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The evolution of chemical complexity has been a major driver of plant diversification, with novel compounds serving as key innovations. The species-rich mint family (Lamiaceae) produces an enormous variety of compounds that act as attractants and defense molecules in nature and are used widely by humans as flavor additives, fragrances, and anti-herbivory agents. To elucidate the mechanisms by which such diversity evolved, we combined leaf transcriptome data from 48 Lamiaceae species and four outgroups with a robust phylogeny and chemical analyses of three terpenoid classes (monoterpenes, sesquiterpenes, and iridoids) that share and compete for precursors. Our integrated chemical–genomic–phylogenetic approach revealed that: (1) gene family expansion rather than increased enzyme promiscuity of terpene synthases is correlated with mono- and sesquiterpene diversity; (2) differential expression of core genes within the iridoid biosynthetic pathway is associated with iridoid presence/absence; (3) generally, production of iridoids and canonical monoterpenes appears to be inversely correlated; and (4) iridoid biosynthesis is significantly associated with expression of geraniol synthase, which diverts metabolic flux away from canonical monoterpenes, suggesting that competition for common precursors can be a central control point in specialized metabolism. These results suggest that multiple mechanisms contributed to the evolution of chemodiversity in this economically important family. The mint family (Lamiaceae) includes many culturally and economically important species and collectively exhibits an exceptionally high degree of chemical diversity. Using an integrated chemical-genomic-phylogenetic approach, gene family expansion, altered gene expression of key biosynthetic pathway genes, and flux of precursors were shown to underlie the evolution of chemodiversity observed in this chemically rich clade.

Chapter 1 of this dissertation provides background information into the two plant terpenoid biosynthetic pathways, the mevalonate (MVA) and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathways. These pathways are responsible for the formation of the five-carbon building blocks isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). These metabolites are then condensed to form various chains of C5x terpenoids. The diversity of terpenoids within the diverse Lamiaceae is also discussed. Chapter 2 looks at the role of a homolog of the archeal gene isopentenyl phosphate kinase (IPK) in plants. IPK is found in all sequenced plant genomes and acts in parallel with the canonical MVA pathway to produce IPP and DMAPP. IPK returns the dephosphorylated metabolites isopentenyl monophosphate (IP) and dimethylallyl monophosophate (DMAP), which act as inhibitors for downstream terpenoid biosynthesis, to IPP and DMAPP. Chapter 3 then looks at the perpetrator of dephosphorylated IPP and DMAPP by determining whether this is specific or non-specific phosphorylation. This chapter provides evidence that two members of the Nudix hydrolase family, Nudx1 and Nudx3, are responsible for this dephosphorylation. De novo biosynthesis of IP, via overexpression of the Roseiflexus castenholzii phosphomevalonate decarboxylase (MPD) suggests the importance of subcellular sequestration of terpenoid metabolites as well as the importance of phosphomevalonate kinase (PMK) on regulation of the MVA pathway. Chapter 4 determines the evolutionary relationship of terpenoid biosynthesis in the diverse Lamiaceae, or mint, family. Mints produce substantial quantities of mono- and sesquiterpenes and also produce geranyl pyrophosphate (GPP)-derived metabolites called iridoids. After surveying the metabolite profiles and transcriptome data from 48 mint species, there is evidence of correlation between those mint species producing iridoids and iridoid biosynthetic genes. Likewise, a strong correlation was discovered between the presence/absence of iridoids and expression of geraniol synthase (GES), the enzyme responsible for the branchpoint in the production of iridoids or canonical monoterpenes.

Found in all living organisms, terpenoids make up the largest group of natural products and are essential compounds for many major processes, including photosynthesis, respiration, hormone production, and electron transport. Additionally, they have commercial and medical value in products including fragrances, cosmetics, and medicines. Terpenoids originate from the five-carbon building blocks isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are synthesized by the mevalonic acid (MVA) and methylerithritol phosphate (MEP) pathways. An alternative MVA pathway was discovered in Archaea with the final two enzymes being phosphomevalonate decarboxylase (MPD) and isopentenyl phosphate kinase (IPK). Even though this alternative pathway is not present in plants, presence of IPK was retained. The overexpression of IPK in planta indicates that IPK plays a significant role in the MVA pathway by synthesizing IPP/DMAPP from an IP/DMAP pool for terpenoid biosynthesis. It has been suggested that this monophosphate pool regulates downstream carbon flux by inhibiting farnesyl diphosphate synthase (FPPS). By utilizing MPD from the archeabacterium Roseiflexus castenholzii, we can see how an increased isopentenyl (IP) pool affects downstream terpenoid biosynthesis. To do this, RcMPD was overexpressed in the background of Arabidopsis thaliana T-DNA insertion lines of a knockdown of IPK. These lines were tested for expression of MPD/IPK using qrt-PCR and terpenoids were analyzed via sterol extraction and scent collection. Levels of monoterpenes (MEP pathway products) and sesquiterpenes (MVA pathway products) were significantly reduced, suggesting that a larger monophosphate pool reduces downstream synthesis of farnesyl diphosphate, a precursor for sterol and sesquiterpene biosynthesis.

International audience; The link between personality and the interest of individuals for science has not been thoroughly explored. In this report, we studied psychopathological traits in students studying science in French top-ranking institutions. Three hundred and forty seven individuals answered questionnaires assessing autistic and schizotypal dimensions, as well as anxiety, depression symptomatology and attachment quality. A cluster analysis based on autistic and schizotypal traits led to the identification of 4 distinct profiles: a "low trait cluster", a "moderate autistic trait cluster", a "moderate schizotypal trait cluster" and a "high trait cluster" (HTC) composed of individuals with high scores on both autistic and schizotypal scales. Each cluster represented 20.1 to 27.1% of participants and was clearly different from the three others, both on autistic and on schizotypal dimensions. These groups could be also typified by their level of anxiety, depression or degraded attachment, which are proportional to the extent of psychopathological traits. Moreover, students from the HTC cluster displayed lower academic results, thus implying that autistic traits might impair success in science when they are associated with moderate schizotypal personality features. This study also suggests that depression and anxiety might mediate performance inhibition in the HTC group.

Isoprenoids are secondary metabolites that control numerous plant functions including signaling, growth, photosynthesis, and membrane structure. The bioengineering of isoprenoid synthesis could produce plants with a variety of beneficial traits. Plants form isoprenoids using two different pathways, the mevalonate (MVA) pathway and the methylerithritol phosphate (MEP) pathway, which cooperate via metabolic cross-talk. Transgenic tomato lines expressing both the plastidic and cytosolic forms of the snapdragon nerolidol/linalool terpene synthase under a fruit ripening specific promoter were transiently transformed to overexpress key enzymes in the two isoprenoid pathways. Hydroxymethylglutaryl-coenzyme A reductase (HMGR) is the rate limiting enzyme in the MVA pathway that was selected for overexpression. 1-deoxy-D-xylulose-5-phosphate synthase (DXPS) in the plastid was targeted as it is the first committed step in the MEP pathway. HMGR and DXPS coding regions were cloned into binary vectors under a constitutive promoter and introduced into Agrobacterium tumefaciens which were then injected into ripening tomato fruits for transient expression. Additionally, untransformed fruits were incubated with either the MVA-inhibitor mevinolin or the MEP-inhibitor fosmidomycin. Terpene production was characterized by gas chromatography and mass spectrometery of fruit volatiles collected at the ripe stage. Inhibitor treatment is expected to decrease terpene synthesis in the same compartment as the inhibited pathway. The overexpression of early MVA and MEP pathway genes is expected to significantly increase the formation of terpenes.