Anthony Huang - US grants

Synthesis and degradation of triacylglycerols (TAG) in seeds during maturation and germination involve active metabolic pathways. Understanding the detailed mechanism of TAG metabolism will enable the control of food reserve deposition and utilization during active stages of the plant life cycle. It will also provide an indispensable information of how to breed or genetically engineer better seed oils for human utilization. The long term objective of the laboratory is to elucidate the mechanism of TAG metabolism in seeds. The focus is on a crucial TAG synthesizing enzyme, lysophosphatidate (LPA) acyltransferase, in maturing seed. This enzyme catalyzes the incorporation of acyl moiety from acyl CoA to the sn-2 position of 1-acyl-glycerol-3-phosphate, and the product phosphatidate will be further metabolized to either TAG or phospholipids. The enzyme has a very stringent acyl preference on both substrates, and thus controls the incorporation of preferred fatty acids into the sn-1 and sn-2 positions of TAG. The fatty acid composition, and thus the properties of seed TAG, rely heavily on the acyl preference of LPA acyltransferase. In this research proposal, the following two objectives will be pursued. The first objective is to examine whether seed LPA acyltransferase of a special acyl preference from one plant species will be active in another plant species after genetic transformation. Experiments will be performed to characterized seed LPA acyltransferases from palm, Brassica, and meadowfoam, to obtain their genes for transformation of appropriate plants, and to detect activities of the foreign enzymes in the transformed plants. Several different approaches will be used to obtain the gene; these approaches include: screening cDNA libraries for the genes by oligonucleotides deduced from the purified enzyme and by a bacterial gene, and functional complementation with a bacterial mutant. Putative E. coli mutant lines functionally complemented with plant cDNA encoding the enzyme have been obtained; these lines will be studied most intensively. If time permits, we will use the palm and meadowfoam LPA acyltransferase genes to transform Brassica, and analyze the transformed plants for activities of the foreign enzyme. The information will be crucial to our understanding of the control mechanism of fatty acid assembly into TAG in seeds as well as glycerolipids in non seed organs. The second objective is to test if a membrane-associated, lipid-metabolizing enzyme of bacterial origin can be active, in higher plants. by transforming Brassica with an E. coli gene encoding LPA acyltransferase and studying the expression of the bacterial gene in the transformed Brassica. %%% This project aims to take a gene which makes an enzyme that Produces a certain plant oil found in palms, and introduce the gene into other plants to see if they also would produce the palm oil. If this is successful the investigators have found a way for oil produced in plants not common to the US to be available in other species of plants common in this country. Furthermore, these enzymes could be used to make novel lipid biomaterials.

Sexual reproduction in plants is a dynamic process, and its mechanism and control are complicated. Research into the molecular basis of flowering and fruiting is intellectually intriguing as well as practical in agriculture. Promoting sexual reproduction could enhance the yield of fruits and seeds. Suppressing the process could increase the yield of vegetable produce. Other possible manipulations include utilizing male sterile genes to produce hybrid seeds, generating seedless fruits, and promoting self fertilization.

A major step in sexual reproduction is the interaction between the male sperm-containing pollen and the female egg-containing part in the flowers. This interaction is initiated largely by the molecules on the pollen surface. The pollen coat contains water-insoluble lipids and semi-water-soluble proteins as the major constituents. These lipids and proteins originate from subcellular particles in the parental cells enclosing the maturing pollen. The laboratory of Professor Anthony Huang at the University of California at Riverside will study these subcellular particles in Arabidopsis, a model plant of the cabbage family. The studies will emphasize the lipid and protein constituents in terms of their selective degradation and retention, their transport to and deposition on the pollen surface, and their function in the pollination and fertilization process. Arabidopsis mutants deficient in the lipids and proteins will be employed to dissect this parent-to-pollen pathway.

The results will delineate the mechanism of the control that the parental cells have over pollen maturation, especially on the pollen coat formation. They will also define the functions of the abundant lipids and proteins in the pollen coat in pollination, pollen germination, and tube penetration into the stigma.