Perception and signalling of light and temperature cues in plants

Abstract

Light and temperature patterns are often correlated under natural plant growth conditions. In this review, we analyse the perception and signalling mechanisms shared by both these environmental cues and discuss the functional implications of their convergence to control plant growth. The first point of integration is the phytochrome B (phyB) receptor, which senses light and temperature. Downstream of phyB, the signalling core comprises two branches, one involving PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and the other CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and ELONGATED HYPOCOTYL 5 (HY5). The dynamics of accumulation and/or localization of each of these core signalling components depend on light and temperature conditions. These pathways are connected through COP1, which enhances the activity of PIF4. The circadian clock modulates this circuit, since EARLY FLOWERING 3 (ELF3), an essential component of the evening complex (EC), represses expression of the PIF4 gene and PIF4 transcriptional activity. Phytochromes are probably not the only entry point of temperature into this network, but other sensors remain to be established. The sharing of mechanisms of action for two distinct environmental cues is to some extent unexpected, as it renders these responses mutually dependent. There are nonetheless many ecological contexts in which such a mutual influence could be beneficial.

Local auxin production underlies a spatially restricted neighbor-detection response in Arabidopsis

“…PIF-controlled auxin biosynthesis is an essential step in shaderegulated hypocotyl and petiole elongation (11). Moreover, a role for auxin biosynthesis in shade-regulated leaf hyponasty was previously identified by analyzing the taa1/sav3 mutant (35).…”

“…In sunlight the R/FR is slightly above a value of 1, but, because of the strong absorbance of R and blue by photosynthetic pigments and the substantial reflection of FR by leaves, this ratio drops before actual shading and decreases further in true shade (3,10,11). Phytochromes (phy) sense the R/FR ratio, with phyB playing a predominant function in shade and neighbor detection (3).…”

“…Phytochromes (phy) sense the R/FR ratio, with phyB playing a predominant function in shade and neighbor detection (3). In sunlight a substantial fraction of phyB is active in preventing the SAS, while a reduction of the R/FR ratio gradually enhances elongation of hypocotyls, petioles, and stems (11). These growth responses are controlled by extensive transcriptional reprograming mediated primarily by three members of the phytochrome-interacting factor (PIF) family of basic helix-loop-helix (bHLH) transcription factors acting immediately downstream of phyB (12)(13)(14).…”

Phytochromes and Phytochrome Interacting Factors

“…Finally, we discuss the dynamic regulation of PIF DNA-binding and transcriptional activities through PIF-interacting partners. For details on the roles of phytochromes and PIFs in other pathways, readers are directed to recently published review articles (Legris et al, 2017;Paik et al, 2017).…”

Seedling Establishment: A Dimmer Switch-Regulated Process between Dark and Light Signaling

“…Finally, we discuss some of the challenges faced by young seedlings during their establishment, such as variations in temperature or in light quality and quantity. Although mentioned briefly, we do not cover in detail the contribution of sugars or temperature to seedling establishment in response to dark and light signals; we refer readers to excellent recent reviews Legris et al, 2017;Seluzicki et al, 2017). The emerging view is that of seedling establishment regulated as a dimmer-type switch where relative amounts of dark and light signaling dynamically optimize plant development to the surrounding light environment.…”