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A pathogen-responsive gene cluster for the production of highly modified fatty acids in tomato

ABSTRACT: In response to biotic stress, plants produce suites of highly modified fatty acids that bear unusual chemical functionality. Despite their chemical complexity and proposed roles in pathogen defense, little is known about the biosynthesis of these decorated fatty acids in plants. Falcarindiol is a prototypical acetylenic lipid present in carrot, tomato, and celery that inhibits growth of fungi and human cancer cell lines. Using a combination of untargeted metabolomics and RNA sequencing, we discovered a biosynthetic gene cluster in tomato (Solanum lycopersicum) that is required for the production of falcarindiol in response to an adapted fungal pathogen, Cladosporium fulvum. By reconstituting the initial biosynthetic steps in a heterologous host (Nicotiana benthamiana) and generating transgenic pathway mutants in tomato, we demonstrate a direct role for three genes in the cluster in falcarindiol biosynthesis. This work reveals a mechanism by which plants sculpt their lipid pool in response to pathogens, and provides critical insight into the complex biochemistry of alkynyl lipid production.

ORGANISM(S): Solanum lycopersicum

PROVIDER: GSE123543 | GEO | 2020/01/09

REPOSITORIES: GEO

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Project description:In plants, fatty acids are de novo synthesized predominantly in plastids fromacetyl-CoA. Although fatty acid biosynthesis has been biochemically well-studied, little isknown about the regulatory mechanisms of the pathway. Here, we show that overexpressionof the Arabidopsis (Arabidopsis thaliana) LEAFY COTYLEDON1 (LEC1) gene causesglobally increased expression of fatty acid biosynthetic genes, which are involved in keyreactions of condensation, chain elongation and desaturation of fatty acid biosynthesis. Inthe plastidial fatty acid synthetic pathway, over 58% of known enzyme-coding genes areupregulated in LEC1-overexpressing transgenic plants, including those encoding threesubunits of acetyl-CoA carboxylase, a key enzyme controlling the fatty acid biosynthesisflux. Moreover, genes involved in glycolysis and lipid accumulation are also upregulated.Consistent with these results, levels of major fatty acid species and lipids were substantiallyincreased in the transgenic plants. Genetic analysis indicates that the LEC1 function ispartially dependent on ABSCISIC ACID INSENSITIVE3, FUSCA3 and WRINKLED1 in theregulation of fatty acid biosynthesis. Moreover, a similar phenotype was observed intransgenic Arabidopsis plants overexpressing two LEC1-like genes of Brassica napus.These results suggest that LEC1 and LEC1-like genes act as key regulators to coordinate theexpression of fatty acid biosynthetic genes, thereby representing a promising target forgenetic improvement of oil-production plants. Experiment Overall Design: The pER8-LEC1 transgenic seedlings were germinated and grown in the presence of 10 ÂµM estradiol for 4 days. The control sample was germinated and grown under the identical conditions without estradiol but containing 0.1% DMSO. Total RNA was prepared from fresh or frozen plant materials using the RNAeasy Plant Mini Kit (Qiagen China, Beijing). The first strand cDNA was synthesized, and then hybridized with the ATH1 oligonucleotide chips as described by the manufactureâs instructions (Affymetrix). The microarray hybridization data were collected and analyzed using related R (http://www.r-project.org/) packages provided by Bioconductor (http://www.biocoductor.org/). In brief, genes differentially expressed between wild type and mutant plants were selected by first removing âabsentâ genes which were never detected to be expressed in the experiments, then a two-side t-test was applied to remaining genes in order to test the expression difference between wide type and mutant plants. To avoid multiple testing problems, raw p-values were then adjusted into False Discovery Rate (FDR) using Benjamini and Hochberg approach. Finally, differentially expressed genes were defined as those FDR less than 0.2. Functional analysis of differentially expressed genes was carried out using the biological process category of Arabidopsis Gene Ontology. The hierarchical map of GO annotation was constructed according to the ontology tree provided by the Gene Ontology website (http://www.geneontology.com) as described previously (Zheng and Wang, 2008). Ontology categories that are significantly enriched among differentially expressed genes (hypergeometric test and FDR less than 0.1) were displayed as boxes in the map.

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A pathogen-responsive gene cluster for the production of highly modified fatty acids in tomato

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