The function and specificity of Golgi sugar nucleotide transporters in cell wall synthesis

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Plant cells are surrounded by rigid cell walls. Long chains made of a range of different types of sugars, known as polysaccharides, are major components of plant cell walls. Different plant cells and tissues vary in their properties largely due to differences in the wall polysaccharides. For example, as fruits ripen and soften, the polysaccharide pectin which functions as a glue holding cells together begins to be broken down. Cell walls polysaccharides are very important in our diet, as dietary fibre, and protect us against cancer and other diseases. By forming part of the barrier to attacking organisms, polysaccharides are also involved in plant resistance to diseases. However, we do not know the importance to the plant or to our diet of each particular polysaccharide component. If we could breed plants with different polysaccharide structures, we could investigate their importance to us and the plant. The Golgi apparatus is a structure that makes the polysaccharides within each cell. Individual sugar units are delivered to the enzymes making the long chain polysaccharides through the membrane of the Golgi apparatus. To do this, there are a large number of transporter proteins that take the sugars across the membrane. We have recently discovered four genes that direct the synthesis of four of these transporters, which we call GONSTs. We would like to study mutant plants missing each of these genes, to understand what the importance of each transporter is to the plant. We expect that these mutant plants will not be able to make all the normal polysaccharides, but we do not know precisely which polysaccharides will be affected. We also do not know what the consequences for the plant will be of having changed cell walls. Data we already have on one mutant tells us to expect that pectin synthesis will be affected. This will mean that the plant does not grow normally. When we have carried out this study, we will know how the structure of some of the wall polysaccharides can be changed in the laboratory. We should eventually be able to breed crop plants with changed polysaccharides in their wall, bringing dietary, industrial and agricultural benefits.