ABSTRACT
Plants exhibit an enormous phenotypic plasticity to adjust to changing environmental conditions. For this purpose, they have evolved mechanisms to detect and measure biotic and abiotic factors in their surroundings. Phytochrome B exhibits a dual function, since it serves as a photoreceptor for red and far-red light as well as a thermosensor. In 1999, it was first reported that phytochromes not only translocate into the nucleus but also form subnuclear foci upon irradiation by red light. It took more than 10 years until these phytochrome speckles received their name; these foci were coined photobodies to describe unique phytochrome-containing subnuclear domains that are regulated by light. Since their initial discovery, there has been much speculation about the significance and function of photobodies. Their presumed roles range from pure experimental artifacts to waste deposits or signaling hubs. In this review, we summarize the newest findings about the meaning of phyB photobodies for light and temperature signaling. Recent studies have established that phyB photobodies are formed by liquid-liquid phase separation via multivalent interactions and that they provide diverse functions as biochemical hotspots to regulate gene expression on multiple levels.
Subject(s)
Phytochrome B , Phytochrome B/metabolism , Phytochrome B/genetics , Light , Signal Transduction , TemperatureABSTRACT
The size of plant organs is highly responsive to environmental conditions. The plant's embryonic stem, or hypocotyl, displays phenotypic plasticity, in response to light and temperature. The hypocotyl of shade avoiding species elongates to outcompete neighboring plants and secure access to sunlight. Similar elongation occurs in high temperature. However, it is poorly understood how environmental light and temperature cues interact to effect plant growth. We found that shade combined with warm temperature produces a synergistic hypocotyl growth response that dependent on PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) and auxin. This unique but agriculturally relevant scenario was almost totally independent on PIF4 activity. We show that warm temperature is sufficient to promote PIF7 DNA binding but not transcriptional activation and we demonstrate that additional, unknown factor/s must be working downstream of the phyB-PIF-auxin module. Our findings will improve the predictions of how plants will respond to increased ambient temperatures when grown at high density.
Subject(s)
Arabidopsis Proteins , Arabidopsis , Phytochrome , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Basic Helix-Loop-Helix Transcription Factors/genetics , Basic Helix-Loop-Helix Transcription Factors/metabolism , DNA-Binding Proteins/metabolism , Factor VII/genetics , Factor VII/metabolism , Gene Expression Regulation, Plant , Hypocotyl/metabolism , Indoleacetic Acids/metabolism , Light , Phytochrome/metabolismABSTRACT
Gibberellic acid (GA) promotes a range of developmental and growth processes in plants, the most well-known being germination, elongation growth and flowering time. DELLA repressors are the key players of the pathway. Their presence or their GA-dependent turnover via the 26S proteasome correlates to a large extent with the repression or derepression, respectively, of GA-dependent growth responses. Recent progress has revealed the role of DELLA repressors in several novel response pathways, and at the biochemical level, they have now been shown to function as repressors of the PHYTOCHROME INTERACTING FACTOR3 (PIF3) and PIF4 transcriptional activators in the context of light-regulated seedling development. Furthermore, the first insights have been gained into the evolution of the GA signalling pathway on the basis of comparative genomics between the moss Physcomitrella patens, the lycophyte Selaginella moellendorffii and seed plants.
