American Society of Plant Biologists 
Isoprene synthase and the relationship to the terpene synthase family
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Minisymposium: Secondary Metabolism

Abs # 37003: Isoprene synthase and the relationship to the terpene synthase family

Presenter: Yeh, Sansun ,
Gong, Deming  (B)   Sharkey, Thomas D. (A)  
Affiliations: (A): Dept. Botany, Univ. Wisc. Madison, Madison WI 53706
(B): Department of Plant Biology, The University of Arizona, Tucson, AZ 85721

Isoprene is emitted from many but not all plants. Isoprene synthase uses DMAPP to make isoprene inside chloroplasts. Isoprene synthase has now been cloned from three species and in two cases both genomic and cDNA sequences are available. Isoprene synthase is similar to monoterpene synthases of angiosperms and is clearly part of the terpene synthase family of genes. To understand how isoprene synthase fits in this family, we examined its genomic structure and compared it with other members of the terpene synthase gene family. The genomic sequence for isoprene synthase was obtained using a PCR based cloning technique from aspen and kudzu (both isoprene emitters). The kudzu isoprene synthase cDNA sequence was cloned and purified from E. coli and showed isoprene synthase activity. Isoprene synthase from aspen was 96% identical to isoprene synthase from hybrid poplar which had been shown to make isoprene (Miller et al. Planta 213:483-487, 2001). Aspen and kudzu isoprene synthases are only 51.6% identical at the protein level. As with the class III terpene synthase genes (classified by Trapp and Croteau [Genetics 158:811-832, 2001]), both isoprene synthase genes have 7 exons and 6 introns. The exon and intron sizes are somewhat conserved between the two isoprene synthase genes. As postulated by Back and Chappell (JBC 270:7375-7381, 1996), the terpene synthases may have evolved by domain swapping. The sequences were translated and aligned exon by exon to examine this possibility. The isoprene synthase sequences were also compared to the genomic structures of the two most closely related Arabidopsis monoterpene synthases. The highest similarity came from aligning exons 4 and 5. Exon 4 is thought to be involved in substrate binding and catalysis and contains the conserved Mg2+ binding domain. A phylogenetic relationship was drawn for these sequences with all of the known and putative terpene synthases from Arabidopsis. These sequences were also compared to other known monoterpene synthase genomic sequences. The isoprene synthases appears to be more closely related to each other than to other terpene synthases from Arabidopsis or other species.

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