The oleosin gene family in coffee: Analysis of oleosomes, oleosins and lipid-related gene expression during germination of Coffea arabica seeds

Abstract

Little information is available about lipid metabolism in Coffea arabica L. seeds, which have an oil content between 11 and 16% w/w. This is surprising given the involvement of lipids in the physical, chemical, and physiological properties of the coffee beverage. To shed light on this subject, freshly harvested C. arabica seeds were sampled at different stages of germination. Oleosomes (the organelles responsible for lipid storage) were extracted and their structure was observed by differential interference-contrast microscopy. Triacylglycerol content of oleosomes was analyzed by thin-layer chromatography, and the protein fraction was evaluated by gel electrophoresis. A review of available genomic data on oleosin and lipase genes was performed, and expression of genes related to lipid metabolism was measured by Real-Time PCR.The results drew a coherent picture of coffee seed germination, revealing that oleosins have the highest concentration after 14 days of germination, followed by a marked decrease. This was backed up by molecular observations, showing how oleosin genes were downregulated after 6–9 days of germination, while genes related to lipid degradation were upregulated from day 9 onwards. Morphological evidence supported these findings, as after 14 days embryo growth became significant and cotyledons started to invade the endosperm and metabolize seed reserves. The present research will be an important first step in better understanding the biology of oleosomes in Coffea arabica L. and in elucidating the role of lipid metabolism in green coffee quality.