Out of the Dark and Into the Light: A New View of Phytochrome Photobodies

Abstract

Light is a critical environmental stimulus for plants, serving as an energy source via photosynthesis and a signal for developmental programming. Plants perceive light through various light-responsive proteins, termed photoreceptors. Phytochromes are red-light photoreceptors that are highly conserved across kingdoms. In the model plant Arabidopsis thaliana, phytochrome B serves as a light and thermal sensor, mediating physiological processes such as seedling germination and establishment, hypocotyl growth, chlorophyll biogenesis, and flowering. In response to red light, phytochromes convert to a biologically active form, translocating from the cytoplasm into the nucleus and further compartmentalizes into subnuclear compartments termed photobodies. PhyB photobodies regulate phytochrome-mediated signaling and physiological outputs. However, photobody function, composition, and biogenesis remain undefined since their discovery. Based on photobody cellular dynamics and the properties of internal components, photobodies have been suggested to undergo liquid-liquid phase separation, a process by which some membraneless compartments form. Here, we explore photobodies as environmental sensors, examine the role of their protein constituents, and outline the biophysical perspective that photobodies may be undergoing liquid-liquid phase separation. Understanding the molecular, cellular, and biophysical processes that shape how plants perceive light will help in engineering improved sunlight capture and fitness of important crops.

Signaling Mechanisms by Arabidopsis Cryptochromes

“…Interestingly, it was found that the recruitment of the MTA protein into CRY2 photobodies was blue light-dependent, raising the possibility that MTA concentrations locally increase in CRY2 photobodies under blue light without changing the affinity for interacting proteins ( Wang et al, 2021b ). Photobodies have been described as membrane-less compartments that concentrate molecules through liquid–liquid phase separation (LLPS; Pardi and Nusinow, 2021 ). During LLPS, two liquid phases are formed, a denser and a less dense one, thereby locally changing the concentration of biomolecules without the need for membranes.…”

Knocking Out the Transcription Factor OsNAC092 Promoted Rice Drought Tolerance

“…Our results also indicated that hormone-related gene expression of the IAA and ARF signaling pathways were significantly changed in our mutants ( Figure 5 ). Aquaporins PIP2-2 and PIP2-6 are important in the drought stress response, in which the ERAD component ubiquitin-conjugating enzyme UBC32 regulates drought tolerance positively in Arabidopsis thaliana by targeting PIP2-2 for degradation [ 47 ]. PIP2-2 and PIP2-6 were significantly differentially expressed in the osnac092 plants ( Figure 5 ).…”

Integration of light and temperature signaling pathways in plants

“…In the dark, phytochromes are synthesized in the cytosol in the Pr form; upon light irradiation, phytochromes are converted to the Pfr form and translocate into the nucleus, where they trigger light responses by modulating the expression of light‐responsive genes (Fankhauser and Chen, 2008; Klose et al, 2015). An outstanding feature of phytochrome signaling is the assembly of active phytochrome Pfr into discrete subnuclear foci, called nuclear bodies or photobodies, upon nuclear import of light‐activated phytochromes (Van Buskirk et al, 2012; Pardi and Nusinow, 2021). Although photobodies seem likely to be an essential cellular structure for phyB signaling, the precise function of photobodies in light signaling remains largely unknown (Chen et al, 2010; Van Buskirk et al, 2012; Pardi and Nusinow, 2021).…”

“…An outstanding feature of phytochrome signaling is the assembly of active phytochrome Pfr into discrete subnuclear foci, called nuclear bodies or photobodies, upon nuclear import of light‐activated phytochromes (Van Buskirk et al, 2012; Pardi and Nusinow, 2021). Although photobodies seem likely to be an essential cellular structure for phyB signaling, the precise function of photobodies in light signaling remains largely unknown (Chen et al, 2010; Van Buskirk et al, 2012; Pardi and Nusinow, 2021). A very recent study provided evidence showing that the CRY2 photobodies result from light‐induced liquid–liquid phase separation, and that photoexcited CRY2 recruits RNA‐modifying enzymes to these sites (Wang et al, 2021b).…”