Coordination of Chloroplastic and Mitochondrial retrograde signaling by RCD1
Signaling from chloroplasts and mitochondria dependent on reactive oxygen species (ROS) and merge at the nuclear protein RCD1, a plant specific hub-protein regulating stress and developmental responses. RCD1 is a multidomain protein where its RST domain mediates interaction with transcription factors and the PARP and WWE-domains bind poly(ADP-ribose), a polymer synthetized by PARPs on nuclear acceptor proteins. RCD1 serves as scaffold for protein complex formation and chloroplastic ROS affect its abundance, redox state and oligomerization. RCD1 interacts with ANAC013 and ANAC017, transcriptional regulators of ROS-related mitochondrial retrograde signaling. Inactivation of RCD1 increases expression of mitochondrial dysfunction stimulon (MDS) genes regulated by ANAC013 and ANAC017, including genes for AOXs. Accumulation of AOXs and other MDS gene products affects respiration and energy metabolism, and alters electron transfer in the chloroplasts, leading to decreased ROS production and increased protection of photosynthetic apparatus. RCD1-dependent regulation is also involved in 3′-phosphoadenosine 5′-phosphate (PAP)-mediated retrograde signaling; a significant overlap exists between genes negatively regulated by RCD1, the MDS genes, and genes affected by PAP. Sensitivity of RCD1 to organellar ROS provides feedback control of nuclear gene expression and RCD1 integrates retrograde signals from both chloroplasts and mitochondria to exert its influence on nuclear gene expression.
Photosynthesis-dependent H2O2 transfer from chloroplasts to nuclei provides a high-light signalling mechanism
Chloroplasts communicate information by retrograde signalling to nuclei during acclimation to increased light intensities. Several potential operating signals originating from chloroplasts have been proposed, but it has proved difficult to establish how such signals are transduced to the nuclei to modulate gene expression. One proposed signal is hydrogen peroxide (H2O2) produced by chloroplasts in a light-dependent manner. We used HyPer2, a genetically-encoded fluorescent H2O2 sensor, to show that in photosynthetic Nicotiana benthamiana epidermal cells, exposure to high light (HL) increased H2O2 production in chloroplast stroma, cytosol and nuclei. Critically, over-expression of stromal ascorbate peroxidase (H2O2 scavenger) or treatment with DCMU (photosynthesis inhibitor) attenuated nuclear H2O2 accumulation and HL-responsive gene expression. In contrast, cytosolic ascorbate peroxidase over-expression had little effect on nuclear H2O2 accumulation and HL-responsive gene expression. This is because the H2O2 is from a sub-population of chloroplasts closely associated with nuclei. Therefore, we have proposed that direct H2O2 transfer from chloroplasts to nuclei, avoiding the cytosol, enables photosynthetic control over gene expression.
Decrypting the plant oxidative stress response
Reactive oxygen species are produced metabolically when excessive energy input exceeds the reducing potential. It is now widely recognized that plants adopted fluctuating perturbations in hydrogen peroxide (H2O2) homeostasis as a first line alerting and signaling system to adjust organellar and cellular metabolism during stress conditions. Unfortunately, our understanding of the signaling network that governs H2O2 sensing, transduction and eventually trigger transcriptional response remains fragmentary. Earlier transcriptomic and genomic-centered studies, provided us first with extra insights in the regulatory networks that govern the oxidative stress response. Recently, tailoring various proteomics technologies allowed us to assess oxidative stress dependent changes at the posttranslational level. Through combined multi-omics efforts, we aim towards a better understanding of how cells interpret the oxidative signals that arise from developmental cues and stress conditions.
How plant cells cope with reactive carbonyl species
During cellular activity, small molecules are constantly exposed to spontaneous reactions and the action of promiscuous enzymes, leading to damage of the molecules. These damaged molecules are in the best case useless but in most cases harmful to the cell. On top of this, abiotic stress conditions stimulate the production of damaged molecules, which further increases the stress for the cell. Small molecule damage can be as critical as DNA, protein or lipid damage in determining cellular fate and plant fitness. Because of this, cells invest a lot of energetic resources to keep damaged molecules under control. Our work focus on reactive oxygen species and reactive carbonyl species. Scavenging mechanisms maintain these reactive species at non-harmful levels, limiting damage and creating cellular messengers.
Reactive carbonyl species are small electrophilic molecules, such as methylglyoxal (MGO). In plants, the main pathway to scavenge MGO is the glyoxalase system, which consists of two enzymes, glyoxylase I and glyoxylase II. These enzymes act in tandem producing D-lactate. We recently discovered and characterized all components of the system, and proposed a cellular model for the detoxification of MGO, which involves the cytosol, chloroplasts, and mitochondria. Moreover, we discovered the pathway of D-lactate metabolization and found modulation of this system by the sugar status of the cell. We now focus on the influences of abiotic stresses on the GLX system.
Reference: Schmitz et al. (2017) Plant Cell 29, 3234-3254.
Waterworld: molecular signalling mechanisms mediating plant flooding tolerance
In an increasingly wetter world, flooding stress is fast emerging as a frequently encountered abiotic stress for plants. Flooding severely restricts plant gas exchange and most terrestrial plants cannot sustain normal functioning under wet conditions. Flooding is a compound stress and associated perturbations in molecules such oxygen, ethylene, reactive oxygen species and carbohydrates can trigger downstream acclimative responses. The changes in these signals can be dynamic and dependent on the plant organ that is flooded and the conditions of flooding. Understanding the role of these signals, their interacting pathways and the changes they trigger to prolong survival in flooded conditions is vital for improving flood tolerance of sensitive plant varieties. In this talk I will highlight our current work on flooding survival mechanisms in the relatively flood intolerant species Arabidopsis thaliana. In particular I will focus on (1) the very early response to flooding (3) and the importance of post flooding recovery.
