BAHD family acyltransferases
From Purdue Genomics Database Facility
Nicholas D. Bonawitz (nbonawit@purdue.edu) and Clint Chapple (chapple@purdue.edu)
Department of Biochemistry, Purdue University, West Lafayette, IN, USA.
Contents |
Summary
BAHD acyltransferases are a recently described class of enzymes responsible for the formation of a great variety of secondary metabolites throughout the plant kingdom1. Members of this family take an activated carboxylic acid (in this case the CoA thioester form of the acid) as an acyl donor and either an alcohol or, more rarely, a primary amine as an acyl acceptor, catalyzing the formation of an ester or an amide bond, respectively. The acyl donors and acyl acceptors taken as substrates by BAHD acyltransferases are quite diverse, and different BAHD family members show a range of substrate specificities. Products produced by characterized family members include modified anthocyanins2,3,4,5,6, green-leaf volatiles (thought to be involved in anti-herbivory)7, and lignin biosynthetic intermediates8. Also, some BAHD acyltransferases are essential for the synthesis of high value plant metabolites such as taxol and taxol analogs9,10 as well as volatile esters conferring flavor and odor to fruits and flowers11,12. However, the great majority of BAHD acyltransferases are uncharacterized and thus the nature of their substrates and products is unknown. Coupled with the fact that many plant genomes appear to encode a large number of these enzymes (e.g. more than 60 in Arabidopsis or 100 in grasses), the range of secondary metabolites produced by BAHD family members has only begun to be understood.
The characterized members of the BAHD family have recently been divided into 5 distinct clades on the basis of phylogenetic analysis1. Interestingly, although these clades do not perfectly separate enzymes with different functions, it does appear that members of the same clade may share some characteristics regarding function and substrate specificity. For example, characterized clade I enzymes predominantly take anthocyanins as acyl donors and malonate as an acyl acceptor2,3,4,5,6, whereas clade III enzymes tend to act as acetyltransferases taking a range of acyl acceptors12,13,14. Also, several members of clade III act in the production of volatile esters. Clade II is the least understood, and the activities of its two members are not known, having been identified on the basis of a mutant phenotype only15,16,17. Clade V enzymes appear diverse in function, though many take hydroxycinnamic acids or benzoic acid as acyl donors8,12,18,19,20. Clade IV contains only a single member, encoding an agmatine hydroxycinnamoyl transferase21.
Below, we list the BAHD family members in Selaginella with links to their pages on the JGI website. We have grouped these enzymes into five groups, labeled A through E. Also shown at right is a phylogenetic tree containing all of the characterized BAHD acyltransferases, as well as all BAHD family members from Arabidopsis, Selaginella, and Physcomitrella. Interestingly, although Physcomitrella possesses only around ten BAHD acyltransferases, the Selaginella genome encodes almost as many BAHD family members as does the Arabidopsis genome. Clades I, IV, and V appear to be ancient enzymes and correspond to Groups A, B, and E in the Selaginella genome. However, much of the diversification of the BAHD acyltransferases appears to have occurred after the divergence of Arabidopsis and Selaginella, as the Selaginella genome contains no Clade III and no clade II family members. Conversely, Group C and Group B appear Selaginella-specific. The large group B in particular has apparently arisen as a result of multiple gene duplications in the lineage leading to Selaginella, leading to large arrays of duplicated genes (and pseudogenes) on scaffolds 63 and 38 (BAHDb7 sequences) as well as scaffolds 149, 4, and 417 (BAHDb6, BAHDb8, and BAHDb9 sequences). In many cases, only one allele appears to encode a functional acyltransferase, while the corresponding locus on the sister scaffold often apparently contains an inactivating premature stop codon or frameshift mutation. The independent diversification of the BAHD acyltransferase family in Selaginella suggests that secondary metabolism in this lineage could be substantially different than that seen in angiosperms, and opens up the potential for discovery new compounds or even classes of compounds in these species. Future studies of these enzymes should yield insight into the diversity and evolution of plant secondary metabolism.
List of Selaginella BAHD acyltransferases
Group A
BAHDa2a-1, BAHDa2b-1, BAHDa2a-2
BAHDa6a-1, BAHDa6b-1, BAHDa6-2
Group B
BAHDb5a-1, BAHDb5b-1, BAHDb5a-2, BAHDb5b-2, BAHDb5c
BAHDb7a-1, BAHDb7b-1, BAHDb7a-2, BAHDb7b-2, BAHDb7c, BAHDb7d
BAHDb9a, BAHDb9b, BAHDb9c-1, BAHDb9c-2
Group C
Group D
Group E
References
1. D'Auria JC. Curr Opin in Plant Biol 2006, 9:331-340
2. Suzuki H et al. Plant Biotechnol 2003 20:229-234
3. Suzuki H et al. Plant Sci 2004 166:89-96
4. Suzuki H et al. J Mol Catal B Enzym 2004, 28:87-93
5. Yonekura-Sakakibara K et al. Plant Cell Physiol 2000, 41:495-502
6. Suzuki H et al. J Biol Chem 2001, 276:49013-49019
7. D'Auria JC et al. Plant J 2007, 49:194-207
8. Hoffman L et al. J Biol Chem 2003, 278:95-103
9. Walker K et al. Proc Natl Acad Sci USA 2002, 99:12715-12720
10. Walker K and Croteau R. Proc Natl Acad Sci USA 2000, 97:583-587
11. Dexter R et al. Plant J 2007, 49:265-275
12. El-Sharkawy I et al. Plant Mol Biol 2005, 59:345-362
13. Dudareva N et al. Plant J 1998, 14:297-304
14. D'Auria JC et al. Plant Physiol 2002, 130:466-476
15. Negruk V et al. Plant J 1996, 9:137-145
16. Xia Y et al. Plant Cell 1996, 8:1291-1304
17. Tacke E et al. Plant J 1995, 8:907-917
18. Beekwilder J et al. Plant Physiol 2004, 135:1865-1878
19. Yang Q et al. Plant Mol Biol 1997, 35:777-789
20. Yang Q et al. Mol Plant Microbe Interact 2004, 17:81-89
21. Burhenne K et al. J Biol Chem 2003, 278:13919-13927
