Current Opinion in Plant Biology

Plants have a remarkable regenerative capacity, but it varies widely among species and tissue types. Whether plant cells/tissues initiate regeneration largely depends on the extent to which they are constrained to their original tissue fate. Once cells start the regeneration program, they acquire a new fate, form meristems, and develop into organs. During these processes, the cells must continuously overcome various barriers to the progression of the regeneration program until the organ (or whole plant) is complete...

The green plants (Viridiplantae) are an essential kingdom of life, responsible via photosynthesis for the majority of global primary production, and directly utilized by humankind for nutrition, animal feed, fuel, clothing, medicine and other purposes. There are an estimated 391 000 species of land plants, in addition to 8000 species of green algae. Their genomes are unusually diverse compared to those of other kingdoms, ranging in size from ∼10 Mb to over 100 Gb. Knowledge of plant genomes initially lagged behind those of other kingdoms but has greatly increased with the development of new technologies for DNA sequencing; bioinformatic analysis, rather than data production, is increasingly the bottleneck to further knowledge...

The formation of spatial and temporal patterns is an essential component of organismal development. Patterns can be observed on every level from subcellular to organismal and may emerge from local rules that correspond to the interactions between molecules, cells, or tissues. The emergence of robust patterns may seem in contradiction with the prominent heterogeneity at subcellular and cellular scales, however it has become increasingly clear that heterogeneity can be instrumental for pattern formation. Here we review recent examples in plant development, involving genetic regulation, cell arrangement, growth and signal gradient...

Mapping fossil traits onto the land plant phylogenetic framework indicates that there were at least two independent origins of roots among extant vascular plants - once in lycophytes and independently in euphyllophytes. At least two rooting structural types are found among extinct species preserved in the Rhynie chert. First, species that lacked roots and developed horizontal axes that developed rhizoids. Second, the rooting axes of Asteroxylon mackiei resembled the roots of extant lycopsids but lacked root hairs and root caps...

Coordination between plant development and nutrient availability ensures a suitable supply of macromolecules for growth and developmental programs. Nitrate is an important source of nitrogen (N) that acts as a signal molecule to modulate gene expression, physiological, growth and developmental responses throughout the life of the plant. New key players in the nitrate signaling pathway have been described and knowledge of the molecular mechanics of how it impacts growth and developmental processes is increasing fast...

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The cellular responses to abiotic and biotic stress rely on the regulation of vesicle trafficking to ensure the correct localization of proteins specialized in sensing stress stimuli and effecting the response. Several studies have implicated the plant trans-Golgi network (TGN)-mediated trafficking in different types of biotic and abiotic stress responses; however, the underlying molecular mechanisms are poorly understood. Further, the identity, specialization and stress-relevant cargo transported by the TGN subcompartments involved in stress responses await more in depth characterization...

Autophagy mediates the delivery of cytoplasmic content to vacuoles or lysosomes for degradation or storage. The best characterized autophagy route called macroautophagy involves the sequestration of cargo in double-membrane autophagosomes and is conserved in eukaryotes, including plants. Recently, several new receptors, some of them plant-specific, that select cargo for macroautophagy have been identified. Some of these receptors appear to participate in regulation of competing catabolic pathways, for example proteasome-mediated versus autophagic degradation under specific stress conditions...

Recently, the plant transport field has shifted their research focus toward a more integrative investigation of transport networks thought to provide the basis for long-range transport routes. Substantial progress was provided by of a series of elegant techniques that allow for a visualization or prediction of substrate movements in plant tissues in contrast to established quantitative methods offering low spatial resolution. These methods are critically evaluated in respect to their spatio-temporal resolution, invasiveness, dynamics and overall quality...

The unicellular green alga Chlamydomonas provides a simplified model for defining core cell cycle functions conserved in the green lineage and for understanding multiple fission, a common cell cycle variation found in many algae. Systems-level approaches including a recent groundbreaking screen for conditional lethal cell cycle mutants and genome-wide transcriptome analyses are revealing the complex relationships among cell cycle regulators and helping define roles for CDKA/CDK1 and CDKB, the latter of which is unique to the green lineage and plays a central role in mitotic regulation...

This article briefly reviews recent advances in nano-scale and micro-scale assessments of primary cell wall structure, mechanical behaviors and expansive growth. Cellulose microfibrils have hydrophobic and hydrophilic faces which may selectively bind different matrix polysaccharides and adjacent microfibrils. These distinctive binding interactions may guide partially aligned cellulose microfibrils in primary cell walls to form a planar, load-bearing network within each lamella of polylamellate walls. Consideration of expansive growth of cross-lamellate walls leads to a surprising inference: side-by-side sliding of microfibrils may be a key rate-limiting physical step, potentially targeted by specific wall loosening agents...

