Role of lipid bodies and lipid-body proteins in seeds and other tissues

Lipid bodies are present in most plant cells and not just in storage tissue s, such as seeds, as is often assumed. There is a growing number of protein s that are associated with lipid bodies in different plant tissues. In seed s, the most common class of lipid-body protein is the oleosins, which are f ound on the surfaces on lipid bodies in all desiccation tolerant plants but are absent from lipid bodies in the seeds of desiccation-sensitive plants, e.g. cocoa or neem. The absence of oleosins in these seeds is not. problem atic during dehydration but leads to a fatal coalescence of lipid bodies af ter germination, A class of anther-specific proteins has a precursor form t hat contains an oleosin-like hydrophobic domain and is initially localised on lipid bodies in the tapetum. However, the oleosin-like domain is cleaved off after release into the anther locule and the mature proteins, which ar e the major protein components of the pollen coat, contain no oleosin-like sequences. Therefore these proteins, which have been named "pollenins", use their oleosin-like domain as a novel form of cleavable targeting sequence. A third type of lipid-body protein is caleosin, which also has endoplasmic reticulum associated isoforms and may be involved in lipid-body biogenesis and membrane trafficking. Analysis of the expression patterns of oleosin a nd caleosin genes/proteins revealed an unexpected localisation in young roo t tips, as confirmed by expressing promoter-GUS constructs in transgenic pl ants. Several other classes of storage product-related genes hitherto belie ved to seed-specific are also transiently expressed in root tips following seed germination, We discuss the implications of these findings for root de velopment and the use of "seed-specific" gene promoters in general.