A network-based framework for shape analysis enables accurate characterization of leaf epidermal cells.

Cell shape is crucial for the function and development of organisms. Yet, versatile frameworks for cell shape quantification, comparison, and classification remain underdeveloped. Here, we introduce a visibility graph representation of shapes that facilitates network-driven characterization and analyses across shapes encountered in different domains. Using the example of complex shape of leaf pavement cells, we show that our framework accurately quantifies cell protrusions and invaginations and provides additional functionality in comparison to the contending approaches. We further show that structural properties of the visibility graphs can be used to quantify pavement cell shape complexity and allow for classification of plants into their respective phylogenetic clades. Therefore, the visibility graphs provide a robust and unique framework to accurately quantify and classify the shape of different objects.

Long-term live-cell imaging techniques for visualizing pavement cell morphogenesis.

Recent advancements in microscopy and biological technologies have allowed scientists to study dynamic plant developmental processes with high temporal and spatial resolution. Pavement cells, epidermal cells found on leaf tissue, form complex shapes with alternating regions of indentations and outgrowths that are postulated to be driven by the microtubule cytoskeleton. Given their complex shapes, pavement cells and the microtubule contribution towards morphogenesis have been of great interest in the field of developmental biology. Here, we focus on two live-cell imaging methods that allow for early and long-term imaging of the cotyledon (embryonic leaf-like tissue) and leaf epidermis with minimal invasiveness in order to study microtubules throughout pavement cell morphogenesis. The methods described in this chapter can be applied to studying other developmental processes associated with cotyledon and leaf tissue.

Plant Biology: Bending of Plant Organs.

Tissue folding allows for the development of complex three-dimensional morphologies necessary for various functions. A new study provides novel mechanistic insights linking plant cell wall and hormonal pathways involved in bending of plant tissue through regulation of differential growth.

Getting into shape: the mechanics behind plant morphogenesis.

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. Using the jigsaw-shaped pavement cells of the leaf as a case study, we review new findings on the biomechanics behind the morphogenesis of these intricately-shaped cell types. Finally, we summarize important quantitative techniques that has allowed for the testing and the generation of hypotheses that link biomechanics to morphogenesis.

The microtubule plus-end tracking protein ARMADILLO-REPEAT KINESIN1 promotes microtubule catastrophe in Arabidopsis.

Microtubule dynamics are critically important for plant cell development. Here, we show that Arabidopsis thaliana ARMADILLO-REPEAT KINESIN1 (ARK1) plays a key role in root hair tip growth by promoting microtubule catastrophe events. This destabilizing activity appears to maintain adequate free tubulin concentrations in order to permit rapid microtubule growth, which in turn is correlated with uniform tip growth. Microtubules in ark1-1 root hairs exhibited reduced catastrophe frequency and slower growth velocities, both of which were restored by low concentrations of the microtubule-destabilizing drug oryzalin. An ARK1-GFP (green fluorescent protein) fusion protein expressed under its endogenous promoter localized to growing microtubule plus ends and rescued the ark1-1 root hair phenotype. Transient overexpression of ARK1-RFP (red fluorescent protein) increased microtubule catastrophe frequency. ARK1-fusion protein constructs lacking the N-terminal motor domain still labeled microtubules, suggesting the existence of a second microtubule binding domain at the C terminus of ARK1. ARK1-GFP was broadly expressed in seedlings, but mutant phenotypes were restricted to root hairs, indicating that ARK1's function is redundant in cells other than those forming root hairs.