Microtubule Associated Proteins affect stomatal aperture size

Climate change threatens the productivity of our agricultural plants. Increased heat and drought conditions challenge plants and reduce crop yield. Stomata are epidermal structures on the surface of plant leaves that mediate multiple physiological processes including photosynthesis, thermoregulation and water homeostasis. Hundreds of stomata are found on each leaf, and each stoma is composed of two identical guard cells that surround a central aperture. Guard cells regulate the flow of gases from inside the leaf to the atmosphere through the aperture. The current paradigm is that water pressure within the guard cells determine the size of the aperture and thereby adjust gas exchange to maintain physiological homeostasis. Recent data show a correlation between microtubule organization within the guard cells and aperture size. To further understand the role of microtubules in stomata, we studied the model flowering plant Arabidopsis thaliana harboring genetic mutations in two microtubule associated proteins, KATANIN and ZWICHEL. Cellular observations of wild type stomatal apertures show smaller apertures in the dark than in light, due to the increased photosynthetic activity during the day light. However, stomatal apertures in the katanin and zwichel mutants differed from wildtype and from each other in both the dark and light growth periods. Both KATANIN and ZWICHEL proteins are known to be important for organizing the interphase cortical array of microtubules in Arabidopsis. Therefore our data suggest that microtubule organization is needed for regulating aperture size.