Epigenetic modifiers regulate flowering time in Brassica crops

Flowering time is an important agronomic trait with a direct impact on crop yield. Plants control when to flower in response to a number of physiological and environmental cues. During the last decade, one focus of research has been on the regulatory pathways that regulate the floral repressor FLOWERING LOCUS C (FLC). The FLC gene is regulated by set of antagonistic molecular mechanisms including evolutionary conserved epigenetic regulators. For example, the methylation of FLC gene histones by Polcyomb is an epigenetic mark that silences gene expression. Eventually, the repressive epigenetic mark is erased by Jumonji histone demethylases activating FLC expression.

The epigenetic regulation of flowering time is a potential target for molecular breeding programs. However, most of what we know about plant epigenetics came from the study of the model plant Arabidopsis thaliana. The main goal of the EPIGENETIC REGULATION OF AGRONOMIC TRAITS group at CBGP is to translate the knowledge from Arabidopsis to its close Brassica crops relatives. The Brassica genus comprises a number of important vegetables such as turnip, cauliflower or broccoli, and oilseed crops like oilseed rape. Brassica vegetables are a key source of nutrients and vitamins for our diet and Brassica oilseed crops are a major source of edible oil worldwide.

Recently, researchers at CBGP studied the homologs of EARLY FLOWERING 6 (ELF6) and RELATIVE OF ELF6 (REF6), the main Arabidopsis histone demethylases, in a Brassica rapa oilseed crop. The authors performed genome-wide epigenomic and transcriptomic analyses that indicated that BraA.REF6 plays a greater role than BraA.ELF6 in fine-tuning epigenetic marks in the genome.

In addition, they found that braA.elf6 mutants were early flowering due low expression of the floral repressor FLC. However, unlike mutations in Arabidopsis, braA.ref6 mutants were late flowering without altering the expression of FLC. Finally, the researchers discovered that BraA.REF6 regulated a number of genes involved in the biosynthesis of gibberellins, plant hormones that regulate several developmental processes including flowering time.

This work increases our understanding of the epigenetic regulation of flowering time in Brassica crops highlighting conserved and distinct regulatory mechanisms between model and crop species. A full understanding of the epigenetic mechanisms regulating plant development is essential to exploit epigenetic variation in crop breeding programs and improve our agriculture. Since epigenetic mechanisms control fundamental processes that are common to plant and animal cells, the results of this work could also have an impact across other areas of life sciences.