Cloning, molecular analysis, and developmental expression of 3 oleosin cDNA isoforms in coconut (Cocos nucifera L.)

Coconut stores its lipid reserves in the endosperm, specifically in oil bodies that contain proteins called oleosins which stabilise their structure. This study reports the complete cDNA sequences of 3 genes for 3 isoforms of oleosin termed CnOLE500a, CnOLE500c, and CnOLE300a with 396, 375, and 381 nucleotides, respectively. Their predicted amino acid sequences were 131, 124, and 126 residues in length, respectively, with molecular weights of 13,787, 12,982, and 12,988Da, respectively. The complete CnOLE500a cDNA sequence had 83.1% similarity with that of CnOLE500c, while CnOLE300a cDNA had only 50.7% and 46.5% similarity with CnOLE500a and CnOLE500c, respectively. None of the 3 coconut oleosins had the 18 amino acid insertion characteristics of H-class oleosins, thus they belonged to the L-class of oleosins. However, phylogenetic analysis showed that CnOLE300a was more related to H-class oleosins from dicots. All 3 isoforms were highly expressed at all stages of coconut endosperm development. CnOLE500c exhibited 6% higher expression than CnOLE500a and 15% higher than CnOLE300a at all stages of coconut endosperm development. However, oleosin proteins were barely detectable in the solid endosperm of coconut at 5-6months, but this increased 20-fold at 6-7months, and increased by a further 2- and 12-fold, at 7-8 and 8-9months, respectively.