Molecular mechanisms and ecological function of far‐red light signalling

Abstract

Land plants possess the ability to sense and respond to far-red light (700-760 nm), which serves as an important environmental cue. Due to the nature of far-red light, it is not absorbed by chlorophyll and thus is enriched in canopy shade and will also penetrate deeper into soil than other visible wavelengths. Far-red light responses include regulation of seed germination, suppression of hypocotyl growth, induction of flowering and accumulation of anthocyanins, which depend on one member of the phytochrome photoreceptor family, phytochrome A (phyA). Here, we review the current understanding of the underlying molecular mechanisms of how plants sense far-red light through phyA and the physiological responses to this light quality. Light-activated phytochromes act on two primary pathways within the nucleus; suppression of the E3 ubiquitin ligase complex CUL4/DDB1 and inactivation of the PHYTOCHROME INTERACTING FACTOR (PIF) family of bHLH transcription factors. These pathways integrate with other signal transduction pathways, including phytohormones, for tissue and developmental stage specific responses. Unlike other phytochromes that mediate red-light responses, phyA is transported from the cytoplasm to the nucleus in far-red light by the shuttle proteins FAR-RED ELONGATED HYPOCOTYL 1 (FHY1) and FHY1-LIKE (FHL). However, additional mechanisms must exist that shift the action of phyA to far-red light; current hypotheses are discussed.

RNA-seq Analysis of Meristem Cells Identifies the <i>FaFT3</i> Gene as a Common Floral Inducer in Japanese Cultivated Strawberry

“…PhyA is a phytochrome that primarily responds to red and far-red light, and FAR-RED-IMPAIRED RESPONSE1 (FAR1) is a transcription factor positively regulating the phyA-signaling pathway. PhyA exists in two photo-interconvertible forms termed Pr and Pfr, which absorb red light and far-red light, respectively (Sheerin and Hiltbrunner, 2017;Wang and Wang, 2015). Interestingly, illumination of the crowns of the cultivated strawberry 'Strawberry Festival' with red light resulted in a significant decrease in the number of flowering plants (Takeda et al, 2008).…”

Responses of Primula vulgaris to light quality in the maternal and germination environments

“…Plants possess several different photoreceptors to perceive light of specific wavelengths, from UV‐B to the near infrared (Kami et al . ; Sheerin & Hiltbrunner ). Among these, phytochromes respond to red (R) and far‐red (FR) light, which enables plants to detect vegetation using the R:FR ratio (Casal & Sánchez ).…”

Multiple Pathways in the Control of the Shade Avoidance Response

“…Attenuation of shade avoidance responses also involves Low R/FR stimulation of phyA signaling [9,40,41] ( Figure 2). The PHYA gene is early induced by Low R/FR, and phyA is required for the up-regulation of the basic leucine zipper (bZIP) transcription factor gene, ELONGATED HYPOCOTYL 5 (HY5), a central regulator of photomorphogenesis [42].…”

“…The COP1/SPA complexes are part of the CULLIN 4-DAMAGED DNA BINDING 1 ubiquitin E3 ligase complex (CUL4-DDB1 COP1/SPA ) and are required for substrate recognition [46]. Several positive regulators of photomorphogenesis, including HY5 and HFR1/SICS1, are targeted for 26 proteasome-mediated degradation by CUL4-DDB1 COP1/SPA [41]. The active form of phyA also interacts with COP1, and it has been recently proposed that binding of phyA to SPA proteins results in rearrangement of the interactions within the COP1/SPA complex rather than in its dissociation [45].…”

“…The active form of phyA also interacts with COP1, and it has been recently proposed that binding of phyA to SPA proteins results in rearrangement of the interactions within the COP1/SPA complex rather than in its dissociation [45]. Evidence exist that direct interaction of COP1 and SPA proteins is relevant for the activity of CUL4-DDB1 COP1/SPA , and it has been therefore proposed that binding of phyA to SPA proteins inactivates CUL4-DDB1 COP1/SPA which in turn results in the stabilization of positive regulators of photomorphogenesis [41] ( Figure 2). phyB in its active form has also been shown to bind to SPAs and inhibit their interaction with COP1 [45] ( Figure 2).…”