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Arabidopsis synaptotagmin 1 (SYT1) is localized on the endoplasmic reticulum–plasma membrane (ER–PM) contact sites in leaf and root cells. The ER–PM localization of Arabidopsis SYT1 resembles that of the extended synaptotagmins (E-SYTs) in animal cells. In mammals, E-SYTs have been shown to regulate calcium signaling, lipid transfer, and endocytosis. Arabidopsis SYT1 was reported to be essential for maintaining cell integrity and virus movement. This study provides detailed insight into the subcellular localization of SYT1 and VAP27-1, another ER–PM-tethering protein. SYT1 and VAP27-1 were shown to be localized on distinct ER–PM contact sites. The VAP27-1-enriched ER–PM contact sites (V-EPCSs) were always in contact with the SYT1-enriched ER–PM contact sites (S-EPCSs). The V-EPCSs still existed in the leaf epidermal cells of the SYT1 null mutant; however, they were less stable than those in the wild type. The polygonal networks of cortical ER disassembled and the mobility of VAP27-1 protein on the ER–PM contact sites increased in leaf cells of the SYT1 null mutant. These results suggest that SYT1 is responsible for stabilizing the ER network and V-EPCSs.

Being sessile organisms that need to effectively explore space (above and below ground) and acquire resources through growth, plants must simultaneously consider multiple possibilities and wisely balance the energy they spend on growth with the benefits for survival [...]

Nitric oxide (NO), a non-charged, small, gaseous free-radical, is a signaling molecule in all plant cells. Several studies have proposed multifarious physiological roles for NO, from seed germination to plant maturation and senescence. Nitric oxide is thought to act as an antioxidant, quenching ROS during oxidative stress and reducing lipid peroxidation. NO also mediates photosynthesis and stomatal conductance and regulates programmed cell death, thus providing tolerance to abiotic stress. In mitochondria, NO participates in the electron transport pathway. Nitric oxide synthase and nitrate reductase are the key enzymes involved in NO-biosynthesis in aerobic plants, but non-enzymatic pathways have been reported as well. Nitric oxide can interact with a broad range of molecules, leading to the modification of protein activity, GSH biosynthesis, S-nitrosylation, peroxynitrite formation, proline accumulation, etc., to sustain stress tolerance. In addition to these interactions, NO interacts with fatty acids to form nitro-fatty acids as signals for antioxidant defense. Polyamines and NO interact positively to increase polyamine content and activity. A large number of genes are reprogrammed by NO; among these genes, proline metabolism genes are upregulated. Exogenous NO application is also shown to be involved in salinity tolerance and/or resistance via growth promotion, reversing oxidative damage and maintaining ion homeostasis. This review highlights NO-mediated salinity-stress tolerance in plants, including NO biosynthesis, regulation, and signaling. Nitric oxide-mediated ROS metabolism, antioxidant defense, and gene expression and the interactions of NO with other bioactive molecules are also discussed. We conclude the review with a discussion of unsolved issues and suggestions for future research.

Controlled plant growth requires regulation through a variety of signaling molecules, including steroids, peptides, radicals of oxygen and nitrogen, as well as the ‘classical’ phytohormone groups. Auxin is critical for the control of plant growth and also orchestrates many developmental processes, such as the formation of new roots. It modulates root architecture both slowly, through actions at the transcriptional level and, more rapidly, by mechanisms targeting primarily plasma membrane sensory systems and intracellular signaling pathways. The latter reactions use several second messengers, including Ca2+, nitric oxide (NO) and reactive oxygen species (ROS). Here, we investigated the different roles of two auxins, the major auxin indole-3-acetic acid (IAA) and another endogenous auxin indole-3-butyric acid (IBA), in the lateral root formation process of Arabidopsis and maize. This was mainly analyzed by different types of fluorescence microscopy and inhibitors of NO production. This study revealed that peroxisomal IBA to IAA conversion is followed by peroxisomal NO, which is important for IBA-induced lateral root formation. We conclude that peroxisomal NO emerges as a new player in auxin-induced root organogenesis. In particular, the spatially and temporally coordinated release of NO and IAA from peroxisomes is behind the strong promotion of lateral root formation via IBA.

Interactions between individuals that are guided by simple rules can generate swarming behavior. Swarming behavior has been observed in many groups of organisms, including humans, and recent research has revealed that plants also demonstrate social behavior based on mutual interaction with other individuals. However, this behavior has not previously been analyzed in the context of swarming. Here, we show that roots can be influenced by their neighbors to induce a tendency to align the directions of their growth. In the apparently noisy patterns formed by growing roots, episodic alignments are observed as the roots grow close to each other. These events are incompatible with the statistics of purely random growth. We present experimental results and a theoretical model that describes the growth of maize roots in terms of swarming.

