Organelle Extensions in Plant Cells

Cell walls lock each cell in a specific position within the supra-organization of a plant. Despite its fixed location, each cell must be able to sense alterations in its immediate environment and respond rapidly to ensure the optimal functioning, continued growth and development, and eventual long-term survival of the plant. The ultra-structural detail that underlies our present understanding of the plant cell has largely been acquired from fixed and processed material that does not allow an appreciation of the dynamic nature of sub-cellular events in the cell. In recent years, fluorescent protein-aided imaging of living plant cells has added to our understanding of the dynamic nature of the plant cell. One of the major outcomes of live imaging of plant cells is the growing appreciation that organelle shapes are not fixed, and many organelles extend their surface transiently in rapid response to environmental stimuli. In many cases, the extensions appear as tubules extending from the main organelle. Specific terms such as stromules from plastids, matrixules from mitochondria, and peroxules from peroxisomes have been coined to describe the extensions. Here, we review our present understanding of organelle extensions and discuss how they may play potential roles in maintaining cellular homeostasis in plant cells.     

Beginning to understand autophagy, an intracellular self-degradation system in plants

Autophagy is an evolutionarily conserved intracellular process for the vacuolar degradation of cytoplasmic components. There is no doubt that autophagy is very important to plant life, especially because plants are immobile and must survive in environmental extremes. Early studies of autophagy provided our first insights into the structural characteristics of the process in plants, but for a long time the molecular mechanisms and the physiological roles of autophagy were not understood. Genetic analyses of autophagy in the yeast Saccharomyces cerevisiae have greatly expanded our knowledge of the molecular aspects of autophagy in plants as well as in animals. Until recently our knowledge of plant autophagy was in its infancy compared with autophagy research in yeast and animals, but recent efforts by plant researchers have made many advances in our understanding of plant autophagy. Here I will introduce an overview of autophagy in plants, present current findings and discuss the physiological roles of self-degradation.     

The plant cell wall: Biosynthesis,construction, and functions

The plant cell wall is composed of multiple biopolymers, representing one of the most complex structural networks in nature. Hundreds of genes are involved in building such a natural masterpiece. However, the plant cell wall is the least understood cellular structure in plants. Due to great progress in plant functional genomics,manyachievementshavebeenmadein uncovering cell wall biosynthesis, assembly, and architecture, as well as cell wall regulation and signaling. Such information has significantly advanced our understanding of the roles of the cell wall in many biological and physiological processes and has enhanced our utilization of cell wall materials. The use of cutting-edge technologies such as single-molecule imaging,nuclear magnetic resonance spectroscopy, and atomic force microscopy has provided much insight into the plant cell wall as an intricate nanoscale network, opening up unprecedented possibilities for cell wall research. In this review,we summarize the major advances made in understanding the cell wall in this era of functional genomics, including the latest findings on the biosynthesis, construction, and functions of the cell wall.     

Flavonoids:New Roles for Old Molecules

Flavonoids are ubiquitous in the plant kingdom and have many diverse functions including defense, UV protection, auxin transport inhibition, allelopathy, and flower coloring. Interestingly, these compounds also have considerable biological activity in plant, animal and bacterial systems – such broad activity is accomplished by few compounds. Yet, for all the research over the last three decades, many of the cellular targets of these secondary metabolites are unknown. The many mutants available in model plant species such as Arabidopsis thaliana and Medicago truncatula are enabling the intricacies of the physiology of these compounds to be deduced. In the present review, we cover recent advances in flavonoid research, discuss deficiencies in our understanding of the physiological processes, and suggest approaches to identify the cellular targets of flavonoids.     

Indirect defence of plants against herbivores: using Arabidopsis thaliana as a model plant

In their defence against pathogens, herbivorous insects, and mites, plants employ many induced responses. One of these responses is the induced emission of volatiles upon herbivory. These volatiles can guide predators or parasitoids to their herbivorous prey, and thus benefit both plant and carnivore. This use of carnivores by plants is termed indirect defence and has been reported for many plant species, including elm, pine, maize, Lima bean, cotton, cucumber, tobacco, tomato, cabbage, and Arabidopsis thaliana. Herbivory activates an intricate signalling web and finally results in defence responses such as increased production of volatiles. Although several components of this signalling web are known (for example the plant hormones jasmonic acid, salicylic acid, and ethylene), our understanding of how these components interact and how other components are involved is still limited. Here we review the knowledge on elicitation and signal transduction of herbivory-induced volatile production. Additionally, we discuss how use of the model plant Arabidopsis thaliana can enhance our understanding of signal transduction in indirect defence and how cross-talk and trade-offs with signal transduction in direct defence against herbivores and pathogens influences plant responses.     

