosynthesis of cytokinin leads to a rapid increase in auxin biosynthesis in young, developing root and shoot tissues. We also show that reducing endogenous cytokinin levels, either through the induction of CYTOKININ OXIDASE expression or the mutation of one or more of the cytokinin biosynthetic ISOPENTENYLTRANSFERASE genes leads to a reduction in auxin biosynthesis. Cytokinin modifies the abundance of transcripts for several putative auxin biosynthetic genes, suggesting a direct induction of auxin biosynthesis by cytokinin. Our data indicate that cytokinin is essential, not only to maintain basal levels of auxin biosynthesis in developing root and shoot tissues but also for the dynamic regulation of auxin biosynthesis in response to changing developmental or environmental conditions. In combination with our previous work, the data suggest that a homeostatic feedback regulatory loop involving both auxin and cytokinin signaling acts to maintain appropriate auxin and cytokinin concentrations in developing root and shoot tissues.
Summary
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Populus has become an important model plant system. However, utilization of the increasingly extensive collection of genetics and genomics data created by the community is currently ...hindered by the lack of a central resource, such as a model organism database (MOD). Such MODs offer a single entry point to the collection of resources available within a model system, typically including tools for exploring and querying those resources.
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As a starting point to overcoming the lack of such an MOD for Populus, we present the Populus Genome Integrative Explorer (PopGenIE), an integrated set of tools for exploring the Populus genome and transcriptome. The resource includes genome, synteny and quantitative trait locus (QTL) browsers for exploring genetic data.
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Expression tools include an electronic fluorescent pictograph (eFP) browser, expression profile plots, co‐regulation within collated transcriptomics data sets, and identification of over‐represented functional categories and genomic hotspot locations. A number of collated transcriptomics data sets are made available in the eFP browser to facilitate functional exploration of gene function. Additional homology and data extraction tools are provided.
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PopGenIE significantly increases accessibility to Populus genomics resources and allows exploration of transcriptomics data without the need to learn or understand complex statistical analysis methods. PopGenIE is available at http://www.popgenie.org or via http://www.populusgenome.info.
Plants grown at high densities perceive a decrease in the red to far-red (R:FR) ratio of incoming light, resulting from absorption of red light by canopy leaves and reflection of far-red light from ...neighboring plants. These changes in light quality trigger a series of responses known collectively as the shade avoidance syndrome. During shade avoidance, stems elongate at the expense of leaf and storage organ expansion, branching is inhibited, and flowering is accelerated. We identified several loci in Arabidopsis, mutations in which lead to plants defective in multiple shade avoidance responses. Here we describe TAA1, an aminotransferase, and show that TAA1 catalyzes the formation of indole-3-pyruvic acid (IPA) from L-tryptophan (L-Trp), the first step in a previously proposed, but uncharacterized, auxin biosynthetic pathway. This pathway is rapidly deployed to synthesize auxin at the high levels required to initiate the multiple changes in body plan associated with shade avoidance.
The rate and plane of cell division and anisotropic cell growth are critical for plant development and are regulated by diverse mechanisms involving several hormone signaling pathways. Little is ...known about peptide signaling in plant growth; however, Arabidopsis thaliana POLARIS (PLS), encoding a 36-amino acid peptide, is required for correct root growth and vascular development. Mutational analysis implicates a role for the peptide in hormone responses, but the basis of PLS action is obscure. Using the Arabidopsis root as a model to study PLS action in plant development, we discovered a link between PLS, ethylene signaling, auxin homeostasis, and microtubule cytoskeleton dynamics. Mutation of PLS results in an enhanced ethylene-response phenotype, defective auxin transport and homeostasis, and altered microtubule sensitivity to inhibitors. These defects, along with the short-root phenotype, are suppressed by genetic and pharmacological inhibition of ethylene action. PLS expression is repressed by ethylene and induced by auxin. Our results suggest a mechanism whereby PLS negatively regulates ethylene responses to modulate cell division and expansion via downstream effects on microtubule cytoskeleton dynamics and auxin signaling, thereby influencing root growth and lateral root development. This mechanism involves a regulatory loop of auxin-ethylene interactions.
Summary
Gynoecia of the Arabidopsis mutant sty1‐1 display abnormal style morphology and altered vascular patterning. These phenotypes, which are enhanced in the sty1‐1 sty2‐1 double mutant, suggest ...that auxin homeostasis or signalling might be affected by mutations in STY1 and STY2, both members of the SHI gene family. Chemical inhibition of polar auxin transport (PAT) severely affects the apical–basal patterning of the gynoecium, as do mutations in the auxin transport/signalling genes PIN1, PID and ETT. Here we show that the apical–basal patterning of sty1‐1 and sty1‐1 sty2‐1 gynoecia is hypersensitive to reductions in PAT, and that sty1‐1 enhances the PAT inhibition‐like phenotypes of pin1‐5, pid‐8 and ett‐1 gynoecia. Furthermore, we show that STY1 activates transcription of the flavin monooxygenase‐encoding gene THREAD/YUCCA4, involved in auxin biosynthesis, and that changes in expression of STY1 and related genes lead to altered auxin homeostasis. Our results suggest that STY1 and related genes promote normal development of the style and affect apical–basal patterning of the gynoecium through regulation of auxin homeostasis.
