Light induced CHROMATIN DYNAMICS
CHROMATIN IS DYNAMICALLY REMODELED UNDER LIGHT CUESPlants only need soil, light and water to grow. This is what we learn, what we see every day. And indeed, land plants are heterotrophic because their leaves have this remarkable ability to capture and use sunlight to fuel a food-producing factory. Yet, at the beginning of its life, the young seedling growing through the dark soil cannot use light and relies on nutrients stored in its seed capsule, or own tissues, for several days. When the young plant emerges from the soil, the juvenile and naïve leaves are hit by light for the first time. Follows an extraordinary transformation in each cell of the leaf. Light is being captured, energy flows in the photosynthetic mill, the atmospheric carbon is being fixed and sugars, starch are being made. The seedling becomes self-sufficient, it becomes autotrophic. The young plant has undergone the juvenile-to-adult transition.
What operates this dramatic transformation? How does the plant reprogram its cellular machinery? The answer lays with a tiny, microscopic player in the cell. First identified as a colorable substance in the early XIX_th century, chromatin is a complex polymer that wraps the genetic material of eukaryotes and is encapsulated in the cell nucleus. Chromatin is also the programmable (molecular) hardware of the cell. Within minutes, hours, the chromatin twists, remodels, reassembles, redistributes instructions on the genes. In doing so, it establishes a new set of instructions for adapting the juvenile leaf to light. |
Chromatin is the molecular hardware of the cell, encapsulated in the nucleus. When seedlings are exposed to light for the first time, the chromatin of the embryonic leaf cells undergoes a dramatic reorganisation which coincides with an extensive reprogramming of transcription. Chromatin dynamics includes heterochromatin condensation seen in DAPI staining (gray), pericentromeric probing (red) and DNA methylation staining (green) (Bourbousse et al, PNAS 2015). One of the consequence is a drastic change in chromatin mobility (measured in fluorescence recovery analyses, graph) (Baroux & Barneche, unpublished).
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