Ion-selective Microelectrodes: Their Use and Importance in Modern Plant Cell Biology

The exact ion gradients across cellular membranes and their changes due to metabolic or transport processes can be best studied with the use of ion-selective microelectrodes. The last decade of research using ion-selective microelectrodes in intact cells has proven this technique to be indispensable for the investigation of a variety of physiological questions of regulatory processes, membrane transport, cellular signalling, developmental biology and plant nutrition. Their application to selected problems has led to numerous exciting observations, many of which have changed our view concerning cellular responses to environmental stimuli and in many instances have led to a new understanding of plant cell physiology. Since, with these electrodes, intracellular as well as extracellular free ion concentrations can be simultaneously detected with electrical transport parameters such as membrane potential and membrane conductance, they can be powerful tools in the hands of many plant cell biologists.     

Inositol phospholipid metabolism in Arabidopsis. Characterized and putative isoforms of inositol phospholipid kinase and phosphoinositide-specific phospholipase C

Phosphoinositides (PIs) constitute a minor fraction of total cellular lipids in all eukaryotic cells. They fulfill many important functions through interaction with a wide range of cellular proteins. Members of distinct inositol lipid kinase families catalyze the synthesis of these phospholipids from phosphatidylinositol. The hydrolysis of PIs involves phosphatases and isoforms of PI-specific phospholipase C. Although our knowledge of the roles played by plant PIs is clearly limited at present, there is no doubt that they are involved in many physiological processes during plant growth and development. In this review, we concentrate on inositol lipid-metabolizing enzymes from the model plant Arabidopsis for which biochemical characterization data are available, namely the inositol lipid kinases and PI-specific phospholipase Cs. The biochemical properties and structure of characterized and genome-predicted isoforms are presented and compared with those of the animal enzymes to show that the plant enzymes have some features clearly unique to this kingdom.     

Conventional and unconventional ubiquitination in plant immunity

Ubiquitination is one of the most abundant types of protein post‐translational modification (PTM) in plant cells. The importance of ubiquitination in the regulation of many aspects of plant immunity has been increasingly appreciated in recent years. Most of the studies linking ubiquitination to the plant immune system, however, have been focused on the E3 ubiquitin ligases and the conventional ubiquitination that leads to the degradation of the substrate proteins by the 26S proteasome. By contrast, our knowledge about the role of unconventional ubiquitination that often serves as non‐degradative, regulatory signal remains a significant gap. We discuss, in this review, the recent advances in our understanding of ubiquitination in the modulation of plant immunity, with a particular focus on the E3 ubiquitin ligases. We approach the topic from a perspective of two broadly defined types of ubiquitination in an attempt to highlight the importance, yet current scarcity, in our knowledge about the regulation of plant immunity by unconventional ubiquitination.     

From bench to bountiful harvests: a road map for the next decade of Arabidopsis research

In the face of an increasing world population and climate instability, the demands for food and fuel will continue to rise. Plant science will be crucial to help meet these exponentially increasing requirements for food and fuel supplies. Fundamental plant research will play a major role in providing key advances in our understanding of basic plant processes that can then flow into practical advances through knowledge sharing and collaborations. The model plant Arabidopsis thaliana has played a major role in our understanding of plant biology, and the Arabidopsis community has developed many tools and resources to continue building on this knowledge. Drawing from previous experience of internationally coordinated projects, The international Arabidopsis community, represented by the Multinational Arabidopsis Steering Committee (MASC), has drawn up a road map for the next decade of Arabidopsis research to inform scientists and decision makers on the future foci of Arabidopsis research within the wider plant science landscape. This article provides a summary of the MASC road map.     

