Leaf engineering puzzle better understood

Conserved cellular basis of plant growth are key to understanding leaf architecture

July 13, 2021
The Scitech

In a computational modeling and cell biology paper in the journal Nature Plants, Purdue’s Dan Szymanski, a professor in the Department of Botany and Plant Pathology, discovered that tensile force patterns in thin, pressurized cell walls carry information that pattern cell and tissue morphogenesis. The findings uncover a conserved cellular basis of plant growth and are key to understanding leaf architecture and potentially modifying it in the future to improve plants. “The leaf epidermis is like an exoskeleton, the growth of which determines the size and shape of organs,” Szymanski said. “We’re showing how groups of cells can function as dynamic building blocks for the organ. The tensile force patterns in the cell wall are decoded by a cytoskeleton-cell wall system that determines how cells in the tissue interact and grow at maximal rates. These cellular growth patterns can be maintained for days to affect tissue and organ-level morphology.”

Szymanski, in collaboration with Joseph Turner, a professor of mechanical and materials engineering at the University of Nebraska-Lincoln, showed that cells have areas of high tensile force in their walls. The magnitude and direction of these forces are sensed and mirrored by the microtubule cytoskeleton. The extracellular fibers accumulate and orient in these high-pressure areas to create patterns of cell expansion that maintain tissue integrity and enable the rapid expansion of thin-bladed leaves. A lobed morphology in internal cell types in the leaf enables efficient gas exchange for photosynthesis, and this cellular trait affects yield in major crop species. Szymanski’s group discovered a general mechanism for lobe formation in any plant cell type.

Realistic mechanical computational models of the cell wall showed that the microtubule system mirrors the magnitude and direction of wall tensile forces. Szymanski said. “We quantitatively showed that forces in the wall are sensed continuously by the microtubule system, he said. These microtubules, which were analyzed in real time by Samy Belteton, a graduate student in Szymanski’s lab, using live cell imaging, pattern the movement of cellulose synthase machines that make extracellular fibers that locally reinforce cell wall domains. This enables the tissue to grow adaptively in the expanding leaf. Szymanski and his collaborators identified the location and magnitude of the important tensile forces and the identity of the subset of microtubules controlling cell shape for the first time. This work provides important insights into how mechanical signaling at the cell periphery occurs and how it dictates local growth behaviors.

Source: Purdue University news release