Artemisinin is a plant natural product produced by Artemisia annua and the active ingredient in the most effective treatment for malaria. Efforts to eradicate malaria are increasing demand for an affordable, high-quality, robust supply of artemisinin. We performed deep sequencing on the transcriptome of A. annua to identify genes and markers for fast-track breeding. Extensive genetic variation enabled us to build a detailed genetic map with nine linkage groups. Replicated field trials resulted in a quantitative trait loci (QTL) map that accounts for a significant amount of the variation in key traits controlling artemisinin yield. Enrichment for positive QTLs in parents of new high-yielding hybrids confirms that the knowledge and tools to convert A. annua into a robust crop are now available.

Benzoates are a class of natural products containing compounds of industrial and strategic importance. In plants, the compounds exist in free form and as conjugates to a wide range of other metabolites such as glucose, which can be attached to the carboxyl group or to specific hydroxyl groups on the benzene ring. These glucosylation reactions have been studied for many years, but to date only one gene encoding a benzoate glucosyltransferase has been cloned. A phylogenetic analysis of sequences in the Arabidopsis genome revealed a large multigene family of putative glycosyltransferases containing a consensus sequence typically found in enzymes transferring glucose to small molecular weight compounds such as secondary metabolites. Ninety of these sequences have now been expressed as recombinant proteins in Escherichia coli, and their in vitro catalytic activities toward benzoates have been analyzed. The data show that only 14 proteins display activity toward 2-hydroxybenzoic acid, 4-hydroxybenzoic acid, and 3,4-dihydroxybenzoic acid. Of these, only two enzymes are active toward 2-hydroxybenzoic acid, suggesting they are the Arabidopsis salicylic acid glucosyltransferases. All of the enzymes forming glucose esters with the metabolites were located in Group L of the phylogenetic tree, whereas those forming O-glucosides were dispersed among five different groups. Catalytic activities were observed toward glucosylation of the 2-, 3-, or 4-hydroxyl group on the ring. To further explore their regioselectivity, the 14 enzymes were analyzed against benzoic acid, 3-hydroxybenzoic acid, 2,3-, 2,4-, 2,5-, and 2,6-dihydroxybenzoic acid. The data showed that glycosylation of specific sites could be positively or negatively influenced by the presence of additional hydroxyl groups on the ring. This study provides new tools for biotransformation reactions in vitro and a basis for engineering benzoate metabolism in plants.

Thermobia domestica belongs to an ancient group of insects and has a remarkable ability to digest crystalline cellulose without microbial assistance. By investigating the digestive proteome of Thermobia, we have identified over 20 members of an uncharacterized family of lytic polysaccharide monooxygenases (LPMOs). We show that this LPMO family spans across several clades of the Tree of Life, is of ancient origin, and was recruited by early arthropods with possible roles in remodeling endogenous chitin scaffolds during development and metamorphosis. Based on our in-depth characterization of Thermobia’s LPMOs, we propose that diversification of these enzymes toward cellulose digestion might have endowed ancestral insects with an effective biochemical apparatus for biomass degradation, allowing the early colonization of land during the Paleozoic Era. The vital role of LPMOs in modern agricultural pests and disease vectors offers new opportunities to help tackle global challenges in food security and the control of infectious diseases.

SummaryA glucosyltransferase (GT) of Arabidopsis, UGT71B6, recognizing the naturally occurring enantiomer of abscisic acid (ABA) in vitro, has been used to disturb ABA homeostasis in planta. Transgenic plants constitutively overexpressing UGT71B6 (71B6-OE) have been analysed for changes in ABA and the related ABA metabolites abscisic acid glucose ester (ABA-GE), phaseic acid (PA), dihydrophaseic acid (DPA), 7¢-hydroxyABA and neo-phaseic acid. Overexpression of the GT led to massive accumulation of ABA-GE and reduced levels of the oxidative metabolites PA and DPA, but had marginal effect on levels of free ABA. The control of ABA homeostasis, as reflected in levels of the different metabolites, differed in the 71B6-OEs whether the plants were grown under standard conditions or subjected to wilt stress. The impact of increased glucosylation of ABA on ABA-related phenotypes has also been assessed. Increased glucosylation of ABA led to phenotypic changes in post-germinative growth. The use of two structural analogues of ABA, known to have biological activity but to differ in their capacity to act as substrates for 71B6 in vitro, confirmed that the phenotypic changes arose specifically from the increased glucosylation caused by overexpression of 71B6. The phenotype and profile of ABA and related metabolites in a knockout line of 71B6, relative to wild type, has been assessed during Arabidopsis development and following stress treatments. The lack of major changes in these parameters is discussed in the context of functional redundancy of the multigene family of GTs in Arabidopsis.

Many organisms adapted to live at subzero temperatures express antifreeze proteins that improve their tolerance to freezing. Although structurally diverse, all antifreeze proteins interact with ice surfaces, depress the freezing temperature of aqueous solutions, and inhibit ice crystal growth. A protein purified from carrot shares these functional features with antifreeze proteins of fish. Expression of the carrot complementary DNA in tobacco resulted in the accumulation of antifreeze activity in the apoplast of plants grown at greenhouse temperatures. The sequence of carrot antifreeze protein is similar to that of polygalacturonase inhibitor proteins and contains leucine-rich repeats.