We identified 11 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) that occur in concentrations equivalent to starch (mg/g fresh mass) in aboveground tissues of coyote tobacco (Nicotiana attenuata) and differ in their sugar moieties and malonyl sugar esters (0-2). Concentrations of HGL-DTGs, particularly malonylated compounds, are highest in young and reproductive tissues. Within a tissue, herbivore elicitation changes concentrations and biosynthetic kinetics of individual compounds. Using stably transformed N. attenuata plants silenced in jasmonate production and perception, or production of N. attenuata Hyp-rich glycopeptide systemin precursor by RNA interference, we identified malonylation as the key biosynthetic step regulated by herbivory and jasmonate signaling. We stably silenced N. attenuata geranylgeranyl diphosphate synthase (ggpps) to reduce precursors for the HGL-DTG skeleton, resulting in reduced total HGL-DTGs and greater vulnerability to native herbivores in the field. Larvae of the specialist tobacco hornworm (Manduca sexta) grew up to 10 times as large on ggpps silenced plants, and silenced plants suffered significantly more damage from herbivores in N. attenuata9s native habitat than did wild-type plants. We propose that high concentrations of HGL-DTGs effectively defend valuable tissues against herbivores and that malonylation may play an important role in regulating the distribution and storage of HGL-DTGs in plants.

Significance: Population geneticists have educated molecular biologists in how to harness the statistical power of variance arising from interindividual natural variation to elucidate gene function in plants. The metabolic differences among tissues within a plant provide another source of variance that can be harnessed in the quest to understand gene function. We combine the power of information theory statistics and computational metabolomics to parse metabolic diversity within an ecological model plant, Nicotiana attenuata , to reveal intriguing patterns of metabolic specialization in floral limb and anthers, the responsible mechanisms of which we parse further by detecting and silencing the expression of two UDP-glycosyltransferases involved in floral flavonoid metabolism. The workflow defines a framework for future evolutionary studies on plant tissue metabolic specialization.

Diterpenoids inhibit lipid biosynthesis: Plants make a variety of molecules that serve to protect them against hungry insects. Li et al. analyzed the balance between plants defending themselves and plants poisoning themselves. In wild tobacco ( Nicotiana attenuata ), two cytochrome P450 enzymes work within the biosynthetic pathway of 17-hydroxygeranyllinalool diterpene glycosides to help prevent the accumulation of toxic diterpene derivatives. Those same diterpene derivatives are formed in an insect herbivore after ingestion and cause toxicity by inhibiting sphingolipid biosynthesis in both plant and insect. Science , this issue p. 255