**Abstract**

Coconut palm (*Cocos nucifera* L) is an economically important monocot plant grown in tropical and subtropical regions. Coconut oil is stored in a solid endosperm and has 47.48–50.5% fatty acid component as lauric acid (C12:0). Present research showed that acyl-acyl carrier protein thioesterases (FatA/B) and lysophosphatidic acid acyltransferase (LAAPT) are key enzymes determining mediumchain fatty acid accumulation in coconut oil. Among five *CnFatB* genes, *CnFatB3* expressed specifically in endosperm and *in vitro* experiment showed that this gene made mainly lauric acid (C12:0) and tetradecenoic acid (C14:1). Overexpression of *CnFatB3* in *Arabidopsis* increased the amounts of C12:0 and C14:0 in transgenic plant. *CnLPAAT* gene that is expressed specifically in coconut endosperm showed a preference for using acyl-CoAs containing C10:0, C12:0, and C14:0 acyl groups as acyl-donor substrates. Coconut and oil palm are closely related species with approximately 50% lauric acid (C12:0) in their endosperm. The two species have a close evolutionary relationship between predominant gene isoforms and high conservation of gene expression bias in the lipid metabolism pathways. Moreover, since no stable transformation system has been constructed in coconut palm, gene function validations have been done in vitro, or genes transformed into a heterologous system.

**Keywords:** medium-chain fatty acid, lipid metabolism, coconut endosperm, gene evolution, de novo fatty acid synthesis, TAG biosynthesis
