This invention relates to sequences encoding .beta.-ketoacyl-ACP synthase (KAS) and methods of use thereof. Also provided are methods for decreasing saturated fatty acid levels as a component of total triglycerides found in plant oils. The method generally comprises growing a soybean plant having integrated into its genome a DNA construct comprising, in the 5' to 3' direction of transcription, a promoter functional in a soybean plant seed cell, a DNA sequence encoding a KAS protein, and a transcription termination region functional in a plant cell. The present invention also provides a soybean seed with less than about 3.5 weight percent total saturated fatty acids.