UC Riverside

Eukaryotes and prokaryotes contain neutral lipids in subcellular droplets as food reserves and/or for other purposes. Among all of the lipid droplets in diverse organisms, those in plant seeds are the most prominent. Lipid droplets in higher plants are present in seeds, pollens, fruits and flowers. Lipids from plants are important for human and farm-animal nutrition as well as industrial uses. Plant storage lipid droplets are stabilized with abundant structural proteins called oleosins, which contain a long conserved central hydrophobic hairpin structure penetrating into the matrix of the droplet. Plant lipid droplets with oleosins covering the surface are also termed oil bodies. The expression of oleosin genes is regulated individually in a tissue-specific manner in coordination with the biogenesis of oil bodies. This dissertation aims at delineating the evolution and functions of oleosins and oil bodies in primitive and advanced plant species. I have found that the primitive plant moss, Physcomitrella patens, possesses 3 oleosin genes. I have delineated the early evolution of these oleosin genes and the storage functions of the oleosin- enclosed oil bodies. In addition to seeds, tapeta of Brassicaceae also contain numerous oleosin-coated oil bodies, which are associated with flavonoid-containing vesicles to form abundant tapetosomes. Species in Brassicaceae possess a cluster of 4-7 oleosin genes specifically expressed in tapeta. I have established quantitative adaptive benefit of the oleosin gene cluster members conferring dehydration-tolerant pollen. I have found that Cleomaceae, the family closest to Brassicacea, does not possess the oleosin gene cluster or tapetosomes. Transformation of Cleomecacea with an Arabidopsis oleosin gene generates primitive tapetosomes and dehydration-tolerant pollen.