RESUMO
Flowers are essential but vulnerable plant organs, exposed to pollinators and florivores; however, flower chemical defenses are rarely investigated. We show here that two clustered terpene synthase and cytochrome P450 encoding genes (TPS11 and CYP706A3) on chromosome 5 of Arabidopsis (Arabidopsis thaliana) are tightly coexpressed in floral tissues, upon anthesis and during floral bud development. TPS11 was previously reported to generate a blend of sesquiterpenes. By heterologous coexpression of TPS11 and CYP706A3 in yeast (Saccharomyces cerevisiae) and Nicotiana benthamiana, we demonstrate that CYP706A3 is active on TPS11 products and also further oxidizes its own primary oxidation products. Analysis of headspace and soluble metabolites in cyp706a3 and 35S:CYP706A3 mutants indicate that CYP706A3-mediated metabolism largely suppresses sesquiterpene and most monoterpene emissions from opening flowers, and generates terpene oxides that are retained in floral tissues. In flower buds, the combined expression of TPS11 and CYP706A3 also suppresses volatile emissions and generates soluble sesquiterpene oxides. Florivory assays with the Brassicaceae specialist Plutella xylostella demonstrate that insect larvae avoid feeding on buds expressing CYP706A3 and accumulating terpene oxides. Composition of the floral microbiome appears also to be modulated by CYP706A3 expression. TPS11 and CYP706A3 simultaneously evolved within Brassicaceae and form the most versatile functional gene cluster described in higher plants so far.plantcell;31/12/2947/FX1F1fx1.
Assuntos
Alquil e Aril Transferases/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Sistema Enzimático do Citocromo P-450/metabolismo , Flores/metabolismo , Terpenos/antagonistas & inibidores , Alquil e Aril Transferases/genética , Animais , Arabidopsis/enzimologia , Arabidopsis/genética , Arabidopsis/microbiologia , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Sistema Enzimático do Citocromo P-450/química , Sistema Enzimático do Citocromo P-450/genética , Flores/genética , Flores/microbiologia , Expressão Gênica , Larva , Microbiota , Modelos Moleculares , Simulação de Acoplamento Molecular , Monoterpenos/metabolismo , Mariposas , Família Multigênica , Filogenia , Sesquiterpenos/metabolismo , Terpenos/química , Terpenos/metabolismo , Nicotiana/metabolismo , Leveduras/metabolismoRESUMO
RNA silencing is a natural defence mechanism against viruses in plants, and transgenes expressing viral RNA-derived sequences were previously shown to confer silencing-based enhanced resistance against the cognate virus in several species. However, RNA silencing was shown to dysfunction at low temperatures in several species, questioning the relevance of this strategy in perennial plants such as grapevines, which are often exposed to low temperatures during the winter season. Here, we show that inverted-repeat (IR) constructs trigger a highly efficient silencing reaction in all somatic tissues in grapevines. Similarly to other plant species, IR-derived siRNAs trigger production of secondary transitive siRNAs. However, and in sharp contrast to other species tested to date where RNA silencing is hindered at low temperature, this process remained active in grapevine cultivated at 4°C. Consistently, siRNA levels remained steady in grapevines cultivated between 26°C and 4°C, whereas they are severely decreased in Arabidopsis grown at 15°C and almost undetectable at 4°C. Altogether, these results demonstrate that RNA silencing operates in grapevine in a conserved manner but is resistant to far lower temperatures than ever described in other species.