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

Plant litter may play an important role in herbaceous plant communities by limiting primary production and influencing plant species richness. However, it is not known how the effect of litter interacts with fertilization. We tested for the role of litter and fertilization in a large-scale experiment to investigate effects on diversity and biomass of plant species, growth forms, native vs. non-native groups, and abiotic ecosystem components (e.g., soil moisture, PAR). We manipulated plant litter (removed vs. left in situ) and nutrient availability (NPK-fertilized vs. unfertilized) for 4 years in 314-m² plots, replicated six times, in an old-field grassland. While many of our species-level results supported previously published studies and theory, our plant group results generally did not. Specifically, grass species richness and forb biomass was not affected by either fertilization or plant litter. Moreover, plant litter removal significantly increased non-native plant species richness. Relative to native plant species, all of our experimental manipulations significantly increased both the biomass and the species richness of non-native plant species. Thus, this grassland system was sensitive to management treatments through the facilitation of non-native plant species. We coupled biotic and abiotic components within a nonmetric multidimensional scaling (NMS) analysis to investigate treatment effects, which revealed that specific treatments altered ecosystem development. These results suggest that fertilization and plant litter may have larger impacts on plant communities and on ecosystem properties than previously understood, underscoring the need for larger-scale and longer-term experiments.     

Small RNAs: Efficient and miraculous effectors that play key roles in plant–microbe interactions

Plants' response to pathogens is highly complex and involves changes at different levels, such as activation or repression of a vast array of genes. Recently, many studies have demonstrated that many RNAs, especially small RNAs (sRNAs), are involved in genetic expression and reprogramming affecting plant–pathogen interactions. The sRNAs, including short interfering RNAs and microRNAs, are noncoding RNA with 18–30 nucleotides, and are recognized as key genetic and epigenetic regulators. In this review, we summarize the new findings about defence-related sRNAs in the response to pathogens and our current understanding of their effects on plant–pathogen interactions. The main content of this review article includes the roles of sRNAs in plant–pathogen interactions, cross-kingdom sRNA trafficking between host and pathogen, and the application of RNA-based fungicides for plant disease control.     

Effects of polyploidization on the contents of photosynthetic pigments are largely population-specific

Photosynthesis Research - The contents of photosynthetic pigments are an important indicator of many processes taking place in the plant body. Still, however, our knowledge of the effects of...     

Plant enzymes but not Agrobacterium VirD2 mediate T-DNA ligation in vitro

Agrobacterium tumefaciens, a gram-negative soil bacterium, transfers DNA to many plant species. In the plant cell, the transferred DNA (T-DNA) is integrated into the genome. An in vitro ligation-integration assay has been designed to investigate the mechanism of T-DNA ligation and the factors involved in this process. The VirD2 protein, which is produced in Agrobacterium and is covalently attached to T-DNA, did not, under our assay conditions, ligate T-DNA to a model target sequence in vitro. We tested whether plant extracts could ligate T-DNA to target oligonucleotides in our test system. The in vitro ligation-integration reaction did indeed take place in the presence of plant extracts. This reaction was inhibited by dTTP, indicating involvement of a plant DNA ligase. We found that prokaryotic DNA ligases could substitute for plant extracts in this reaction. Ligation of the VirD2-bound oligonucleotide to the target sequence mediated by T4 DNA ligase was less efficient than ligation of a free oligonucleotide to the target. T-DNA ligation mediated by a plant enzyme(s) or T4 DNA ligase requires ATP.     

The modulating effect of bacterial volatiles on plant growth: Current knowledge and future challenges

Bacteria interact with plants in many different ways. In recent years, bacterial production of volatiles has emerged as a novel process by which bacteria modulate plant growth. Exposure to the volatiles produced by certain bacterial strains has been shown to lead to up to 5-fold increased plant biomass or to plant death. Despite these drastic growth alterations, the elucidation of the molecules responsible, of the mechanisms of perception by the plant and of the specific metabolic changes induced in planta is still in its infancy. This review summarizes the current knowledge and highlights future lines of research that should increase our knowledge of the volatile-mediated dialog between bacteria and plants.     

Satish Chandra Maheshwari (1933–2019)—a brilliant,passionate and an outstanding shining light for all of plant biology

Physiology and Molecular Biology of Plants - We present here a tribute to Satish Chandra Maheshwari (known to many as SCM, or simply Satish), one of the greatest plant biologists of our time. He...