Xyloglucan deficiency leads to a reduction in turgor pressure and changes in cell wall properties, affecting early seedling establishment.

Xyloglucan is believed to play a significant role in cell wall mechanics of dicot plants. Surprisingly, Arabidopsis plants defective in xyloglucan biosynthesis exhibit nearly normal growth and development. We investigated a mutant line, cslc-Δ5, lacking activity in all five Arabidopsis cellulose synthase like-C (CSLC) genes responsible for xyloglucan backbone biosynthesis. We observed that this xyloglucan-deficient line exhibited reduced cellulose crystallinity and increased pectin levels, suggesting the existence of feedback mechanisms that regulate wall composition to compensate for the absence of xyloglucan. These alterations in cell wall composition in the xyloglucan-absent plants were further linked to a decrease in cell wall elastic modulus and rupture stress, as observed through atomic force microscopy (AFM) and extensometer-based techniques. This raised questions about how plants with such modified cell wall properties can maintain normal growth. Our investigation revealed two key factors contributing to this phenomenon. First, measurements of turgor pressure, a primary driver of plant growth, revealed that cslc-Δ5 plants have reduced turgor, preventing the compromised walls from bursting while still allowing growth to occur. Second, we discovered the conservation of elastic asymmetry (ratio of axial to transverse wall elasticity) in the mutant, suggesting an additional mechanism contributing to the maintenance of normal growth. This novel feedback mechanism between cell wall composition and mechanical properties, coupled with turgor pressure regulation, plays a central role in the control of plant growth and is critical for seedling establishment in a mechanically challenging environment by affecting shoot emergence and root penetration.

Flip-Flap: A Simple Dual-View Imaging Method for 3D Reconstruction of Thick Plant Samples.

Plant development is a complex process that relies on molecular and cellular events being co-ordinated in space and time. Microscopy is one of the most powerful tools available to investigate this spatiotemporal complexity. One step towards a better understanding of complexity in plants would be the acquisition of 3D images of entire organs. However, 3D imaging of intact plant samples is not always simple and often requires expensive and/or non-trivial approaches. In particular, the inner tissues of thick samples are challenging to image. Here, we present the Flip-Flap method, a simple imaging protocol to produce 3D images of cleared plant samples at the organ scale. This method allows full 3D reconstruction of plant organs suitable for 3D segmentation and further related analysis and can be easily handled by relatively inexperienced microscopists.

Plant cell divisions: variations from the shortest symmetric path.

In plants, the spatial arrangement of cells within tissues and organs is a direct consequence of the positioning of the new cell walls during cell division. Since the nineteenth century, scientists have proposed rules to explain the orientation of plant cell divisions. Most of these rules predict the new wall will follow the shortest path passing through the cell centroid halving the cell into two equal volumes. However, in some developmental contexts, divisions deviate significantly from this rule. In these situations, mechanical stress, hormonal signalling, or cell polarity have been described to influence the division path. Here we discuss the mechanism and subcellular structure required to define the cell division placement then we provide an overview of the situations where division deviates from the shortest symmetric path.

Spatiotemporal control of cell growth by CUC3 shapes leaf margins.

How a shape arises from the coordinated behavior of cells is one of the most fascinating questions in developmental biology. In plants, fine spatial and temporal controls of cell proliferation and cell expansion sustain differential growth that defines organ shape and size. At the leaf margin of Arabidopsis thaliana, interplay between auxin transport and transcription factors named CUP SHAPED COTYLEDON (CUCs), which are involved in the establishment of boundary domain identity, were reported to trigger differential growth, leading to serration. Cellular behaviors behind these differential growths remain scarcely described. Here, we used 3D and time lapse imaging on young leaves at different stages of development to determine the sequence of cellular events resulting in leaf serrations. In addition, we showed that the transcription factor CUC3 is a negative regulator of cell growth and that its expression dynamics in a small number of cells at the leaf margin is tightly associated with the control of differential growth.

Heterogeneity and its multiscale integration in plant morphogenesis.

Heterogeneity is observed at all levels in living organisms, but its role during the development of an individual is not well understood. Heterogeneity has either to be limited to ensure robust development or can be an actor of the biological processes leading to reproducible development. Here we review the sources of heterogeneity in plants, stress the interplay between noise in elementary processes and regulated biological mechanisms, and highlight how heterogeneity is integrated at multiple scales during plant morphogenesis.