Trafficking of Xylan to Plant Cell Walls

Plant cell walls are classified as primary and secondary walls. The primary wall is necessary for plant morphogenesis and supports cell growth and expansion. Once the growth and expansion ceases, specialized cells form secondary walls in order to give strength and rigidity to the plant. Secondary cell walls are the main constituent of woody biomass. This biomass is raw material for industrial products, food, and biomaterials. Recently, there are an increasing number of studies using biomass for biofuel production and this area has gained importance. However, there are still many unknowns regarding the synthesis and structure of complex polysaccharides forming biomass. Cellulose, being one of the main components of the cell wall, is synthesized at the plasma membrane by cellulose synthase complexes and does not require transportation. On the other hand, pectin and hemicelluloses are synthesized by enzymes located in the Golgi apparatus. Therefore, they need to be transported to the plasma membrane. Even though this transport mechanism is very important, it is one of the least understood parts of the endomembrane system. Xylan is the major hemicellulose in many biomasses and is important for renewable material production. There is limited knowledge about the cellular trafficking of xylan. In this review, we cover the current information and what we know about the vesicular transport of xylan to the cell wall.