Salt stress results in a dramatic increase in ABA biosynthesis, H2 O2 accumulation, and reduced K+ availability in the shoot. Each of these factors leads to stomata closure, so reducing CO2 assimilation and imposing yield penalties. However, halophytes, naturally salt tolerant plant species, flourish under saline conditions that would cause massive yield penalties in glycophytic crops. Is there anything special about the stomata of halophytes, why is guard cell function in these salt tolerant species not affected by the above factors? This opinion paper addresses these questions by providing a comprehensive assessment of the molecular identity and operational modes of major plasma membrane transporters that mediate stomata movements...

Membrane-embedded transport proteins are fundamental to life; their co-ordinated action controls the movement and distribution of solutes into, around and out of cells for signalling, metabolism, nutrition, stress tolerance and development. Here we outline two case studies of transport systems that plants use to tolerate soil elemental toxicity, demonstrating how iterative studies of protein structure and function result in unparalleled insights into transport mechanics. Further, we propose that integrative platforms of biological, biochemical and biophysical tools can provide quantitative data on substrate specificity and transport rates, which are important in understanding transporter evolution and their roles in cell biology and whole plant physiology...

Assembly of polysaccharide-based walls by plant cells involves the rapid synthesis, trafficking, and deposition of complex biopolymers, but how these events are controlled and coordinated to achieve a strong, resilient extracellular matrix has remained obscure for decades. Recent quantitative analyses of fluorescence microscopy data have revealed details of the trafficking and synthetic activity of cellulose synthases, and new methods for labeling matrix polymers have unveiled aspects of their regulated deposition in the wall...

Optical tweezers enable users to physically trap organelles and move them laterally within the plant cell. Recent advances have highlighted physical interactions between functionally related organelle pairs, such as ER-Golgi and peroxisome-chloroplast, and have shown how organelle positioning affects plant growth. Quantification of these processes has provided insight into the force components which ultimately drive organelle movement and positioning in plant cells. Application of optical tweezers has therefore revolutionised our understanding of plant organelle dynamics...

The phragmoplast is a plant-specific secretory module that partitions daughter cells during cytokinesis by constructing a cell plate from membranes and oligosaccharides. The cell plate is typically a long structure, which requires the phragmoplast to expand to complete cytokinesis. The phragmoplast expands by coordinating microtubule dynamics with membrane trafficking. Each step in phragmoplast expansion involves the establishment of anti-parallel microtubule overlaps that are enriched with the protein MAP65, which recruits cytokinetic vesicles through interaction with the tethering factor, TRAPPII...

Plastids undergo drastic shape changes under stress, including the formation of stroma-filled tubules, or `stromules'. Stromules are dynamic, and may extend, branch and retract within minutes. There are two prerequisites for stromule extension: excess plastid membrane and a force(s) that shapes the membrane into a tubule. In vitro studies provide insight into the basic molecular machinery for tubulation, and are often cited when discussing stromule formation. In this review, we evaluate in vitro modes of tubulation in the context of stromule dynamics, and find that most mechanisms fail to explain stromule morphology and behavior observed in planta...

Fluorescent protein-based biosensors are providing us with an unprecedented, quantitative view of the dynamic nature of the cellular networks that lie at the heart of plant biology. Such bioreporters can visualize the spatial and temporal kinetics of cellular regulators such as Ca2+ and H+ , plant hormones and even allow membrane transport activities to be monitored in real time in living plant cells. The fast pace of their development is making these tools increasingly sensitive and easy to use and the rapidly expanding biosensor toolkit offers great potential for new insights into a wide range of plant regulatory processes...

Research on mosses has provided answers to many fundamental questions in the life sciences, with the model moss Physcomitrella patens spearheading the field. Recent breakthroughs in cell biology were obtained in the quantification of chlorophyll fluorescence, signalling via calcium waves, the creation of designer organelles, gene identification in cellular reprogramming, reproduction via motile sperm and egg cells, asymmetric cell division, visualization of the actin cytoskeleton, identification of genes responsible for the shift from 2D to 3D growth, the structure and importance of the cell wall, and in the live imaging and modelling of protein networks in general...

The process of shape change in cells and tissues inevitably involves the modification of structural elements, therefore it is necessary to integrate mechanics with biochemistry to develop a full understanding of morphogenesis. Here, we discuss recent findings on the role of biomechanics and biochemical processes in plant cell growth and development. In particular, we focus on how the plant cytoskeleton components, which are known to regulate morphogenesis, are influenced by biomechanical stress. We also discuss new insights into the role that pectin plays in biomechanics and morphogenesis...