| dc.description.abstract | Plant metabolites are sub-divided into two classes- primary and secondary or specialized metabolites. Acylsugars are specialized metabolites secreted by many members of the nightshade family (Solanaceae). These compounds are branched-chain and straight-chain fatty acids esterified to glucose or sucrose. Acylsugars have important roles in plant defense and potential commercial applications. However, several acylsugar metabolic genes remain unidentified, and little is known about regulation of this pathway. Using transcriptomics approaches, acylsugar metabolic genes were identified in a wild tomato species (Solanum pennellii). Differential gene expression analyses between low- and high-acylsugar-producing accessions of Solanum pennellii revealed that expression levels of known and novel candidate genes (putatively encoding betaketoacyl-(acyl-carrier-protein) synthases, peroxisomal acyl-activating enzymes, ABC transporters, and central carbon metabolic proteins) were positively correlated with acylsugar accumulation, except two genes previously reported to be involved in acylglucose biosynthesis. Genes putatively encoding oxylipin metabolic proteins, subtilisin-like proteases, and other antimicrobial defense proteins were upregulated in low-acylsugar-producing accessions, possibly to compensate for diminished defense activities of acylsugars. Transcriptome analysis after biochemical inhibition of biosynthesis of branched-chain amino acids (precursors to branched-chain fatty acids) by imazapyr showed concentration-dependent downregulation of known and most acylsugar candidate genes, but not defense genes. Weighted gene correlation network analysis identified separate co-expressed gene networks for acylsugar metabolism (including six transcription factor genes and flavonoid metabolic genes) and plant defense (including genes putatively encoding NB-ARC and leucine-rich repeat sequences, protein kinases and defense signaling proteins, and previously mentioned defense proteins). Acylsugars are secreted through trichomes, and virus-induced gene silencing of two trichome preferentially expressed candidate genes for straight-chain fatty acid biosynthesis confirmed their role in acylsugar metabolism. This work will serve as a valuable genetic resource for increasing our understanding of acylsugar metabolism and defense in Solanum pennellii and other plants. | en |