One of the most long-lived models in plant science is the belief that the long-distance transport and ratio of two plant hormones, auxin and cytokinin, at the site of action control major ...developmental events such as apical dominance. We have used in vivo deuterium labeling and mass spectrometry to investigate the dynamics of homeostatic cross talk between the two plant hormones. Interestingly, auxin mediates a very rapid negative control of the cytokinin pool by mainly suppressing the biosynthesis via the isopentenyladenosine-5′-monophosphate-independent pathway. In contrast, the effect of cytokinin overproduction on the entire auxin pool in the plant was slower, indicating that this most likely is mediated through altered development. In addition, we were able to confirm that the lateral root meristems are likely to be the main sites of isopentenyladenosine-5′-monophosphate-dependent cytokinin synthesis, and that the aerial tissue of the plant surprisingly also was a significant source of cytokinin biosynthesis. Our demonstration of shoot-localized synthesis, together with data demonstrating that auxin imposes a very rapid regulation of cytokinin biosynthesis, illustrates that the two hormones can interact also on the metabolic level in controlling plant development, and that the aerial part of the plant has the capacity to synthesize its own cytokinin independent of long-range transport from the root system.
Summary
The distribution and biosynthesis of indole‐3‐acetic acid (IAA) was investigated during early plant development in Arabidopsis. The youngest leaves analysed, less than 0.5 mm in length, ...contained 250 pg mg−1 of IAA and also exhibited the highest relative capacity to synthesize this hormone. A decrease of nearly one hundred‐fold in IAA content occurred as the young leaves expanded to their full size, and this was accompanied by a clear shift in both pool size and IAA synthesis capacity. The correlation between high IAA content and intense cell division was further verified in tobacco leaves, where a detailed analysis revealed that dividing mesophyll tissue contained ten‐fold higher IAA levels than tissue growing solely by elongation. We demonstrated that all parts of the young Arabidopsis plant can potentially contribute to the auxin needed for growth and development, as not only young leaves, but also all other parts of the plant such as cotyledons, expanding leaves and root tissues have the capacity to synthesize IAA de novo. We also observed that naphthylphthalamic acid (NPA) treatment induced tissue‐dependent feedback inhibition of IAA biosynthesis in expanding leaves and cotyledons, but intriguingly not in young leaves or in the root system. This observation supports the hypothesis that there is a sophisticated tissue‐specific regulatory mechanism for auxin biosynthesis. Finally, a strict requirement for maintaining the pool sizes of IAA was revealed as reductions in leaf expansion followed both decreases and increases in the IAA levels in developing leaves. This indicates that leaves are not only important sources for IAA synthesis, but that normal leaf expansion depends on rigorous control of IAA homeostasis.
A Latin hypercube sampling method, including a reduction of spurious correlation in input data, is suggested for stochastic finite element analysis. This sampling procedure strongly improves the ...representation of stochastic design parameters compared to a standard Monte Carlo sampling. As the correlation control requires the number of realizations to be larger than the number of stochastic variables in the problem, a principal component analysis is employed to reduce the number of stochastic variables. In many cases, this considerably relaxes the restriction on the number of realizations. The method presented offers the same general applicability as the standard Monte Carlo sampling method but is superior in computational efficiency.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Summary
Lateral root formation is profoundly affected by auxins. Here we present data which indicate that light influences the formation of indole‐3‐acetic acid (IAA) in germinating Arabidopsis ...seedlings. IAA transported from the developing leaves to the root system is detectable as a short‐lived pulse in the roots and is required for the emergence of the lateral root primordia (LRP) during early seedling development. LRP emergence is inhibited by the removal of apical tissues prior to detection of the IAA pulse in the root, but this treatment has minimal effects on LRP initiation. Our results identify the first developing true leaves as the most likely source for the IAA required for the first emergence of the LRP, as removal of cotyledons has only a minor effect on LRP emergence in contrast to removal of the leaves. A basipetal IAA concentration gradient with high levels of IAA in the root tip appears to control LRP initiation, in contrast to their emergence. A significant increase in the ability of the root system to synthesize IAA is observed 10 days after germination, and this in turn is reflected in the reduced dependence of the lateral root emergence on aerial tissue‐derived auxin at this stage. We propose a model for lateral root formation during early seedling development that can be divided into two phases: (i) an LRP initiation phase dependent on a root tip‐localized IAA source, and (ii) an LRP emergence phase dependent on leaf‐derived IAA up to 10 days after germination.
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