Background Cell Theory, also known as cell doctrine, states that all eukaryotic organisms are composed of cells, and that cells are the smallest independent units of life. This Cell Theory has been influential in shaping the biological sciences ever since, in 1838/1839, the botanist Matthias Schleiden and the zoologist Theodore Schwann stated the principle that cells represent the elements from which all plant and animal tissues are constructed. Some 20 years later, in a famous aphorism Omnis cellula e cellula, Rudolf Virchow annunciated that all cells arise only from pre-existing cells. General acceptance of Cell Theory was finally possible only when the cellular nature of brain tissues was confirmed at the end of the 20th century. Cell Theory then rapidly turned into a more dogmatic cell doctrine, and in this form survives up to the present day. In its current version, however, the generalized Cell Theory developed for both animals and plants is unable to accommodate the supracellular nature of higher plants, which is founded upon a super-symplasm of interconnected cells into which is woven apoplasm, symplasm and super-apoplasm. Furthermore, there are numerous examples of multinucleate coenocytes and syncytia found throughout the eukaryote superkingdom posing serious problems for the current version of Cell Theory. Scope To cope with these problems, we here review data which conform to the original proposal of Daniel Mazia that the eukaryotic cell is composed of an elemental Cell Body whose structure is smaller than the cell and which is endowed with all the basic attributes of a living entity. A complement to the Cell Body is the Cell Periphery Apparatus, which consists of the plasma membrane associated with other periphery structures. Importantly, boundary stuctures of the Cell Periphery Apparatus, although capable of some self-assembly, are largely produced and maintained by Cell Body activities and can be produced from it de novo. These boundary structures serve not only as mechanical support for the Cell Bodies but they also protect them from the hostile external environment and from inappropriate interactions with adjacent Cell Bodies within the organism. Conclusions From the evolutionary perspective, Cell Bodies of eukaryotes are proposed to represent vestiges of hypothetical, tubulin-based 'guest' proto-cells. After penetrating the equally hypothetical actin-based 'host' proto-cells, tubulin-based 'guests' became specialized for transcribing, storing and partitioning DNA molecules via the organization of microtubules. The Cell Periphery Apparatus, on the other hand, represents vestiges of the actin-based 'host' proto-cells which have become specialized for Cell Body protection, shape control, motility and for actin-mediated signalling across the plasma membrane.

Vascular plants are integrated into coherent bodies via plant-specific synaptic adhesion domains, action potentials (APs) and other means of long-distance signalling running throughout the plant bodies. Plant-specific synapses and APs are proposed to allow plants to generate their self identities having unique ways of sensing and acting as agents with their own goals guiding their future activities. Plants move their organs with a purpose and with obvious awareness of their surroundings and require APs to perform and control these movements. Self-identities allow vascular plants to act as individuals enjoying sociality via their self/non-self-recognition and kin recognition. Flowering plants emerge as cognitive and intelligent organisms when the major strategy is to attract and control their animal pollinators as well as seed dispersers by providing them with food enriched with nutritive and manipulative/addictive compounds. Their goal in interactions with animals is manipulation for reproduction, dispersal and defence. This article is part of the theme issue ‘Basal cognition: multicellularity, neurons and the cognitive lens’.

Autophagy is a eukaryotic catabolic pathway essential for growth and development. In plants, it is activated in response to environmental cues or developmental stimuli. However, in contrast to other eukaryotic systems, we know relatively little regarding the molecular players involved in autophagy and the regulation of this complex pathway. In the framework of the COST (European Cooperation in Science and Technology) action TRANSAUTOPHAGY (2016-2020), we decided to review our current knowledge of autophagy responses in higher plants, with emphasis on knowledge gaps. We also assess here the potential of translating the acquired knowledge to improve crop plant growth and development in a context of growing social and environmental challenges for agriculture in the near future.

Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone.

Background and Aim The cytoskeleton plays an important role in the synthesis of plant cell walls. Both microtubules and actin cytoskeleton are known to be involved in the morphogenesis of plant cells through their role in cell wall building. The role of ARP2/3-nucleated actin cytoskeleton in the morphogenesis of cotyledon pavement cells has been described before. Seedlings of A rabidopsis mutants lacking a functional ARP2/3 complex display specific cell wall-associated defects. Methods In three independent Arabidopsis mutant lines lacking subunits of the ARP2/3 complex. phenotypes associated with the loss of the complex were analysed throughout plant development. Organ size and anatomy, cell wall composition. and auxin distribution were investigated. Key Results ARP2/3-related phenotype is associated with changes in cell wall composition, and the phenotype is manifested especially in mature tissues. Cell walls of mature plants contain less cellulose and a higher amount of homogalacturonan, and display changes in cell wall lignification. Vascular bundles of mutant inflorescence stems show a changed pattern of AUX1-YFP expression. Plants lacking a functional ARP2/3 complex have decreased basipetal auxin transport. Conclusions The results suggest that the ARP2/3 complex has a morphogenetic function related to cell wall synthesis and auxin transport.