Pectate lyases prune pectin to potentiate stomatal dynamics

Chen et al. uncover the effects of a pectate lyase-like gene on cell wall mechanics and cell pressurization in guard cells. The Plant Cell (2021) https://doi.org/10.1093/plcell/koab161

 By Yintong Chen and Charles T. Anderson

Department of Biology, The Pennsylvania State University, University Park, PA

Background: Stomata are tiny pores on the surfaces of plant leaves. Stomatal opening and closure control gas exchange between the plant and the atmosphere and are controlled by the swelling and shrinking of guard cells that flank the stomatal pore. Scientists are combining cell biology, genetics, mechanical measurements, and computer modeling to study how guard cells deform. Plant cell walls are important for guard cell deformation because they must be strong and flexible to enable their reversible growth and shrinkage. Guard cell walls contain cellulose that wraps around the cell and other polysaccharides including hemicelluloses and pectins. Changing how the cell wall is built and modified can influence the development and function of stomatal guard cells.

Question: We do not fully understand how the construction and modification of complex cell walls allow stomata to function. Here, we asked how pectin degradation in the guard cell wall by enzymes called pectate lyases affects wall structure and stomatal dynamics. We also investigated the mechanical forces that drive guard cell swelling and shrinking.

Findings: We found that a pectate lyase-like gene, PLL12 (PECTATE LYASE LIKE12), contributes to stomatal development and dynamics in Arabidopsis thaliana. To probe the forces underlying stomatal dynamics, we measured the force required to make tiny indentations in guard cells as stomata opened and closed and used computational modeling to dissect cell wall stiffness from guard cell pressure. We noticed surprising changes during stomatal opening in both values, which were abnormal in plants lacking PLL12. Fluorescent labeling and microscopy revealed that cell wall structure was abnormal in guard cells lacking PLL12. Finally, we found that knocking out or diminishing PLL12 function causes smaller leaves, hinting at a connection between stomatal function and leaf growth.

Next steps: We are studying how the changes in pressure and wall stiffness that occur as stomata open and close are accomplished. We are using high-resolution microscopy and molecular modeling of guard cell walls to help answer this question. We are also examining whether mechano-sensors in guard cells or signaling by pectin fragments might affect stomatal function.

Yintong Chen, Wenlong Li, Joseph A. Turner, Charles T. Anderson (2021). PECTATE LYASE LIKE12 patterns the guard cell wall to coordinate turgor pressure and wall mechanics for proper stomatal function in Arabidopsis. https://doi.org/10.1093/plcell/koab161