Publikationen - Molekulare Signalverarbeitung

Background  In viticulture, iron (Fe) chlorosis is a common abiotic stress that impairs plant development and leads to yield and quality losses. Under low availability of the metal, the applied N form (nitrate and ammonium) can play a role in promoting or mitigating Fe deficiency stresses. However, the processes involved are not clear in grapevine. Therefore, the aim of this study was to investigate the response of two grapevine rootstocks to the interaction between N forms and Fe uptake. This process was evaluated in a hydroponic experiment using two ungrafted grapevine rootstocks Fercal (Vitis berlandieri x V. vinifera) tolerant to deficiency induced Fe chlorosis and Couderc 3309 (V. riparia x V. rupestris) susceptible to deficiency induced Fe chlorosis. Results  The results could differentiate Fe deficiency effects, N-forms effects, and rootstock effects. Interveinal chlorosis of young leaves appeared earlier on 3309 C from the second week of treatment with NO3−/NH4+ (1:0)/-Fe, while Fercal leaves showed less severe symptoms after four weeks of treatment, corresponding to decreased chlorophyll concentrations lowered by 75% in 3309 C and 57% in Fercal. Ferric chelate reductase (FCR) activity was by trend enhanced under Fe deficiency in Fercal with both N combinations, whereas 3309 C showed an increase in FCR activity under Fe deficiency only with NO3−/NH4+ (1:1) treatment. With the transcriptome analysis, Gene Ontology (GO) revealed multiple biological processes and molecular functions that were significantly regulated in grapevine rootstocks under Fe-deficient conditions, with more genes regulated in Fercal responses, especially when both forms of N were supplied. Furthermore, the expression of genes involved in the auxin and abscisic acid metabolic pathways was markedly increased by the equal supply of both forms of N under Fe deficiency conditions. In addition, changes in the expression of genes related to Fe uptake, regulation, and transport reflected the different responses of the two grapevine rootstocks to different N forms. Conclusions  Results show a clear contribution of N forms to the response of the two grapevine rootstocks under Fe deficiency, highlighting the importance of providing both N forms (nitrate and ammonium) in an appropriate ratio in order to ease the rootstock responses to Fe deficiency.

The shape of tomato fruits is closely correlated to microtubule organization and the activity of microtubule associated proteins (MAP), but insights into the mechanism from a cell biology perspective are still largely elusive. Analysis of tissue expression profiles of different microtubule regulators revealed that functionally distinct classes of MAPs are highly expressed during fruit development. Among these, several members of the plant-specific MAP70 family are preferably expressed at the initiation stage of fruit development. Transgenic tomato lines overexpressing SlMAP70 produced elongated fruits that show reduced cell circularity and microtubule anisotropy, while SlMAP70 loss-of-function mutant showed an opposite effect with flatter fruits. Microtubule anisotropy of fruit endodermis cells exhibited dramatic rearrangement during tomato fruit development, and SlMAP70-1 is likely implicated in cortical microtubule organization and fruit elongation throughout this stage by interacting with SUN10/SlIQD21a. The expression of SlMAP70 (or co-expression of SlMAP70 and SUN10/SlIQD21a) induces microtubule stabilization and prevents its dynamic rearrangement, both activities are essential for fruit shape establishment after anthesis. Together, our results identify SlMAP70 as a novel regulator of fruit elongation, and demonstrate that manipulating microtubule stability and organization at the early fruit developmental stage has a strong impact on fruit shape.

The structure of the microtubule cytoskeleton provides valuable information related to morphogenesis of cells. The cytoskeleton organizes into diverse patterns that vary in cells of different types and tissues, but also within a single tissue. To assess differences in cytoskeleton organization methods are needed that quantify cytoskeleton patterns within a complete cell and which are suitable for large data sets. A major bottleneck in most approaches, however, is a lack of techniques for automatic extraction of cell contours. Here, we present a semi-automatic pipeline for cell segmentation and quantification of microtubule organization. Automatic methods are applied to extract major parts of the contours and a handy image editor is provided to manually add missing information efficiently. Experimental results prove that our approach yields high-quality contour data with minimal user intervention and serves a suitable basis for subsequent quantitative studies.

Jasmonic acid and other fatty‐acid‐derived compounds called oxylipins are signals in stress responses and development of plants. The receptor complex, signal transduction components as well as repressors and activators in jasmonate‐induced gene expression have been elucidated. Different regulatory levels and cross‐talk with other hormones are responsible for the multiplicity of plant responses to environmental and developmental cues.

Mutualistic symbioses between plant roots and microorganisms can reduce the demand for chemical fertilizers in agriculture. Most crops are able to establish arbuscular mycorrhiza (AM) symbiosis with fungi to take up phosphate more efficiently. A second symbiosis, nitrogen-fixing root nodule symbiosis, supersedes energy-intensive nitrogen fertilization: Legumes such as peas, clover and soybeans take up rhizobia – special bacteria that are capable of converting atmospheric nitrogen into ammonium – into their root cells. Plant root cells perceive rhizobia and AM fungi via very similar signaling molecules (N-acetylglucosamine tetra- or pentamers), even though the resultant developmental processes differ strongly. Interestingly, N-acetylglucosamine containing signals including fungal chitin- and bacterial peptidoglycan-fragments from their cell walls, also play a role in the recognition of pathogenic microorganisms.Despite the intrinsic sustainability potential of the nitrogen-fixing root nodule symbiosis, too much of a good thing, however, has led to global problems: The massive increase in global meat production is largely based on soybean. Large scale soybean monoculture destroyed ecosystems in South America. Large scale animal production results in excessive methane and nitrogen release into the environment, which causes climate change and death zones in marine ecosystems, respectively. This calls for a considerable reduction in meat consumption.

