Reactive oxygen species in plant development

Reactive oxygen species (ROS) are produced by metabolic pathways in almost all cells. As signaling components, ROS are best known for their roles in abiotic and biotic stress-related events. However, recent studies have revealed that they are also involved in numerous processes throughout the plant life cycle, from seed development and germination, through to root, shoot and flower development. Here, we provide an overview of ROS production and signaling in the context of plant growth and development, highlighting the key functions of ROS and their interactions with plant phytohormonal networks

Fatal attraction: the intuitive appeal of GMO opposition

Public opposition to genetically modified organisms (GMOs) remains strong. By contrast, studies demonstrate again and again that GM crops make a valuable contribution to the development of a sustainable type of agriculture. The discrepancy between public opinion and the scientific evidence requires an explanation. We argue that intuitive expectations about the world render the human mind vulnerable to particular misrepresentations of GMOs. We explain how the involvement of particular intuitions accounts for the popularity, persistence, and typical features of GM opposition and tackle possible objections to our approach. To conclude, we discuss the implications for science education, science communication, and the environmental movement

A chemoselective and continuous synthesis of m-sulfamoylbenzamide analogues

For the synthesis of m-sulfamoylbenzamide analogues, small molecules which are known for their bioactivity, a chemoselective procedure has been developed starting from m-(chlorosulfonyl) benzoyl chloride. Although a chemoselective process in batch was already reported, a continuous-flow process reveals an increased selectivity at higher temperatures and without catalysts. In total, 15 analogues were synthesized, using similar conditions, with yields ranging between 65 and 99%. This is the first automated and chemoselective synthesis of m- sulfamoylbenzamide analogues

Plant proteases

Plant proteases are involved in most aspects of plant physiology and development, playing key roles in the generation of signaling molecules and as regulators of essential cellular processes such as cell division and metabolism. They take part in important pathways like protein turnover by the degradation of misfolded proteins and the ubiquitin-proteasome pathway, and they are responsible for post-translational modifications of proteins by proteolysis at highly specific sites. Proteases are also implicated in a great variety of environmentally controlled processes, including mobilization of storage proteins during seed germination, development of seedlings, senescence, programmed cell death and defense mechanisms against pests and pathogens. However, in spite of their importance, little is known about the functions and mode of actions of specific plant proteases. This Research Topic aims to collect contributions covering diverse aspects of plant proteases research, including: • Plant proteases biological role and functional characterization • Process regulation by plant proteases and their inhibitors • Development of strategies to monitor and alter plant proteases activity • Elucidation of the biochemistry of specific protease families • Novel technologies to study proteases and identify their natural substrates • New methods that can be used to track and inhibit protease activity at the molecular level and their biotechnological applications • Recent advances in the use of structural biology to study individual proteases and proteases that are part of larger complexes We encourage all scientists engaged in plant proteases research to participate this Research Topic. Original research articles and reviews are welcome

Secondary sulfur metabolism in cellular signalling and oxidative stress responses

The sulfur metabolism pathway in plants produces a variety of compounds that are central to the acclimation response to oxidative stresses such as drought and high light. Primary sulfur assimilation provides the amino acid cysteine, which is utilized in protein synthesis and as a precursor for the cellular redox buffer glutathione. In contrast, the secondary sulfur metabolism pathway produces sulfated compounds such as glucosinolates and sulfated peptides, as well as a corresponding by-product 3'-phosphoadenosine 5'-phosphate (PAP). Emerging evidence over the past decade has shown that secondary sulfur metabolism also has a crucial engagement during oxidative stress. This occurs across various cellular, tissue and organismal levels including chloroplast-to-nucleus retrograde signalling events mediated by PAP, modulation of hormonal signalling by sulfated compounds and PAP, control of physiological responses such as stomatal closure, and potential regulation of plant growth. In this review, we examine the contribution of the different components of plant secondary metabolism to oxidative stress homeostasis, and how this pathway is metabolically regulated. We further outline the key outstanding questions in the field that are necessary to understand how and why this 'specialized' metabolic pathway plays significant roles in plant oxidative stress tolerance

Plant proteases and programmed cell death

Proteolysis affects many processes in plant development and during stress responses, as well as being crucial in cellular protein homeostasis and recycling of resources. Beyond bulk degradation, proteases can have important signaling functions or affect cellular pathways by precise cleavage of signaling proteins. This special issue covers key research themes in the diverse but increasingly interconnected fields of programmed cell death (PCD) and plant protease activity. Future trends are also highlighted, such as accelerated substrate discovery facilitated by large-scale deposition of N-terminomic data to easily accessible databases, or better profiling using genetically encoded protease activity reporters

