The cis-prenyltransferase protein family in Taraxacum koksaghyz

Abstract

The cis-prenyltransferase (cisPT) enzyme family is involved in diverse biological processes that require the synthesis of linear isoprenoid compounds. Taraxacum koksaghyz is a rubber-producing species and potential crop that has eight cisPT homologs (TkCPT1–8) but their distribution and functions are unclear. We compared the structural organization and sequence homology of the proteins, and defined two groups: TkCPT and TkCPT-like (TkCPTL) proteins that form heteromeric cisPT enzymes (TkCPT1–4), and TkCPT proteins that function as homomeric cisPTs (TkCPT5–8). We found that TkCPT1 and TkCPT2 are predominantly expressed in latex whereas TkCPT3 and TkCPT6-8 are predominantly expressed in leaves. TkCPT4 was constitutively expressed in all T. koksaghyz tissues and TkCPT5 mRNA was detected in flowers. The TkCPT1–4 subunits localized to the endoplasmic reticulum whereas TkCPT5–7 were located in chloroplasts. TkCPT1-4 interacted with TkCPTL1-2, forming heteromeric complexes that complemented yeast lacking cisPT. Homomeric TkCPT6 could also complement yeast lacking cisPT but we observed no cisPT activity for TkCPT5, TkCPT7, or TkCPT8 in yeast functional complementation assays. TkCPT1/TkCPTL1 and TkCPT2/TkCPTL1 expressed in yeast produced extra-long-chain polyisoprenes, whereas TkCPT3/TkCPTL1 and TkCPT4/TkCPTL1 produced long-chain dolichols and polyisoprenes, TkCPT5 and TkCPT6 produced medium-chain polyisoprenes, and TkCPT7 and TkCPT8 catalyzed the formation of nerol. The complexity of cisPT proteins in T. koksaghyz suggests that they synthesize different metabolites in a tissue-specific manner, and thus play distinct roles in isoprenoid metabolism. This is the first comprehensive analysis of the localization, interactions, and products of the entire T. koksaghyz cisPT family in vivo, also revealing a novel pentaprenol found specifically in flowers.