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Summary: The biosynthesis of specialized metabolites is strictly regulated by environmental inputs such as the day–night cycle, but the underlying mechanisms remain elusive. In Petunia hybrida cv. Mitchell flowers, the biosynthesis and emission of volatile compounds display a diurnal pattern with a peak in the evening to attract nocturnal pollinators.Using petunia flowers as a model system, we found that chromatin level regulation, especially histone acetylation, plays an essential role in mediating the day–night oscillation of the biosynthetic gene network of specialized metabolites.By performing time‐course chromatin immunoprecipitation assays for histone modifications, we uncovered that a specific group of genes involved in the regulation, biosynthesis, and emission of floral volatile compounds, which displays the greatest magnitude in day–night oscillating gene expression, is associated with highly dynamic histone acetylation marks H3K9ac and H3K27ac. Specifically, the strongest oscillating genes featured a drastic removal of histone acetylation marks at night, potentially to shut down the biosynthesis of floral volatile compounds during the morning when they are not needed. Inhibiting daytime histone acetylation led to a compromised evening induction of these genes.Overall, our study suggested an active role of chromatin modification in the diurnal oscillation of specialized metabolic network. [ABSTRACT FROM AUTHOR]

SUMMARY: Scent bouquets produced by the flowers of Petunia spp. (petunia) are composed of a complex mixture of floral volatile benzenoid and phenylpropanoid compounds (FVBPs), which are specialized metabolites derived from phenylalanine (Phe) through an interconnected network of enzymes. The biosynthesis and emission of high levels of these volatiles requires coordinated transcriptional activation of both primary and specialized metabolic networks. The petunia R2R3‐MYB transcription factor ODORANT 1 (ODO1) was identified as a master regulator of FVBP production and emission; however, our knowledge of the direct regulatory targets of ODO1 has remained limited. Using chromatin immunoprecipitation followed by sequencing (ChIP‐seq) in petunia flowers, we identify genome‐wide ODO1‐bound genes that are enriched not only in genes involved in the biosynthesis of the Phe precursor, as previously reported, but also genes associated with the specialized metabolic pathways involved in generating phenylpropanoid intermediates for FVBPs. ODO1‐bound genes are also involved in methionine and S‐adenosylmethionine metabolism, which could modulate methyl group supplies for certain FVBPs. Quantitative reverse transcription polymerase chain reaction (qRT‐PCR) and RNA‐seq analysis in an ODO1 RNAi knockdown line revealed that ODO1‐bound targets are expressed at lower levels when ODO1 is suppressed. A cis‐regulatory motif, CACCAACCCC, was identified as a potential binding site for ODO1 in the promoters of genes that are both bound and activated by ODO1, which was validated by in planta promoter reporter assays with wild‐type and mutated promoters. Overall, our work presents a mechanistic model for ODO1 controlling an extensive gene regulatory network that contributes to FVBP production to give rise to floral scent. Significance Statement: Petunia floral scent production and emission is highly regulated, with a major role for the transcription factor ODORANT 1 (ODO1). This paper describes the ODO1‐regulated gene network of petunia, which extends to branches involved in the production of phenylpropanoid intermediates and S‐adenosylmethionine biosynthesis, along with the identification of an ODO1‐binding motif. [ABSTRACT FROM AUTHOR]

Chromatin modification has gained increased attention for its role in the regulation of plant responses to environmental changes, but the specific mechanisms and molecular players remain elusive. Here, we show that the Arabidopsis ( Arabidopsis thaliana ) histone methyltransferase SET DOMAIN GROUP8 (SDG8) mediates genome-wide changes in H3K36 methylation at specific genomic loci functionally relevant to nitrate treatments. Moreover, we show that the specific H3K36 methyltransferase encoded by SDG8 is required for canonical RNA processing, and that RNA isoform switching is more prominent in the sdg8-5 deletion mutant than in the wild type. To demonstrate that SDG8-mediated regulation of RNA isoform expression is functionally relevant, we examined a putative regulatory gene, CONSTANS , CO-like , and TOC1 101 ( CCT101 ), whose nitrogen-responsive isoform-specific RNA expression is mediated by SDG8. We show by functional expression in shoot cells that the different RNA isoforms of CCT101 encode distinct regulatory proteins with different effects on genome-wide transcription. We conclude that SDG8 is involved in plant responses to environmental nitrogen supply, affecting multiple gene regulatory processes including genome-wide histone modification, transcriptional regulation, and RNA processing, and thereby mediating developmental and metabolic processes related to nitrogen use., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

The use of fluorescent proteins fused to other proteins has been very useful in revealing the location and function of many proteins. However, it is very important to show that the fusion of these reporter proteins does not impact the function of the protein of interest. Plants have 2 forms of the cap-binding protein that function in initiation of translation, eIF4E and a plant specific form, eIFiso4E. In an attempt to determine the cellular localization of eIFiso4E, fusions to GFP were made, but were found to not be competent to rescue the lethal phenotype of plants lacking eIF4E and eIFiso4E. This suggested that the GFP fusions at either the N- or C-terminus of eIFiso4E were not functional. Biochemical analysis of the fusions revealed that eIFiso4E•GFP fusions were not able to bind to m 7 GTP Sepharose indicating that they were not functional as cap-binding proteins. Analysis of eIF4E•GFP fusions, both in yeast and in vitro , showed that the N-terminal fusion may be functional, whereas the C-terminal fusion bound m 7 GTP Sepharose very poorly and functioned poorly in yeast. These results highlight the importance of verification both biochemically and in vivo that reporter fusions of proteins maintain activity and are stable in order to prevent observations that may result in artifacts.