Meta-analysis of transcriptomic studies of cytokinin-treated rice roots defines a core set of cytokinin response genes.

Cytokinins regulate diverse aspects of plant growth and development, primarily through modulation of gene expression. The cytokinin-responsive transcriptome has been thoroughly described in dicots, especially Arabidopsis, but much less so in monocots. Here, we present a meta-analysis of five different transcriptomic analyses of rice (Oryza sativa) roots treated with cytokinin, including three previously unpublished experiments.

Conserved bases for the initial cyclase in gibberellin biosynthesis: from bacteria to plants.

All land plants contain at least one class II diterpene cyclase (DTC), which utilize an acid-base catalytic mechanism, for the requisite production of -copalyl diphosphate (-CPP) in gibberellin A (GA) phytohormone biosynthesis. These -CPP synthases (CPSs) are hypothesized to be derived from ancient bacterial origins and, in turn, to have given rise to the frequently observed additional DTCs utilized in more specialized plant metabolism. However, such gene duplication and neo-functionalization has occurred repeatedly, reducing the utility of phylogenetic analyses.

Cytokinin modulates context-dependent chromatin accessibility through the type-B response regulators.

The phytohormone cytokinin regulates diverse aspects of plant growth and development, probably through context-dependent transcriptional regulation that relies on a dynamic interplay between regulatory proteins and chromatin. We employed the assay for transposase accessible chromatin with sequencing to profile changes in the chromatin landscape of Arabidopsis roots and shoots in response to cytokinin. Our results reveal differentially accessible chromatin regions indicative of dynamic regulation in response to cytokinin.

Catalytic Bases and Stereocontrol in Lamiaceae Class II Diterpene Cyclases.

Plants from the widespread Lamiaceae family produce many labdane-related diterpenoids, a number of which serve medicinal roles, and whose biosynthesis is initiated by class II diterpene cyclases (DTCs). These enzymes utilize a general acid-base catalyzed cyclo-isomerization reaction to produce various stereoisomers of the eponymous labdaenyl carbocation intermediate, which can then undergo rearrangement and/or the addition of water prior to terminating deprotonation. Identification of the pair of residues that cooperatively serve as the catalytic base in the DTCs that produce ent-copalyl diphosphate (CPP) required for gibberellin phytohormone biosynthesis in all vascular plants has led to insight into the addition of water as well as rearrangement.

Extreme promiscuity of a bacterial and a plant diterpene synthase enables combinatorial biosynthesis.

Diterpenes are widely distributed across many biological kingdoms, where they serve a diverse range of physiological functions, and some have significant industrial utility. Their biosynthesis involves class I diterpene synthases (DTSs), whose activity can be preceded by that of class II diterpene cyclases (DTCs). Here, a modular metabolic engineering system was used to examine the promiscuity of DTSs.

Product Rearrangement from Altering a Single Residue in the Rice syn-Copalyl Diphosphate Synthase.

Through site-directed mutagenesis targeted at identification of the catalytic base in the rice (Oryza sativa) syn-copalyl diphosphate synthase OsCPS4, changes to a single residue (H501) were found to induce rearrangement rather than immediate deprotonation of the initially formed bicycle, leading to production of the novel compound syn-halimadienyl diphosphate. These mutational results are combined with quantum chemical calculations to provide insight into the underlying reaction mechanism.

Blocking Deprotonation with Retention of Aromaticity in a Plant ent-Copalyl Diphosphate Synthase Leads to Product Rearrangement.

Substitution of a histidine, comprising part of the catalytic base group in the ent-copalyl diphosphate synthases found in all seed plants for gibberellin phytohormone metabolism, by a larger aromatic residue leads to rearrangements. Through a series of 1,2-hydride and methyl shifts of the initially formed bicycle predominant formation of (-)-kolavenyl diphosphate is observed. Further mutational analysis and quantum chemical calculations provide mechanistic insight into the basis for this profound effect on product outcome.