Fatty acid synthesis: from CO2 to functional genomics

Area of Science:

• Plant biochemistry and molecular biology
• Metabolic pathway analysis
• Gene expression profiling

Background:

• Uncertainty exists regarding the pathway of CO2 to acetyl-CoA in chloroplasts for fatty acid synthesis.
• Free acetate is an effective substrate for isolated chloroplasts, but its in-vivo generation mechanism is unclear.
• A direct pathway from pyruvate via plastid pyruvate dehydrogenase is a plausible alternative.

Purpose of the Study:

• To elucidate the in-vivo pathway of CO2 to acetyl-CoA in plant leaves.
• To investigate the regulation of plant lipid metabolism, particularly in developing oilseeds.
• To identify tissue-specific gene expression patterns in Arabidopsis.

Main Methods:

• Kinetics of (13)CO2 and (14)CO2 incorporation into fatty acids in leaves under light and dark conditions.
• Development and application of custom microarrays for analyzing approximately 5000 seed-expressed Arabidopsis genes.
• Hybridization of microarrays with probes from seeds, leaves, and roots to determine tissue-specific gene expression.

Main Results:

• Rapid incorporation of (14)C into fatty acids (< 2-3 min) suggests free acetate is not a major intermediate in leaf fatty acid synthesis.
• An estimated turnover rate for fatty acids in leaves was determined.
• Approximately 10% of analyzed genes showed >10-fold higher expression in seeds compared to leaves or roots, including potential regulatory factors and proteins of unknown function.
• Microarrays proved useful for analyzing Brassica seed gene expression.

Conclusions:

• The study provides evidence against a significant role for free acetate as an intermediate in leaf fatty acid synthesis.
• Developed microarrays offer a powerful tool for global gene expression analysis in developing oilseeds and understanding regulatory networks.
• Tissue-specific gene expression patterns reveal novel insights into seed development and lipid metabolism.