BackgroundPerception and transduction of temperature changes result in altered growth enabling plants to adapt to increased ambient temperature. While PHYTOCHROME-INTERACTING FACTOR4 (PIF4) has been identified as a major ambient temperature signaling hub, its upstream regulation seems complex and is poorly understood. Here, we exploited natural variation for thermo-responsive growth in Arabidopsis thaliana using quantitative trait locus (QTL) analysis.ResultsWe identified GIRAFFE2.1, a major QTL explaining ~18 % of the phenotypic variation for temperature-induced hypocotyl elongation in the Bay-0 x Sha recombinant inbred line population. Transgenic complementation demonstrated that allelic variation in the circadian clock regulator EARLY FLOWERING3 (ELF3) is underlying this QTL. The source of variation could be allocated to a single nucleotide polymorphism in the ELF3 coding region, resulting in differential expression of PIF4 and its target genes, likely causing the observed natural variation in thermo-responsive growth.ConclusionsIn combination with other recent studies, this work establishes the role of ELF3 in the ambient temperature signaling network. Natural variation of ELF3-mediated gating of PIF4 expression during nightly growing periods seems to be affected by a coding sequence quantitative trait nucleotide that confers a selective advantage in certain environments. In addition, natural ELF3 alleles seem to differentially integrate temperature and photoperiod information to induce architectural changes. Thus, ELF3 emerges as an essential coordinator of growth and development in response to diverse environmental cues and implicates ELF3 as an important target of adaptation.

Plant secondary metabolites, also termed specialized plant metabolites, currently comprise more than 200 000 natural products that are all based on a few biosynthetic pathways and key primary metabolites. Some pathways like flavonoid and terpenoid biosynthesis are universally distributed in the plant kingdom, whereas others like alkaloid or cyanogenic glycoside biosynthesis are restricted to a limited set of taxa. Diversification is achieved by an array of mechanisms at the genetic and enzymatic level including gene duplications, substrate promiscuity of enzymes, cell‐specific regulatory systems, together with modularity and combinatorial aspects. Specialized metabolites reflect adaptations to a specific environment. The observed diversity illustrates the heterogeneity and multitude of ecological habitats and niches that plants have colonized so far and constitutes a reservoir of potential new metabolites that may provide adaptive advantage in the face of environmental changes. The code that connects the observed chemical diversity to this ecological diversity is largely unknown. One way to apprehend this diversity is to realize its tremendous plasticity and evolutionary potential. This chapter presents an overview of the most widespread and popular secondary metabolites, which provide a definite advantage to adapt to or to colonize a particular environment, making the boundary between the “primary” and the “secondary” old fashioned and blurry.

Jasmonates are lipid-derived compounds which are signals in plant stress responses and development. They are synthesized in chloroplasts and peroxisomes. An endogenous rise occurs upon environmental stimuli or in distinct stages of development such as that of anthers and trichomes or in root growth. Hydroxylation, carboxylation, glucosylation, sulfation, methylation, or conjugation of jasmonic acid (JA) leads to numerous metabolites. Many of them are at least partially biologically inactive. The most bioactive JA is the (+)-7-iso-JA–isoleucine conjugate. Its perception takes place by the SCFCOI1-JAZ-co-receptor complex. At elevated levels of JAs, negative regulators such as JAZ, or JAV are subjected to proteasomal degradation, thereby allowing positively acting transcription factors of the MYC or MYB family to switch on JA-induced gene expression. In case of JAM negative regulation takes place by anatagonism to MYC2. JA and COI1 are dominant signals in gene expression after wounding or in response to necrotrophic pathogens. Cross-talk to salicylic acid, ethylene, auxin, and other hormones occurs. Growth is inhibited by JA, thereby counteracting the growth stimulation by gibberellic acid. Senescence, trichome formation, arbuscular mycorrhiza, and formation of many secondary metabolites are induced by jasmonates. Effects in cold acclimation; in intercropping; during response to herbivores, nematodes, or necrotrophic pathogens; in pre- and post-harvest; in crop quality control; and in biosynthesis of secondary compounds led to biotechnological and agricultural applications.

The definition of a plant hormone has not been clearly established, so the compounds classified as plant hormones often vary depending on which definition is considered. In this chapter, auxins, gibberellins (GAs), cytokinins, abscisic acid, brassinosteroids, jasmonic acid-related compounds, and ethylene are described as established plant hormones, while polyamines and phenolic compounds are not included. On the other hand, several peptides that have been proven to play a clear physiological role(s) in plant growth and development, similar to the established plant hormones, are referred. This chapter will focus primarily on the more recent discoveries of plant hormones and their impact on our current understanding of their biological role. In some cases, however, it is critical to place recent work in a proper historical context.

This chapter contains sections titled:IntroductionJA BiosynthesisJA MetabolismBound OPDA – ArabidopsidesMutants of JA Biosynthesis and SignalingCOI1–JAZ–JA‐Ile‐Mediated JA SignalingTranscription Factors Involved in JA SignalingJasmonates and Oxylipins in DevelopmentConclusionsAcknowledgmentsReferences