Lfall already. The length of the day is visibly shortened. The temperatures drop, seizing us with shivers in the early morning. We easily perceive these two indicators of seasonal rhythms, sunshine and temperature. Their annual variations are strongly correlated, light radiation being itself sources of heat; however, the experience of cold spells or out-of-season heat waves is there to remind us that light and ambient temperature can be dissociated.
When we change our behavior in the fall, turning on lights or a roaring fire, revamping our wardrobe or going to bed earlier, we’re not the only ones. Plants also perceive fluctuations in the physical parameters of their environment, depending on the season, time of day or the position of their neighbors, and they adjust their activity accordingly.
For this, molecular receptors detect variations in luminosity on the one hand, and in temperature on the other; different responses of the plant then engage, from the molecular scale to that of the organism. Among them, the expression of certain genes (for example, those involved in stem growth) is regulated according to light and heat.
Modulation of gene expression
In order for the receptors to efficiently transmit the instruction for a program change to the regulators of gene expression, there is nothing like grouping them together in a small space. This is what happens for phytochrome B, a photoreceptor of red and infrared light in many plants, which is also sensitive to temperature.
Under the effect of red light, this protein is activated and reaches the nucleus of plant cells. It forms clusters of about one micrometer in diameter, which are associated with the regulators of genes that respond to light variations. The high frequency of encounter between receptors and regulators within these structures favors the rapid and coordinated modulation of gene expression when phytochrome B picks up a signal.
Peking University researchers have studied the molecular properties of phytochrome B that govern its clustering or dispersion depending on light or thermal perception. Their results, published on August 18 in the journal Molecular Cell, reveal that, under the effect of red light, the photoreceptor molecules group together into liquid droplets which form a distinct phase from the rest of the nucleus, in the same way that oil droplets remain suspended in the aqueous phase of vinegar when emulsifying a vinaigrette. Conversely, droplets dissociate in the dark, under infrared light, or when the temperature increases from 15°C-20°C to 25°C-30°C.
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