Although no common sequence motif between sorting signals has been found, we have shown that they are interchangeable. We have isolated a few components of the vesicle transport machinery, and are now studying their precise function in plants. Plant vacuolar targeting signals. Schematic diagram of the types of targeting signals within vacuolar proteins. Some components may be common to all vesicle transport systems, but others could be plant-specific.
Plant cells appear to contain more than one kind of vacuolar compartment.
It is not known whether all proteins are transported to the vacuole in the same type of vesicle or different vesicle classes function in the transport of various proteins. Another aspect of vacuolar transport that is now being studied in plants is the differential regulation of transport processes and machineries between various tissues and cell types. There appears to be a difference in the expression level of some components of the sorting machinery between tissues, which may reflect functional variations in divergent tissues and their constituent cell types. Mechanistic differences between cell types have also been observed, as certain proteins that are vacuolar in leaves are found extracellularly in roots. The availability of marker proteins in the various organelles of the plant endomembrane system will now allow many of these issues to be addressed.