摘要：The genome sequencing project revealed presence of two active chalcone synthase (CHS) homologues ( At1g02050 and At4g34850 ) in the model plant Arabidopsis thaliana . We report herein the two genes encode closely related novel plant-specific type III polyketide synthases (PKSs) that produces long-chain alkyl α-pyrones. PKS-A ( At1g02050 ) and PKS-B ( At4g34850 ) share significantly low amino acid sequence identity (20—40%) with other type III PKSs, and the phylogenetic tree analysis revealed that they form a separate cluster located closely to those of bacterial type III PKSs. When expressed in Escherichia coli , both PKS-A and PKS-B accepted unusually long (up to the C20 chain-length) fatty acyl CoAs as a starter substrate, and carried out sequential condensations with malonyl-CoA to produce triketide and tetraketide α-pyrones. Interestingly, despite the low sequence identity, homology modeling revealed that the active-site architecture of PKS-A and PKS-B showed similarity to that of a bacterial type III PKS from Mycobacterium tuberculosis .
关键词：Arabidopsis thaliana;type III polyketide synthase;chalcone synthase;long-chain α-pyrone;pyrone lipid;homology modeling
