Microtubule-Mediated Wall Anisotropy Contributes to Leaf Blade Flattening

Abstract

Summary Plant organs can adopt a wide range of shapes, resulting from highly directional cell growth and divisions. We focus here on leaves and leaf-like organs in Arabidopsis and tomato, characterized by the formation of thin, flat laminae. Combining experimental approaches with 3D mechanical modeling, we provide evidence that leaf shape depends on cortical microtubule mediated cellulose deposition along the main predicted stress orientations, in particular, along the adaxial-abaxial axis in internal cell walls. This behavior can be explained by a mechanical feedback and has the potential to sustain and even amplify a preexisting degree of flatness, which in turn depends on genes involved in the control of organ polarity and leaf margin formation.

Visualization of cortical microtubule networks in plant cells by live imaging and immunostaining

“…CMT bundles associated with GFP-MBD can be visualized in the epidermal cells of the abaxial side of Arabidopsis sepal primordium ( Figures 3 A and 3B). The orientation of CMTs depends on the developmental stages of sepal primordium ( Zhao et al., 2020 ).…”

“…Labeling of CMTs in cells of inner tissues can be successfully achieved through immunostaining of agarose-gel sections ( Kitaeva et al., 2016 ; Zhao et al., 2020 ). In the cross-sections of tomato leaf primordia, α-tubulin antibodies bind to the CMTs along the anticlinal cell walls.…”

“…In the cross-sections of tomato leaf primordia, α-tubulin antibodies bind to the CMTs along the anticlinal cell walls. The overall organization of CMTs in majority of cells displays a highly anisotropic arrangement, in which the orientation of CMT bundles is parallel to the adaxial-abaxial axis ( Figures 3 C and 3D) ( Zhao et al., 2020 ).…”

“…CMT networks in the outer tissue layers can be directly visualized by live imaging of a fluorescent reporter line, and a protocol combining sectioning and immunostaining is applied for visualization of CMTs throughout tissues. For complete details on the use and execution of this protocol, please refer to Zhao et al. (2020 ).…”

“…For complete details on the use and execution of this protocol, please refer to Zhao et al. (2020 ).…”