|PENG, HUI - Guangxi Normal University|
|WHITAKER, BRUCE - Retired ARS Employee|
|SHANGGUAN, LINGFEI - Nanjing Agricultural University|
|DONG, WEN - University Of Tennessee|
Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2016
Publication Date: 12/7/2016
Citation: Peng, H., Yang, T., Whitaker, B.D., Trouth, F.J., Shangguan, L., Dong, W., Jurick II, W.M. 2016. Characterization of spermidine hydroxycinnamoyl transferases from eggplant (Solanum melongena L.) and its wild relative Solanum richardii Dunal. Horticulture Research. 3:16062. doi: 10.1038/hortres.2016.62.
Interpretive Summary: Hydroxycinnamic acid amides (HCAAs) are a class of phytochemicals which have anticarcinogenic, antihypertensive, antimicrobial, and other potentially therapeutic activities. Eggplant produces a variety of HCAAs. These HCAAs are important in plant development and adaptation to environmental changes. However, the identities of the genes responsible for the HCAA biosynthesis are not clear. This study reports the isolation and characterization of a spermidine hydroxycinnamoyl transferase (SHT) from eggplant (Solanum melongena) and its wild relative S. richardii, respectively. They are designated as SmSHT and SrSHT. Both SHT share high homology with just five amino acid changes. They have the similar preference for substrate selection. However, SrSHT from the wild eggplant displayed higher activity than SmSHT from eggplant. It is possible that two key amino acid changes in SrSHT altered the enzyme activity. These results provide a platform to obtain HCAA rich fruits for eggplant and other solanaceous crops.
Technical Abstract: Eggplant produces a variety of hydroxycinnamic acid amides (HCAAs) that play an important role in plant development and adaptation to environmental changes. However, the HCAA pathway remains largely uncharacterized in Solanaceae. In this study, a spermidine hydroxycinnamoyl transferase (SHT) from eggplant (Solanum melongena) and its wild relative S. richardii were identified and characterized, and designated as SmSHT and SrSHT, respectively. Both SHT had extremely high identity (98.9%) with just five amino acid substitutions. Recombinant SmSHT catalyzed the synthesis of mono-, bi- and triacylated polyamines. Using caffeoyl-CoA as theacyl donor, SmSHT preferred spermidine as the acyl acceptor. However, it also utilized spermine and putrescine with 23% and 8% of the activity in relative to using spermidine. When spermidine was the acyl acceptor, the donor preference order for SmSHT was caffeoyl-CoA (100%) > feruloyl-CoA (65%) > p-coumaroyl-CoA (49%). SrSHT exhibited the same substrate specificity as SmSHT, yet exhibited significantly higher catalytic activity than SmSHT. For example, using caffeoyl-CoA and spermidine, the Kcat of SrSHT(606.8 ± 29.0min-1) was 37.3% higher than SmSHT (441.8 ± 11.1min-1). Based on structure modeling, five substitutions in SrSHT might result in four alterations in their predicted 3D structure. In particular, the conserved Lys402 adjacent to the DFGWG motif, and Cys200 in the crossover loop in SmSHT were replaced by Glu and Ser in SrSHT. These substitutions may contribute to the enhanced activity in SrSHT. Our results provide a platform to generate HCAA rich fruits for eggplant and other solanaceous crops.