Spatio-temporal regulation of arabidopsis flowering locus C

Reeck, Svenja Marie (2023) Spatio-temporal regulation of arabidopsis flowering locus C. Doctoral thesis, University of East Anglia.

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The regulation of gene expression of developmental genes is pivotal for an organism's lifecycle.
At the single-cell level, gene expression can occur through digital or analogue
mechanisms. In the digital mode, genes exhibit binary ON/OFF states, different fractions
of which generate the cell population average, while the analogue mode features graded
gene expression with varying transcriptional output at each gene copy. Both modes are
known to exist but how they are integrated to regulate one locus is unknown.

The floral repressor FLOWERING LOCUS C (FLC) in Arabidopsis exhibits digital Polycomb
silencing in response to prolonged cold, creating quantitative epigenetic memory.
However, how quantitatively different FLC levels are achieved independent of cold
exposure remains elusive. To investigate this, an allelic series of mutations in FCA, a key
regulatory player in the cold-independent autonomous pathway of FLC regulation, was
used to perform quantitative fluorescent imaging. A dual regulation mechanism for FLC is
observed, with analogue preceding digital regulation. Intermediate analogue FLC levels
facilitated gradual digital silencing at the population level, as more cells switched OFF over
time. Live imaging during embryo development showed that cells are initially ON,
followed by an analogue and digital response post-germination. The digital response
depends on the previously set-up analogue transcription level and is mediated by the
Polycomb Repressive Complex 2.

Fluctuating winter-like temperatures, including a below-freezing period, induced the
upregulation of FLC antisense transcripts, collectively named COOLAIR. Using
Fluorescence in situ hybridization, I show that the upregulation can be accounted for by an
increased number of cells expressing COOLAIR and more COOLAIR transcripts
accumulating in a defined focus at active transcription sites. In a spatial context, specific
meristematic cells were identified as enriched with COOLAIR.

These findings show the interplay between analogue transcriptional and digital epigenetic
pathways to set up transcriptional levels. The importance of elucidating the mechanism at
play to achieve the correct timing of developmentally important genes is highlighted, which
could include the role of antisense transcription in fine-tuning the response in specific cells
when exposed to freezing temperatures.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Zoe White
Date Deposited: 09 Jul 2024 15:04
Last Modified: 09 Jul 2024 15:04


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