Specialized metabolism by trichome-enriched Rubisco and fatty acid synthase components.

Acylsugars, specialized metabolites with defense activities, are secreted by trichomes of many solanaceous plants. Several acylsugar metabolic genes (AMGs) remain unknown. We previously reported multiple candidate AMGs. Here, using multiple approaches, we characterized additional AMGs. First, we identified differentially expressed genes between high- and low-acylsugar-producing F2 plants derived from a cross between cultivated tomato (Solanum lycopersicum) and a wild relative (Solanum pennellii), which produce acylsugars that are ∼1% and ∼20% of leaf dry weight, respectively. Expression levels of many known and candidate AMGs positively correlated with acylsugar amounts in F2 individuals. Next, we identified lycopersicum-pennellii putative orthologs with higher nonsynonymous to synonymous substitutions. These analyses identified four candidate genes, three of which showed enriched expression in stem trichomes compared to underlying tissues (shaved stems). Virus-induced gene silencing confirmed two candidates, Sopen05g009610 [beta-ketoacyl-(acyl-carrier-protein) reductase; fatty acid synthase component] and Sopen07g006810 (Rubisco small subunit), as AMGs. Phylogenetic analysis indicated that Sopen05g009610 is distinct from specialized metabolic cytosolic reductases but closely related to two capsaicinoid biosynthetic reductases, suggesting evolutionary relationship between acylsugar and capsaicinoid biosynthesis. Analysis of publicly available datasets revealed enriched expression of Sopen05g009610 orthologs in trichomes of several acylsugar-producing species. Similarly, orthologs of Sopen07g006810 were identified as solanaceous trichome-enriched members, which form a phylogenetic clade distinct from those of mesophyll-expressed "regular" Rubisco small subunits. Furthermore, δ13C analyses indicated recycling of metabolic CO2 into acylsugars by Sopen07g006810 and showed how trichomes support high levels of specialized metabolite production. These findings have implications for genetic manipulation of trichome-specialized metabolism in solanaceous crops.

Candidate Gene Networks for Acylsugar Metabolism and Plant Defense in Wild Tomato Solanum pennellii.

Many solanaceous plants secrete acylsugars, which are branched-chain and straight-chain fatty acids esterified to Glu or Suc. These compounds 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. Comparative transcriptomics between low- and high-acylsugar-producing accessions of Solanum pennellii revealed that expression levels of known and novel candidate genes (putatively encoding beta-ketoacyl-(acyl-carrier-protein) synthases, peroxisomal acyl-activating enzymes, ATP binding cassette (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. 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 coexpressed 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). Additionally, virus-induced gene silencing of two trichomes preferentially expressed candidate genes for straight-chain fatty acid biosynthesis confirmed their role in acylsugar metabolism.

Astaxanthin inhibits gemcitabine-resistant human pancreatic cancer progression through EMT inhibition and gemcitabine resensitization.

Pancreatic cancer rapidly acquires resistance to chemotherapy resulting in its being difficult to treat. Gemcitabine is the current clinical chemotherapy strategy; however, owing to gemcitabine resistance, it is only able to prolong the life of patients with pancreatic cancer for a limited number of months. Understanding the underlying molecular mechanisms of gemcitabine resistance and selecting a suitable combination of agents for the treatment of pancreatic cancer is required. Astaxanthin (ASX) is able to resensitize gemcitabine-resistant human pancreatic cancer cells (GR-HPCCs) to gemcitabine. ASX was identified to upregulate human equilibrative nucleoside transporter 1 (hENT1) and downregulate ribonucleoside diphosphate reductase (RRM) 1 and 2 to enhance gemcitabine-induced cell death in GR-HPCCs treated with gemcitabine, and also downregulates TWIST1 and ZEB1 to inhibit the gemcitabine-induced epithelial-mesenchymal transition (EMT) phenotype in GR-HPCCs and to mediate hENT1, RRM1 and RRM2. Furthermore, ASX acts through the hypoxia-inducible factor 1α/signal transducer and activator of transcription 3 signaling pathway to mediate TWIST1, ZEB1, hENT1, RRM1 and RRM2, regulating the gemcitabine-induced EMT phenotype and gemcitabine-induced cell death. Co-treatment with ASX and gemcitabine in a tumor xenograft model induced by GR-HPCCs supported the in vitro results. The results of the present study provide a novel therapeutic strategy for the treatment of gemcitabine-resistant pancreatic cancer.

Glucose-free fructose production from Jerusalem artichoke using a recombinant inulinase-secreting Saccharomyces cerevisiae strain.

PURPOSE OF WORK: Using inulin (polyfructose) obtained from Jerusalen artichokes, we have produced fructose free of residual glucose using a recombinant inulinase-secreting strain of Saccharomyces cerevisiae in a one-step fermentation of Jerusalem artichoke tubers. For producing fructose from inulin, a recombinant inulinase-producing Saccharomyce cerevisiae strain was constructed with a deficiency in fructose uptake by disruption of two hexokinase genes hxk1 and hxk2. The inulinase gene introduced into S. cerevisiae was cloned from Kluyveromyces cicerisporus. Extracellular inulinase activity of the recombinant hxk-mutated S. cerevisiae strain reached 31 U ml(-1) after 96 h growth. When grown in a medium containing Jerusalem artichoke tubers as the sole component without any additives, the recombinant yeast accumulated fructose up to 9.2% (w/v) in the fermentation broth with only 0.1% (w/v) glucose left after 24 h.