Differential expression of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) during flower and fruit development of Bixa orellana

Annatto (Bixa orellana, family Bixaceae) is a tropical plant of great agroindustrial interest because of the high content of bixin, a carotenoid pigment produced in seeds and which is widely used in the food industry. This work takes a biochemical and molecular approach to flower and fruit development of this plant. The enzyme activity and genetic expression of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR), which play an important role in the synthesis of isopentenyl pyrophosphate, the precursor of isoprenoids, were investigated during flowering, fruit development and seed formation. A fragment of 503 bp of the hmg gene derived from genomic DNA was obtained using the polymerase chain reaction (PCR) and used as a probe to analyze the hmg gene copy number and expression pattern. Southern blot analysis suggested that hmg is encoded by a multigene family. Among the different plant tissues, the highest specific enzyme activity was observed in seeds, particularly at the immature stage when it was 3.6-fold higher than in the mature seed. These data correlated with those of transcript accumulation, suggesting HMGR activity during seed development is under transcriptional control.