Chemical PARP Inhibition Enhances Growth of Arabidopsis and Reduces Anthocyanin Accumulation and the Activation of Stress Protective Mechanisms

Poly-ADP-ribose polymerase (PARP) post-translationally modifies proteins through the addition of ADP-ribose polymers, yet its role in modulating plant development and stress responses is only poorly understood. The experiments presented here address some of the gaps in our understanding of its role in stress tolerance and thereby provide new insights into tolerance mechanisms and growth. Using a combination of chemical and genetic approaches, this study characterized phenotypes associated with PARP inhibition at the physiological level. Molecular analyses including gene expression analysis, measurement of primary metabolites and redox metabolites were used to understand the underlying processes. The analysis revealed that PARP inhibition represses anthocyanin and ascorbate accumulation under stress conditions. The reduction in defense is correlated with enhanced biomass production. Even in unstressed conditions protective genes and molecules are repressed by PARP inhibition. The reduced anthocyanin production was shown to be based on the repression of transcription of key regulatory and biosynthesis genes. PARP is a key factor for understanding growth and stress responses of plants. PARP inhibition allows plants to reduce protection such as anthocyanin, ascorbate or Non-Photochemical-Quenching whilst maintaining high energy levels likely enabling the observed enhancement of biomass production under stress, opening interesting perspectives for increasing crop productivity

Genetic and Molecular Mechanisms Controlling Reactive Oxygen Species and Hormonal Signalling of Cell Death in Response to Environmental Stresses in Arabidopsis thaliana

In the present work the regulation of environmentally induced cell death and signaling of systemic acquired acclimation (SAA) in Arabidopsis thaliana is characterized. We used the lesion simulating disease1 (lsd1) mutant as a model system that is deregulated in light acclimation and programmed cell death (PCD). In this system we identify that redox status controlling SAA and cell death is controlled by the genes LSD1, EDS1, EIN2 and PAD4 which regulate cellular homeostasis of salicylic acid (SA), ethylene (ET), auxin (IAA) and reactive oxygen species (ROS). Furthermore we propose that the roles of LSD1 in light acclimation and in biotic stress are functionally linked. The influence of SA on plant growth, short-term acclimation to high light (HL), and on the redox homeostasis of Arabidopsis leaves was also assessed. SA impaired acclimation of wild-type plants to prolonged conditions of excess excitation energy (EEE). This indicates an essential role of SA in acclimation and regulation of cellular redox homeostasis. We also show that cell death in response to EEE is controlled by specific redox changes of photosynthetic electron transport carriers that normally regulate EEE acclimation. These redox changes cause production of ET that signals through the EIN2 gene and regulon. In the lsd1 mutant, we found that propagation of cell death depends on the plant defence regulators EDS1 and PAD4 operating upstream of ET production. We conclude that the balanced activities of LSD1, EDS1, PAD4 and EIN2 regulate chloroplast dependent acclimatory and defence responses. Furthermore, we show that Arabidopsis hypocotyls form lysigenous aerenchyma in response to hypoxia and that this process involves H2O2 and ET signalling. We found that formation of lysigenous aerenchyma depends on LSD1, EDS1 and PAD4. Conclusively we show that LSD1, EDS1 and PAD4, in their functions as major plant redox and hormone regulators provide a basis for fundamental plant survival in natural contitions

Lysigenous Aerenchyma Formation in Arabidopsis Is Controlled by LESION SIMULATING DISEASE1[W][OA]

Aerenchyma tissues form gas-conducting tubes that provide roots with oxygen under hypoxic conditions. Although aerenchyma have received considerable attention in Zea mays, the signaling events and genes controlling aerenchyma induction remain elusive. Here, we show that Arabidopsis thaliana hypocotyls form lysigenous aerenchyma in response to hypoxia and that this process involves H2O2 and ethylene signaling. By studying Arabidopsis mutants that are deregulated for excess light acclimation, cell death, and defense responses, we find that the formation of lysigenous aerenchyma depends on the plant defense regulators LESION SIMULATING DISEASE1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), and PHYTOALEXIN DEFICIENT4 (PAD4) that operate upstream of ethylene and reactive oxygen species production. The obtained results indicate that programmed cell death of lysigenous aerenchyma in hypocotyls occurs in a similar but independent manner from the foliar programmed cell death. Thus, the induction of aerenchyma is subject to a genetic and tissue-specific program. The data lead us to conclude that the balanced activities of LSD1, EDS1, and PAD4 regulate lysigenous aerenchyma formation in response to hypoxia

Spreading the news: subcellular and organellar reactive oxygen species production and signalling