Arabidopsis thaliana dehydroascorbate reductase 2 : conformational flexibility during catalysis

Dehydroascorbate reductase (DHAR) catalyzes the glutathione (GSH)-dependent reduction of dehydroascorbate and plays a direct role in regenerating ascorbic acid, an essential plant antioxidant vital for defense against oxidative stress. DHAR enzymes bear close structural homology to the glutathione transferase (GST) superfamily of enzymes and contain the same active site motif, but most GSTs do not exhibit DHAR activity. The presence of a cysteine at the active site is essential for the catalytic functioning of DHAR, as mutation of this cysteine abolishes the activity. Here we present the crystal structure of DHAR2 from Arabidopsis thaliana with GSH bound to the catalytic cysteine. This structure reveals localized conformational differences around the active site which distinguishes the GSH-bound DHAR2 structure from that of DHAR1. We also unraveled the enzymatic step in which DHAR releases oxidized glutathione (GSSG). To consolidate our structural and kinetic findings, we investigated potential conformational flexibility in DHAR2 by normal mode analysis and found that subdomain mobility could be linked to GSH binding or GSSG release

The ROS wheel: refining ROS transcriptional footprints

In the last decade, microarray studies have delivered extensive inventories of transcriptome-wide changes in messenger RNA levels provoked by various types of oxidative stress in Arabidopsis (Arabidopsis thaliana). Previous cross-study comparisons indicated how different types of reactive oxygen species (ROS) and their subcellular accumulation sites are able to reshape the transcriptome in specific manners. However, these analyses often employed simplistic statistical frameworks that are not compatible with large-scale analyses. Here, we reanalyzed a total of 79 Affymetrix ATH1 microarray studies of redox homeostasis perturbation experiments. To create hierarchy in such a high number of transcriptomic data sets, all transcriptional profiles were clustered on the overlap extent of their differentially expressed transcripts. Subsequently, meta-analysis determined a single magnitude of differential expression across studies and identified common transcriptional footprints per cluster. The resulting transcriptional footprints revealed the regulation of various metabolic pathways and gene families. The RESPIRATORY BURST OXIDASE HOMOLOG F-mediated respiratory burst had a major impact and was a converging point among several studies. Conversely, the timing of the oxidative stress response was a determining factor in shaping different transcriptome footprints. Our study emphasizes the need to interpret transcriptomic data sets in a systematic context, where initial, specific stress triggers can converge to common, aspecific transcriptional changes. We believe that these refined transcriptional footprints provide a valuable resource for assessing the involvement of ROS in biological processes in plants

Are metacaspases caspases?

The identification of caspases as major regulators of apoptotic cell death in animals initiated a quest for homologous peptidases in other kingdoms. With the discovery of metacaspases in plants, fungi, and protozoa, this search had apparently reached its goal. However, there is compelling evidence that metacaspases lack caspase activity and that they are not responsible for the caspaselike activities detected during plant and fungal cell death. In this paper, we attempt to broaden the discussion of these peptidases to biological functions beyond apoptosis and cell death. We further suggest that metacaspases and paracaspases, although sharing structural and mechanistic features with the metazoan caspases, form a distinct family of clan CD cysteine peptidases

Mitochondrial and chloroplast stress responses are modulated in distinct touch and chemical inhibition phases

Previous studies have identified a range of transcription factors that modulate retrograde regulation of mitochondrial and chloroplast functions in Arabidopsis (Arabidopsis thaliana). However, the relative importance of these regulators and whether they act downstream of separate or overlapping signaling cascades is still unclear. Here, we demonstrate that multiple stress-related signaling pathways, with distinct kinetic signatures, converge on overlapping gene sets involved in energy organelle function. The transcription factor ANAC017 is almost solely responsible for transcript induction of marker genes around 3 to 6 h after chemical inhibition of organelle function and is a key regulator of mitochondrial and specific types of chloroplast retrograde signaling. However, an independent and highly transient gene expression phase, initiated within 10 to 30 min after treatment, also targets energy organelle functions, and is related to touch and wounding responses. Metabolite analysis demonstrates that this early response is concurrent with rapid changes in tricarboxylic acid cycle intermediates and large changes in transcript abundance of genes encoding mitochondrial dicarboxylate carrier proteins. It was further demonstrated that transcription factors AtWRKY15 and AtWRKY40 have repressive regulatory roles in this touch-responsive gene expression. Together, our results show that several regulatory systems can independently affect energy organelle function in response to stress, providing different means to exert operational control