Genome-wide analysis of oleosin gene family in 22 tree species: An accelerator for metabolic engineering of biofuel crops and agrigenomics industrial applications?

Authors: Cao, Heping

Submitted to: Omics - A Journal Of Integrative Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2015
Publication Date: 9/8/2015
Citation: Cao, H. 2015. Genome-wide analysis of oleosin gene family in 22 tree species: An accelerator for metabolic engineering of biofuel crops and agrigenomics industrial applications? Omics - A Journal Of Integrative Biology. 19(9):521-541.

Interpretive Summary: Triacylglycerols (TAGs) are the major molecules of energy storage in eukaryotes. Trees contribute to part of enormous plant oil reserves because fruits and kernels of many trees contain up to 50-80% of oil. TAGs accumulate in oil bodies in plants, similar to oil droplets in animals. Oleosins (OLEs) are a group of mostly low-molecular-mass hydrophobic proteins localized on the surfaces of plant oil bodies. OLEs/oils ratio determines the size and shape of intracellular oil bodies. However, there is a lack of comprehensive sequence analysis of OLEs among diverse trees. This study identified OLEs from tree species, performed genome-wide analysis of tree OLEs, classified tree OLEs, identified conserved sequence motifs and amino acid residues in tree OLEs and OLE subfamilies, and confirmed their expression in tung tree seeds. Data mining identified 65 OLEs with perfect conservation of the “proline knot” motif (PX5SPX3P) from 19 tree species. These OLEs had similar properties and amino acid composition with > 40% hydrophobic amino acid residues. Genome-wide phylogenetic analysis and multiple sequence alignment separated these proteins into 5 OLE subfamilies. There were distinct patterns of sequence conservation among the OLE subfamilies and within individual species. This systematic analysis of OLE sequences led to identify incomplete OLE sequences, repetitive entries in the database, and divergent sequences from the completely conserved motif. These analyses should also facilitate studying the structure-function relationship and identify critical amino acid residues in OLEs for metabolic engineering of tree TAGs.

Technical Abstract: Triacylglycerols (TAGs) are the major molecules of energy storage in eukaryotes. Trees contribute to part of enormous plant oil reserves because fruits and kernels of many trees contain up to 50-80% of oil. TAGs accumulate in oil bodies in plants, similar to oil droplets in animals. Oleosins (OLEs) are a group of mostly low-molecular-mass hydrophobic proteins localized on the surfaces of plant oil bodies. OLEs/oils ratio determines the size and shape of intracellular oil bodies. However, there is a lack of comprehensive sequence analysis of OLEs among diverse trees. The objectives of this study were to identify OLEs from tree species, to perform genome-wide analysis of tree OLEs, to classify tree OLEs, and to identify conserved sequence motifs and amino acid residues in tree OLEs and OLE subfamilies. Data mining identified 65 OLEs with perfect conservation of the “proline knot” motif (PX5SPX3P) from 19 trees including 5 sequenced tree genomes of Prunus persica (peach), Populus trichocarpa (poplar), Ricinus communis (castor bean), Theobroma cacao (cacao) and Vitis vinifera (grapevine). These OLEs were hydrophobic proteins with > 40% hydrophobic amino acid residues. They had similar properties and amino acid composition. Genome-wide phylogenetic analysis and multiple sequence alignment demonstrated that these proteins were separated into 5 OLE subfamilies. There were distinct patterns of sequence conservation among the OLE subfamilies and within individual species. As an example, expression of the five subfamilies of OLE from tung tree was demonstrated by quantitative real-time PCR. These analyses should facilitate studying the structure-function relationship and identify critical amino acid residues in OLEs for metabolic engineering of tree TAGs.