Characterization of cDNA and genomic clones encoding 3-hydroxy-3-methylglutaryl-coenzyme A reductase from Hevea brasiliensis.

Hevea brasiliensis is the major producer of natural rubber which is cis-1,4-polyisoprene. The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) is involved in the biosynthesis of rubber and other plant products. We have used a hamster HMGR cDNA clone as a heterologous hybridization probe to isolate and characterize cDNA and genomic clones of HMGR from H. brasiliensis. Sequence analysis revealed that these clones fall into two different classes, HMGR1 and HMGR2. Comparison of the two classes shows 86% nucleotide sequence homology and 95% amino acid homology. The carboxy-termini of Hevea HMGRs are highly homologous to those of hamster, yeast and Arabidopsis HMGR. The amino-terminus of Hevea HMGR contains two potential membrane-spanning domains as in Arabidopsis HMGR while seven such domains are found in the HMGRs of other organisms. The apparent molecular mass of Hevea HMGR was estimated in western blot analysis to be 59 kDa. Northern blot analysis indicated that the HMGR1 transcript of 2.4 kb is more highly-expressed in laticifer than in leaf. Genomic Southern analysis using 3'-end cDNA probes indicates the presence of at least two HMGR genes in Hevea.