Anthony H. C. Huang
Professor of Plant Cell Biology
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Professor of Plant Cell and Molecular Biology Phone: (951) 827-4783 EMAIL: anthony.huang@ucr.edu |
- 1969 B.S. (Botany), National Taiwan University, Taiwan
- 1973 Ph.D. (Biology), University of California, Santa Cruz
- 12/72 - 8/73 Postdoctoral, Biology Dept., Univ. of California, Santa Cruz
- 9/73 - 5/88 Asst., Assoc., and full Prof., Biol. Dept., U. South Carolina, Columbia
- 8/87 - 5/88 Carolina Research Professor, Univ. of S. Carolina, Columbia
- 5/88 - Professor, Dept. of Botany & Plant Sciences, Univ. of Calif., Riverside
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
Huang AHC (2004) Endoplasmic reticulum and oleosins in seed and tapetum. Plant Physiol. (in press).
Ting JTL, Balsamo RA, Ratnayake C, Huang AHC (1997) Oleosin of plant seed oil bodies is correctly targeted to the lipid bodies in transformed yeast. J Biol Chem 272: 3699-3706.
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:
Publications Related to Cell/Molecular/Developmental Biology of Flowers, with emphases on the tapetum cells in the anthers
Suen DF, Wu SSH, Chang HC, KS Dhugga, Huang AHC (2003) Cell wall reactive proteins in the coat and wall of maize pollen. Potential role in pollen tube growth on the stigma and through the style. J Biol Chem 278: 43672-43681.
Wu SSH, Suen DF, Chang HC, Huang AHC (2002) Maize tapetum xylanase is synthesized as a precursor, processed and activated by a serine protease, and deposited on the pollen. J Biol Chem 277: 49055-49064.
Kim HU, Hsieh K, Ratnayake C, Huang AHC (2002) Expression of Arabidopsis oleosin genes and characterization of their encoded oleosins. J Biol Chem 277:22677-22684.
Kim HU, Wu SSH, Ratnayake C, Huang AHC (2001) Brassica rapa has three genes that encode proteins associated with different neutral lipids in plastids of specific tissues. Plant Physiol 126:330-341.
Bih FY, Wu SSH, Ratnayake C, Walling LL, Nothnagel EA, Huang AHC (1999) The predominant protein on the surface of maize pollen is an endo-xylanase synthesized by a tapetum mRNA with a long 5' leader. J Biol Chem 274: 22884-22894.
Ting JTL, Wu SSH, Ratnayake C, Huang AHC (1998) Constituents of the tapetosomes and elaioplasts in Brassica campestris and their degradation and retention during microsporogenesis. Plant J 16: 541-551.
Wu SSH, Platt KA, Ratnayake C, Wang TW, Ting JTL, Huang AHC (1997) Isolation and characterization of novel neutral-lipid-containing organelles and globuli-filled plastids from Brassica napus tapetum. Proc. Natl. Acad. Sci USA 94:12711-12716.
Wang TW, Balsamo RA, Ratnayake C, Platt KA, Ting JTL, Huang AHC (1997) Identification, subcellular localization, and developmental studies of oleosins in the anther of Brassica napus. Plant J. 11:475-487.
Fig. 1 (below) - 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 (below) - 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.
