Abstract
From smooth to buckled, nature exhibits organs of various shapes and forms. How cellular growth patterns produce smooth organ shapes such as leaves and sepals remains unclear. Here we show that unidirectional growth and comparable stiffness across both epidermal layers of Arabidopsis sepals are essential for smoothness. We identified a mutant with ectopic ASYMMETRIC LEAVES 2 (AS2) expression on the outer epidermis. Our analysis reveals that ectopic AS2 expression causes outer epidermal buckling at early stages of sepal development, due to conflicting growth directions and unequal epidermal stiffnesses. Aligning growth direction and increasing stiffness of the outer epidermis restores smoothness. Furthermore, buckling influences auxin efflux transporter protein PIN-FORMED 1 polarity to generate outgrowth in the later stages, suggesting that buckling is sufficient to initiate outgrowths. Our findings suggest that in addition to molecular cues influencing tissue mechanics, tissue mechanics can also modulate molecular signals, giving rise to well-defined shapes.
One-Sentence Summary The asymmetric leaves 2-7D mutant sepals buckle due to discoordination of growth between the two epidermal layers.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
The revised version now contains the following:- 1) Changes in the main text to improve clarity, and moving some supplementary figures to the main figures. 2) Inclusion of numerical simulations for the analytical model. 3) Exploration of parameter space for the numerical simulations, provided as supplementary figures. 4) Analysis of the growth parameters of the outermost mesophyll cell layer of the WT and as2-7D sepals, provided as a supplementary figure. 5) Phenotypic characterization of kan1kan2 double mutants provided as a supplementary figure. 6) Live imaging of pPIN1::PIN1-GFP as2-7D sepals from initial stages prior to buckling, through the stages where the outer epidermis buckles and outgrowths are evident, provided as a supplementary figure.
https://github.com/Avilash1993/R_codes_for_plots_as2-7D_sepal_buckling