A single MYB transcription factor with multiple functions during flower development.

Members of the R2R3-MYB transcription factor subgroup 19 (SG19) have been extensively studied in multiple plant species using different silenced or mutated lines. Some studies have proposed a function in flower opening, others in floral organ development/maturation, or specialized metabolism production. While SG19 members are clearly key players during flower development and maturation, the resulting picture is complex, confusing our understanding in how SG19 genes function. To clarify the function of the SG19 transcription factors, we used a single system, Petunia axillaris, and targeted its two SG19 members (EOB1 and EOB2) by CRISPR-Cas9. Although EOB1 and EOB2 are highly similar, they display radically different mutant phenotypes. EOB1 has a specific role in scent emission while EOB2 has pleiotropic functions during flower development. The eob2 knockout mutants reveal that EOB2 is a repressor of flower bud senescence by inhibiting ethylene production. Moreover, partial loss-of-function mutants (transcriptional activation domain missing) show that EOB2 is also involved in both petal and pistil maturation through regulation of primary and secondary metabolism. Here, we provide new insights into the genetic regulation of flower maturation and senescence. It also emphasizes the function of EOB2 in the adaptation of plants to specific guilds of pollinators

Identification of a second 16-hydroxytabersonine-O-methyltransferase suggests an evolutionary relationship between alkaloid and flavonoid metabolisms in Catharanthus roseus

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A cytosolic bifunctional geranyl/farnesyl diphosphate synthase provides MVA-derived GPP for geraniol biosynthesis in rose flowers

International audienceGeraniol derived from essential oils of various plant species is widely used in thecosmetic and perfume industries. It is also an essential trait of the pleasant smell ofrose flowers. In contrast to other monoterpenes which are produced in plastids via themethyl erythritol phosphate pathway, geraniol biosynthesis in roses relies on cytosolicNUDX1 hydrolase which dephosphorylates geranyl diphosphate (GPP). However,the metabolic origin of cytosolic GPP remains unknown. By feeding Rosa chinensis“Old Blush” flowers with pathway-specific precursors and inhibitors, combined withmetabolic profiling and functional characterization of enzymes in vitro and in planta,we show that geraniol is synthesized through the cytosolic mevalonate (MVA) path-way by a bifunctional geranyl/farnesyl diphosphate synthase, RcG/FPPS1, producingboth GPP and farnesyl diphosphate (FPP). The downregulation and overexpression ofRcG/FPPS1 in rose petals affected not only geraniol and germacrene D emissions butalso dihydro-β-ionol, the latter due to metabolic cross talk of RcG/FPPS1-dependentisoprenoid intermediates trafficking from the cytosol to plastids. Phylogenetic anal-ysis together with functional characterization of G/FPPS orthologs revealed thatthe G/FPPS activity is conserved among Rosaceae species. Site-directed mutagenesisand molecular dynamic simulations enabled to identify two conserved amino acidsthat evolved from ancestral FPPSs and contribute to GPP/FPP product specificity.Overall, this study elucidates the origin of the cytosolic GPP for NUDX1-dependentgeraniol production, provides insights into the emergence of the RcG/FPPS1 GPPSactivity from the ancestral FPPSs, and shows that RcG/FPPS1 plays a key role inthe biosynthesis of volatile terpenoid compounds in rose flowers

Alternative splicing creates a pseudo-strictosidine β- d -glucosidase modulating alkaloid synthesis in Catharanthus roseus

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