Craig Schenck (Last Lab)

  • Oct 29, 2019

Date & Location: October 29, 2019, at 12p; Room 168 Plant Biology Building

Subject: Biochemical Pathway Leading to Phylogenetically Restricted Acylsugars in Nicotiana acuminata

Abstract: Sugar esters (acylsugars) are defensive, trichome-localized metabolites produced primarily within the Solanaceae family. Depending on the species, up to five acyl chains are esterified at various positions on the sugar core, typically sucrose. Due to acyl chain length and branching variation, tremendous acylsugar structural diversity exists within the Solanaceae. This diversity is better characterized in the Solanum genus relative to other lineages.

To gain insight into acylsugar diversity outside Solanum, we characterized acylsugar profiles and the underlying biosynthetic pathway in the Nicotiana genus. Acylsugar profiles were screened from leaf dips using LC- and GC-MS, and acyl chain types were mapped onto a Nicotiana phylogeny. Most acyl chain types are present in all Nicotiana species, however some are restricted to closely-related lineages. For example, a unique acyl chain type, tiglic acid, was found in a single Nicotiana species (Nicotiana acuminata) and represents up to 80% of all acyl chains on the acylsugars in two of the four N. acuminata accessions screened. NMR structural determination of two purified acylsugars from N. acuminata showed that they had a total of four and five acylations on a sucrose core, of which two were tiglic acid. A comparative RNA-seq analysis of trichomes and stem tissue from a high tiglyl-acylsugar producing accession revealed that homologs of acylsugar biosynthetic genes in tomato were highly enriched in the trichomes. Enzyme assays with four trichome-enriched BAHD acyltransferase enzymes together with acyl-CoAs and sucrose produced tetraacylated sucrose, suggesting that these four enzymes represent a complete acylsugar biosynthetic pathway.

Future work will test the activity of these enzymes with in vivo acyl-CoAs as the in vitro enzyme assay-produced tetraacylated sucroses did not match those found in planta. Further analysis will determine the biochemical mechanism underlying high tiglyl-acylsugar production in some N. acuminata accessions.

Speaker Lab: Dr. Robert L. Last