Evidence of a Transition from Diffusive to Super-Diffusive Motion of Cellulose Synthase Complexes in Living Plants

Abstract

The polysaccharide cellulose is the main component of plant cell walls, so it is the most abundant polymer on the earth. While it is widely used in industry due to its remarkable properties, such as renewability and biodegradability, its biosynthesis is still not well understood. The large transmembrane protein complex responsible for synthesizing cellulose contains several cellulose synthase A (CESA) subunits that polymerize UDP glucose into the constituent glucan chains of cellulose. Here, we used variable angle epi-fluorescence microscopy in combination with single-particle tracking to characterize the motion of GFP labeled CESA complexes in the root and mesocotyl of Brachypodium distachyon seedlings that are a 3 to 4 days old. We show that CESA complexes move through the plasma membrane at approximately 165 nm/minute. Their motion is known to be guided by cortical microtubules, but no molecular motors are involved. Rather, the motion is thought to be driven by the polymerization and crystallization of the cellulose. A mean-squared displacement analysis shows that CESA complexes move diffusively on short time scales and undergo a transition to super-diffusive motion on a time scale of about 10 s. We also report on the effect of actin and microtubule inhibitors on CESA motion.