Christoph Benning (Institute fur Genbiologische Forschung, Berlin) described progress toward understanding the biosynthesis and function of specific lipids. By screening several thousand lipid extracts from a mutagenized population by TLC chromatography, his laboratory identified a mutant that is deficient in the chloroplast-specific lipid digalactosyldiacylglycerol (DGD). Surprisingly, this mutant is viable but shows various alterations in the organization of chloroplast membranes. Also surprising was the observation that the mutant appears to have normal activity for all of the enzymes proposed to be involved in DGD synthesis. The mutant has, therefore, provided an impetus for the formulation of a new pathway for the synthesis of DGD and possibly other chloroplast lipids. He also described progress towards identifying genes involved in the synthesis of sulfolipid. This lipid is one of the most abundant sulfur-containing organic molecules but only one step in the pathway of synthesis is known. Members of his lab have cloned many of the genes for sulfolipid synthesis from a purple bacterium and a cyanobacterium. They have used sequence information from these genes to identify a homologous sequence in a rice EST. This will facilitate a test of the role of sulfolipid by the production of transgenic Arabidopsis plants expressing an antisense version of the corresponding Arabidopsis gene.
Bertrand Lemieux (York University, Toronto) described progress in the isolation of genes controlling the synthesis and deposition of epicuticular wax. In collaboration with Ken Feldman, at least five cer genes have been tagged with TDNA. The genes for two of these, cer2 and cer3 have been isolated and characterized. Both genes encode novel proteins of unknown function. Thus, although it seems likely that these genes encode enzymes involved in wax biosynthesis additional work will be required to assign function.
Chistiane Nawrath (University of Fribourg, Fribourg) summarized experiments concerning the production of biodegradable thermoplastics in plants. The polymer, polyhydroxybutyrate (PHB), is synthesized in three steps from acetyl-CoA. High levels of production of PHB in transgenic plants was obtained by restructuring three genes from the bacterium Alcaligenes eutrophus so that the gene products were imported into chloroplasts. Trihybrid plants containing all three genes accumulated more than 14% of the dry weight as granules of PHB without exhibiting any obviously deleterious effects on growth. On the basis of these experiments it appears likely that PHB and related polymers can be produced at economically feasible levels in agricultural species.
Tod Richmond (University of Wisconsin, Madison) gave a short talk describing a pleiotropic T-DNA mutation that causes aberrant floral morphology and sterility among other things. Oddly, the mutation appears to inactive a tetrafunctional protein involved in beta-oxidation of fatty acids. There is no apparent explanation as to how beta-oxidation and morphogenesis could be causally related.
Jyan-chyun Jang (Massachusetts General Hospital, Boston) presented a short talk describing the isolation of mutants that are either hypersensitive or insensitive to exogenous sugars and summarized evidence from antisense experiments showing that hexokinase is involved in the phenomenon of sugar sensing.