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

Abstract

Summary Lipid bodies are present in most plant cells and not just in storage tissues, such as seeds, as is often assumed. There is a growing number of proteins that are associated with lipid bodies in different plant tissues. In seeds, the most common class of lipid-body protein is the oleosins, which are found 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 problematic during dehydration but leads to a fatal coalescence of lipid bodies after germination. A class of anther-specific proteins has a precursor form that 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 are 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 and caleosin genes/proteins revealed an unexpected localisation in young root tips, as confirmed by expressing promoter-GUS constructs in transgenic plants. Several other classes of storage product-related genes hitherto believed to seed-specific are also transiently expressed in root tips following seed germination. We discuss the implications of these findings for root development and the use of «seed-specific» gene promoters in general.