Arabidopsis myosin is involved in the distribution and dynamic behavior of the cellulose synthase complex
Plant cells are encased in cell walls which are important for the growth and development of the organism. Primary cell wall consists mainly of polysaccharides with cellulose as the most abundant component. In plant cells, cellulose is synthesized by a plasma membrane (PM) localized protein complex called the cellulose synthase complex (CSC). It was previously reported that disrupting normal actin organization resulted in a reduction of cellulose content in Arabidopsis dark-grown seedlings. Furthermore, actin was found to facilitate the delivery of CSC into the PM, and inferred to be involved in endocytosis. As a motor protein that translocates cargo along actin filaments, myosin plays an important role in organelle and vesicle trafficking. However, it is not known whether myosin is involved in regulating cellulose deposition or CSC behavior. Here, we used biochemical analysis to determine the cellulose content in Arabidopsis etiolated seedlings, and found a significantly decreased cellulose content in a myosin xi-1, xi-2, and xi-k triple knockout mutant (xi3KO), indicating that myosin is involved in cellulose deposition. To evaluate the molecular mechanism underlying the role of myosin in CSC trafficking, we characterized and employed a new plant myosin inhibitor, pentabromopseudilin (PBP), which was previously used to inhibit the function of animal and yeast myosins V. With this pharmacological tool, we discovered that treatments with myosin inhibitors reduced the density of CSC at the PM, as well as the rate of delivery of CSC to the PM, which is used to infer that plant myosin is involved in the delivery and internalization of CSC at the PM. Surprisingly, we found that the motility of CSC was significantly inhibited upon treatment with myosin inhibitors, which is different from the results with the actin-polymerization inhibitor Latrunculin B (LatB). Moreover, myosin inhibitor-treated cells showed an altered microtubule orientation, whereas LatB treatment had no effect. These results provide the first evidence that myosin is involved in cellulose deposition and offer insights for the potential mechanism of how myosin regulates CSC behavior.^
Christopher J. Staiger, Purdue University.
Biology|Cellular biology|Plant sciences