Cellulose microfibrils, the major tensile components of the plant cell wall, play an essential role in plant growth and development. In higher plants, cellulose is synthesized at the plasma membrane (PM) by large cellulose synthase complexes (CSC) consisting of multiple cellulose synthase (CESA) proteins. Cellulose production is influenced by the rate of intracellular trafficking of CSCs and their lifetime at the PM. CSCs are believed to be assembled in the Golgi apparatus and delivered to the PM via small microtubule-associated transport vesicles, and their uptake into the cytosol is mediated by clathrin-based endocytic machinery. Both processes are likely to involve the actin cytoskeleton serving as tracks for vesicle or organelle transport, as well as clathrin-coated vesicle formation. Myosins XI are motor proteins that move diverse organelles and vesicles along actin filaments, thus playing a critical role in organelle trafficking in plant cells. However, the molecular mechanisms by which actin and myosin contribute to CSC trafficking or cellulose deposition remain obscure. In this study, measurements of cellulose content demonstrate that cellulose biosynthesis is significantly reduced in a myosin xik xi1 xi2 triple knockout (3KO) mutant. By quantitative image analysis of living epidermal cells expressing a functional YFP-CESA6 reporter in both the xi3KO mutant and myosin inhibitor-treated cells, we show that myosin regulates the abundance of PM-localized CSCs and determines the rate of delivery of CSCs to the PM by mediating the transport and exocytosis of small CESA-containing compartments. These are the first data implicating myosin in cellulose production in higher plants.

Myosins XI are involved in cellulose synthase complex dynamics and delivery

253rd National Meeting (2017)

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