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CEPCEB Members
1969
B.S. (Botany), National Taiwan University, Taiwan Two related research projects are being pursued: Cell/Molecular/Developmental Biology of Oils and Proteins in Seeds Seeds store food reserves that will be mobilized to support germination and seedling growth. These reserves include proteins, oils, and carbohydrates, and are used by human for food and non-food purposes. We have been studying the mechanism whereby these food reserves, especially the oils and proteins, are synthesized and degraded during seed maturation and germination. One objective is to manipulate the quality and quantity of seed oils and proteins via genetic engineering. There are 4-5 enzymes for the
conversion of glycerol-3-phosphate to triacylglycerols in maturing seeds. We have
been characterizing these enzymes and their genes to understand their roles in
regulating the quality and quantity of the triacylglycerols synthesized. These
enzymes are present in the endoplasmic reticulum, and the product triacylglycerols
are channeled to subcellular storage oil bodies. The spherical oil body has a
diameter of ~ 0.6-2.0 ?m. It has a matrix of triacylglycerols enclosed by a layer
of phospholipids and structural proteins called oleosins (Figure 1). An oleosin
molecule has a highly conserved, long hydrophobic stretch of 72 amino acid residues,
which form a hairpin penetrating into the matrix of the oil body. Oleosins are
abundant proteins in the mature seeds, and in Brassica, they represent 10% of
the total seed proteins. We have been characterizing the oleosins and their genes,
as well as the cell biology of the oil bodies. We also study the seed storage
proteins and their storage house, the protein bodies. Recent publications include:
Selected Publications Related to Cell/Molecular/Developmental
Biology of Oils and Proteins in Seeds
Cell/Molecular/Developmental Biology of Flowers with Emphases on the Tapetum Cells in the Anthers Sexual reproduction in plants is a dynamic process. Research into the molecular basis of floral initiation, flowering and fruiting is highly applicable in the manipulation of sexual reproduction in crops for enhancing production. A major step in sexual reproduction is the interaction between the male-gamete-containing pollen and the female stigma in the flowers. The interaction is initiated largely by the constituents in the pollen coat. These constituents are synthesized in the tapetum cells enclosing the locule and are discharged onto the maturing pollen surface. In wind-pollinating species such as maize, the pollen coat contains cell wall hydrolytic enzymes, which aid the penetration of the pollen tube through the stigma into the style. In insect/self-pollinating species such as Brassica and Arabidopsis, the pollen coat contains neutral lipids (steryl esters and others) and amphipathic proteins (oleosins) for waterproofing and water uptake, respectively. These lipids and proteins are initially accumulated in two abundant organelles in the tapetum cells. One of these organelles is the plastid, which temporarily houses the steryl esters. The other organelle is the tapetosome, which possesses triacylglycerols and oleosins; only specifically fragmented oleosins will be deposited onto the pollen surface (Figure 2). The tapetosomes have unique morphology
and constituents. They contain triacylglycerol droplets situated among densely
packed vesicles and do not have an enclosing membrane. They contain oleosins,
which presumably are associated with the triacylglycerol droplets. The synthesis
of the tapetosomes is intimately related to the rough ER. We have been studying
the biogenesis of the tapetosomes on the basis of the following working hypothesis.
Initially, lipid droplets alone or in clusters are produced in the cytoplasm,
possibly by a special budding process from the ER, analogous to the formation
of a seed oil body. These lipid droplets are adjacent to, or directly associated
with, the ER. The clustered lipid droplets become a primitive tapetosome, which
is associated with massive ER. Subsequently, the smooth ER near the cluster is
detached to become vesicles/lamella inside the tapetosome. Membranes do not enclose
the organelle, although some of the tubular/lamellar ER may be on the organelle
surface. At the late stage of anther development before/during/after the tapetum
cell lyzes, the tapetosomes undergo selective degradation, and the retained constituents
are deposited onto the pollen surface. All the triacylglycerols are completely
degraded, whereas the oleosins are selectively fragmented. We have been studying
the degradation of the tapetosomes and exploring the mechanism of programmed cell
death of the tapetum cells. Recent references include:
Selected Publications Related to Cell/Molecular/Development Biology of Flowers (Bibliography page)
Fig. 1. In the model of a seed oil body, the oil (blue), the phospholipids (red), and oleosin (yellowish green) are shown in proportional sizes. The size of the oil body relative to the molecules is diminished to reveal the surface structure.
Fig. 2. A model of the transfer of oleosin of the tapetosome and steryl esters of the elaioplast from a tapetum cell to the surface of a maturing pollen. Triglycerides of the tapetosome and the structural protein of the elaioplast are not transferred but are degraded. On the pollen surface, oleosin and steryl esters are for water uptake and waterproofing, respectively. | ||||||||||||||
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