Gene-regulating mechanisms in early embryonic stage govern the flowering behavior of Arabidopsis

Researchers at GMI – Gregor Mendel Institute of Molecular Plant Biology of the Austrian Academy of Sciences – and the John Innes Center, Norwich, UK, determine that gene regulation mechanisms in early embryonic stage govern the flowering behavior of Arabidopsis later in development. The paper is published in the journal PNAS.

How do early life events shape the ability of organisms to respond to environmental signals later in life? Can such phenomena be explained at the mechanistic level? GMI chief and co-author Michael Nodine contradicts these questions with a clear statement: “Our research shows that gene regulation mechanisms established in early embryos prevent events that have serious physiological consequences long after they are initiated.”

What if spring could last longer?

Developmental phase transitions are controlled by precise quantitative regulation of gene expression. Decades of research on the Florida suppressor Arabidopsis FLC (Floral locus C), which is produced by default in a plant embryo after fertilization, has revealed the involvement of multiple molecular pathways that regulate its expression levels.

Ultimately, these pathways converge to fixed FLC expressions so that flowering only occurs in response to favorable environmental signals. In other words, the regulatory me mechanisms ensure that plants overwinter before flowering, a process called “vernalization,” as opposed to flowering several times a year (a fast cycle habit). However, the exact molecular interactions regulating FLC expression at specific developmental stages have remained poorly understood.

Decisions of early life have an effect “blooming” in adulthood

The team around GMI group leader Michael Nodine and Professor Dame Caroline Dean, group leader at the John Innes Center, Norwich, UK, investigated the antagonistic functions of the FLC activator FRIGIDA (FRI) and suppressor FCA (Flower Time Control Protein) at specific stages. of embryonic development of Arabidopsis.

The researchers, including first author Michael Schon and co-author Balaji Enugutti, a doctoral student and postdoctoral researcher in the Nodine group at GMI, respectively, raised the mysteries about the plant’s embryonic mechanisms that determine flowering behavior.

Namely, they found that FCA promotes the attachment of a poly-adenine (poly-A) tail close to the transcription starting site of the FLC mRNA, which produces the shorter and non-functional FLC protein. On the other hand, FRI promotes the attachment of the poly-A tail further downstream in the FLC mRNA, thus resulting in the longer and functional version of FLC.

In addition, the team found that the maximum antagonistic effect of FRI against FCA occurs at the early cardiac stage of embryonic development. FRI thus leads to increased FLC expression levels and, ultimately, ensures vernalization-dependent (delayed) flowering.

Setting the stage for flowering

With these findings, the researchers show that FLC transcription is antagonistically regulated in a transcriptional manner (because the mRNA is transcribed), and that these effects occur within early development in the plant embryo.

Additionally, they propose that the FLC antagonist FCA acts by establishing a specific chromatin state in the early embryonic developmental stages, which subsequently induces a rapid cyclic flowering habit without vernalization. On the other hand, this suppressed chromatin state is inhibited by the FLC activator FRI within the early cardiac stage, thus maintaining an FLC high transcription state that persists in later developmental stages and leads to wintering behavior.

Our findings demonstrate that opposite functions of co-transcriptional regulators at a very specific developmental stage have set the quantitative expression state of FLC. Understanding how gene regulatory mechanisms established early in life can influence processes that occur much later is of general interest in animals and plants. “

Michael Nodine, Group Leader, GMI – Gregor Mendel Institute of Molecular Plant Biology of the Austrian Academy of Sciences

Our findings will be of interest to researchers investigating RNA-mediated and epigenetic regulation of gene expression, as well as mechanisms governing evolutionary phase transitions including flowering time. “

Source:

GMI – Gregor Mendel Institute of Molecular Plant Biology of the Austrian Academy of Sciences

Reference journal reference:

Schon, M., et al. (2021) Antagonistic activities of co-transcription regulators within an early development window set an expression of FLC. PNAS. doi.org/10.1073/pnas.2102753118.

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