This review aims to depict the current knowledge on signalling events that are mediated by reactive oxygen species originating in the organelles.As plants are sessile organisms that have to attune their physiology and morphology continuously to varying environmental challenges in order to survive and reproduce, they have evolved complex and integrated environment-cell, cell-cell, and cell-organelle signalling circuits that regulate and trigger the required adjustments (such as alteration of gene expression). Although reactive oxygen species (ROS) are essential components of this network, their pathways are not yet completely unravelled. In addition to the intrinsic chemical properties that define the array of interaction partners, mobility, and stability, ROS signalling specificity is obtained via the spatiotemporal control of production and scavenging at different organellar and subcellular locations (e.g. chloroplasts, mitochondria, peroxisomes, and apoplast). Furthermore, these cellular compartments may crosstalk to relay and further fine-tune the ROS message. Hence, plant cells might locally and systemically react upon environmental or developmental challenges by generating spatiotemporally controlled dosages of certain ROS types, each with specific chemical properties and interaction targets, that are influenced by interorganellar communication and by the subcellular location and distribution of the involved organelles, to trigger the suitable acclimation responses in association with other well-established cellular signalling components (e.g. reactive nitrogen species, phytohormones, and calcium ions). Further characterization of this comprehensive ROS signalling matrix may result in the identification of new targets and key regulators of ROS signalling, which might be excellent candidates for engineering or breeding stress-tolerant plants

Effector-driven marker development and cloning of resistance genes against Phytophthora infestans in potato breeding clone SW93-1015

Key message: We show the usefulness of integrating effector screening in a breeding program and in resistance gene cloning, withPhytophthoraresistance in the Swedish potato breeding clone SW93-1015 as an example. Abstract: Phytophthora infestans is one of the most devastating plant pathogens worldwide. We have earlier found that the SW93-1015 potato breeding clone has an efficient resistance against P. infestans under field conditions in Sweden, which has an unusually high local diversity of the pathogen. This potato clone has characteristics that are different from classical R-gene-mediated resistance such as elevated levels of hydrogen peroxide (H2O2) under controlled conditions. Analysis of 76 F1 potato progenies from two individual crosses resulted in nearly 50 % resistant clones, from both crosses. This result suggests that the SW93-1015 clone has a simplex genotype for this trait. Screening with over 50 different P. infestans effectors, containing the conserved motif RXLR (for Arg, any amino acid, Leu, Arg), revealed a specific response to Avr2, which suggests that SW93-1015 might contain a functional homolog of the R2 resistance gene. We cloned eight R2 gene homologs from SW93-1015, whereof seven have not been described before and one gene encoded a protein identical to Rpi-ABPT. Expression of this gene in potato cultivar Désirée provided R2-specific resistance, whereas other homologues did not. Using RNAseq analyses we designed a new DNA marker for the R2 resistance in SW93-1015. In summary, we have demonstrated the use of effector screening in practical breeding material and revealed the key resistance mechanism for SW93-1015

Mitochondrial perturbation negatively affects auxin signaling

Mitochondria are crucial players in the signaling and metabolic homeostasis of the plant cell. The molecular components that orchestrate the underlying processes, however, are largely unknown. Using a chemical biology approach, we exploited the responsiveness of Arabidopsis UDP-glucosyltransferase-encoding UGT74E2 towards mitochondrial perturbation in order to look for novel mechanisms regulating mitochondria-to-nucleus communication. The most potent inducers of UGT74E2 shared a (2-furyl) acrylate (FAA) substructure that negatively affected mitochondrial function and was identified before as an auxin transcriptional inhibitor. Based on these premises, we demonstrated that perturbed mitochondria negatively affect the auxin signaling machinery. Moreover, chemical perturbation of polar auxin transport and auxin biosynthesis was sufficient to induce mitochondrial retrograde markers and their transcript abundance was constitutively elevated in the absence of the auxin transcriptional activators ARF7 and ARF19

Activation of auxin signalling counteracts photorespiratory H2O2-dependent cell death

The high metabolic flux through photorespiration constitutes a significant part of the carbon cycle. Although the major enzymatic steps of the photorespiratory pathway are well characterized, little information is available on the functional significance of photorespiration beyond carbon recycling. Particularly important in this respect is the peroxisomal catalase activity which removes photorespiratory H2O2 generated during the oxidation of glycolate to glyoxylate, thus maintaining the cellular redox homeostasis governing the perception, integration and execution of stress responses. By performing a chemical screen, we identified 34 small molecules that alleviate the negative effects of photorespiration in Arabidopsis thaliana mutants lacking photorespiratory catalase (cat2). The chlorophyll fluorescence parameter photosystem II maximum efficiency (F-v/F-m) was used as a high-throughput readout. The most potent chemical that could rescue the photorespiratory phenotype of cat2 is a pro-auxin that contains a synthetic auxin-like substructure belonging to the phenoxy herbicide family, which can be released in planta. The naturally occurring indole-3-acetic acid (IAA) and other chemically distinct synthetic auxins also inhibited the photorespiratory-dependent cell death in cat2 mutants, implying a role for auxin signalling in stress tolerance. Although the photorespiratory pathway is biochemically well characterized, little information is available on the functional significance of photorespiration beyond carbon recycling. Particularly important in this respect is theperoxisomal catalase activity which removes photorespiratory H2O2.. By perfroming a chemical screen, we identified 34 small molecules that alleviate the negative effects of photorespiration in Arabidopsis thaliana mutants lacking photorespiratory catalase (cat2). The most potent chemical that could rescue the photorespiratory phenotype of cat2 is a pro-auxin structure, implying a role for auxin signaling in stress tolerance