Root strategies to cope with salt stress: modulating root branching, K+ transport and hormone signalling
Plants can dynamically adapt their root growth in response to various abiotic stresses. Salinity is one of the most devastating abiotic stresses, which modulates both plant Root System Architecture (RSA) and tropism response. Plants’ roots growing away from higher concentrations of NaCl has been described as halotropism. Natural variation via Genome Wide Association Studies (GWAS) as a powerful tool, have identified genetic components important for RSA remodelling and halotropism response. A cytochrome P450 gene, CYP79B2 and HKT1 were validated as being involved in RSA remodelling under salt. Characterization of potassium transporters; CHX13 and NHX5/6, belonging to the CPA (Cation-Proton Antiporters) family proteins, implies the importance of maintaining cytosolic Na+– K+ homeostasis for plant halotropism response. ABA and ethylene are increased upon salt stress and could act as secondary signals activating salt adaptation mechanisms. Our study on mutants of these hormone signalling pathways suggests that ABA and ethylene are required for root halotropism response.
Super Fifty®, a proven tool to prime and protect crops from abiotic stress
Crops are exposed to a number of biotic stresses such as fungus, insects or nematodes during their lifespan. There has been substantial effort and success to mitigate these stresses. The steps taken to mitigate abiotic stress have been largely confined to plant breeding programs. There are few if any tools available to the grower to mitigate drought or heat stress. These two stresses combined caused agricultural losses of $33.3 billion in the US in 2012 (NOAA 2017). In the EU, it is a common phenomenon that temperatures exceed 40oC in southern Europe during the summer season causing seasonal crop failures. BioAtlantis Ltd. in collaboration with research partners in Cropstrengthen have developed a technology to reduce abiotic stress in crops. It involves prior exposure of crops to a particular Ascophyllum nodosum extract called, Super Fifty®. Super Fifty® primed plants will respond faster and stronger when a stress pressure is encountered. The mode-of-action has been identified using ‘OMICS’ tools. The commercial impact of Super Fifty® based stress mitigation technology is quite broad. It has the potential to be used in climate-smart interventions, where weather warnings indicate imminent periods of heat or drought stress. Action taken to apply the product in advance of the stress can result in enhanced stress tolerance to the grower’s crops with monetary benefits. It can also be used to minimise water usage while achieving excellent yields in areas where water is limited or expensive. Further work is necessary to maximise the priming effects and optimise crop recovery. BioAtlantis is quite confident that this will be achieved.
Drought stress protectants in maize
Drought stress is one of the major constraints for maize yield and quality under recent climate changes. Physiological, biochemical and molecular responses of maize plants impair by drought stress condition. It is essential to develop a safe and sustainable means for agriculture production because the overuse of inorganic fertilizers in the agriculture practices lead to environmental pollutions and soil fertility decline. The foliar application of seaweed- and plant-extracts offers eco-alternative ways for protecting plants against stress condition via providing the supply of nutrients and hormone-like compounds causing involvement in antioxidants defence. In this work, we have attempted to explore the best time of application and possible modes of action of antioxidative-protection against drought stress to improve and understand the effects of seaweed- and plant-extracts.
Digital phenotyping; phenotyping the stress effect
Digital Phenotyping is the future for product development in the breeding and crop protection industry. Cameras and sensors can automatically phenotype plants and reveal information about plant morphology, color, root architecture and even physiological traits, while plant development can be followed over time from multiple angles. KeyGene has been using its state of the art in-house high-throughput plant phenotyping systems for more than 10 years now. This has resulted in new insights in yield improvement, mechanisms of growth compounds and difficult-to-measure traits such as stress effects and root development.
At the same time the digital phenotyping field as well as next generation sequencing capabilities have boosted data volumes to enormous sizes and complexities. We have developed next generation data analysis and visualization tools that enable a breeder to absorb such data volumes with ease.
We present a complete solution for data capture, data analysis and data visualization to support digital phenotyping for plant stress effects.
Genetic regulation of barley development under abiotic stress and its impact on yield in a world-wide field study
Since the dawn of agriculture, crop yield has always been impaired through abiotic stresses. In a field trial across five locations worldwide, we tested three abiotic stresses, nitrogen deficiency, drought and salinity, using HEB-YIELD, a selected subset of the wild barley nested association mapping population HEB-25.
We show that barley flowering time genes Ppd-H1, Sdw1, Vrn-H1 and Vrn-H3 exert pleiotropic effects on traits related to plant development and grain yield. Under field conditions, these effects are strongly influenced by environmental cues like day length and temperature. For example, in Al-Karak, Jordan, the day length-sensitive wild barley allele of Ppd-H1 was associated with an increase of grain yield by up to 30% compared to the insensitive elite barley allele. The observed yield increase is accompanied by pleiotropic effects of Ppd-H1 resulting in shorter life cycle, extended grain filling period and increased grain size.
Our study indicates that the adequate timing of plant development is crucial to maximize yield formation under harsh environmental conditions. We provide evidence that wild barley germplasm, introgressed into elite barley cultivars, can be utilized to secure and increase grain yield. The presented knowledge may be transferred to related crop species like wheat and rice to secure the rising global food demand for cereals.
Evening of Tuesday 13th November