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 agroi ndustrial interest because of the high content of bixin, a carotenoid pigme nt produced in seeds and which is widely used in the food industry. This wo rk takes a biochemical and molecular approach to flower and fruit developme nt of this plant. The enzyme activity and genetic expression of 3-hydroxy-3 -methylglutaryl CoA reductase (HMGR), which play an important role in the s ynthesis of isopentenyl pyrophosphate, the precursor of isoprenoids, were i nvestigated during flowering, fruit development and seed formation. A fragm ent of 503 by of the hmg gene derived from genomic DNA was obtained using t he polymerase chain reaction (PCR) and used as a probe to analyze the hmg g ene copy number and expression pattern. Southern blot analysis suggested th at hmg is encoded by a multigene family. Among the different plant tissues, the highest specific enzyme activity was observed in seeds, particularly a t the immature stage when it was 3.6-fold higher than in the mature seed. T hese data correlated with those of transcript accumulation, suggesting HMGR activity during seed development is under transcriptional control.