Protein tubes bring enzymes to the starting line

The enzymes that create cellulose in plants are transported to their ‘workplace’ through a network of protein tubes and threads. This was shown by researchers Professor Anne Mie Emons and PhD student Jelmer Lindeboom of the Laboratory of Plant Cell Biology of Wageningen University, along with their colleagues from Stanford University (USA). The findings were published in Nature Cell Biology.

The production of cellulose in plants is very important. This polymer provides solidity to the cell walls and thereby primarily defines the shape of the plant. The production of microcrystalline cellulose fibres, also called microfibrils, is not a random process, but a very precise one, which depends on the type of cell and its requirements. ‘You could compare to reinforced concrete. If you don’t place the reinforcement in just the right place, you won’t end up with the proper strength and shape’, states Emons.

According to Emmons, it was already known that these enzyme complexes – which produce cellulose in plants – move through the cell membrane, guided by the microtubules. These protein tubes, part of the cytoskeleton, are located inside the cell membrane. Enzyme complexes follow these ‘rails’ while they spin cellulose microfibrils, similar to a snail leaving behind a trail of slime.

The researchers from Stanford University made that discovery in 2006 by using fluorescent proteins. This made it possible to glimpse the cellulose-producing enzymes and the microtubules while they were active. The same technique was also used for this new research, which was published online in Nature Cell Biology on 14 June. This time it was used to discover where the enzyme complexes begin their work. ‘It appears that the locations where they are placed within the cell membrane are also determined by the microtubules. They work like a kind of customs office, making sure the enzymes are admitted to the right locations,’ explains Emons.

In addition, research has shown that the supply of the enzymes in the direction of the cell wall is directed by another part of the cytoskeleton: the actin filaments that run through the cell. The protein threads escort the bodies that initially contain the enzymes towards the cell membrane, where the microtubules take on the precision work.

‘This is fundamental research that is very important to our perception of the plant itself, but over the longer term such knowledge could also enable us to create plants that are better suited for specific purposes, such as paper manufacturing, food or biofuel’, says Emons. ‘For all these purposes, fundamental knowledge is required about the biosynthesis of cellulose. No applications are possible without fundamental knowledge.’ / RN