Light is one of the key environmental signals that influences plant growth and development. Plants utilize a wide range of sensory systems to perceive and transduce specific incoming environmental signals. Phytochromes are targeted by COP1 for degradation via the ubiquitin/26S proteasome pathway.Īs sessile organisms, plants have acquired a high degree of developmental plasticity to optimize their growth and reproduction in response to their ambient environment, such as light, temperature, humidity, and salinity. Photoactivated phytochromes rapidly change the expression of light-responsive genes by repressing the activity of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), an E3 ubiquitin ligase targeting several photomorphogenesis-promoting transcription factors for degradation, and by inducing rapid phosphorylation and degradation of Phytochrome-Interacting Factors (PIFs), a group of bHLH transcription factors repressing photomorphogenesis. Phytochromes are phosphoproteins, and can be dephosphorylated by a few protein phosphatases. Phytochromes may function as light-regulated serine/threonine kinases, and can phosphorylate several substrates, including themselves in vitro. phyB can enter the nucleus by itself in response to R light, whereas phyA nuclear import depends on two small plant-specific proteins FAR-RED ELONGATED HYPOCOTYL 1 (FHY1) and FHY1-LIKE (FHL). Upon light irradiation, phytochromes are converted to the biologically active Pfr form, and translocate into the nucleus. Phytochromes are synthesized in the cytosol in their inactive Pr form. phyA is light-labile and is the primary photoreceptor responsible for mediating photomorphogenic responses in FR light, whereas phyB-phyE are light stable, and phyB is the predominant phytochrome regulating de-etiolation responses in R light. There are five distinct phytochromes in Arabidopsis thaliana, designated phytochrome A (phyA) to phyE.

Phytochromes are red (R)/far-red (FR) light photoreceptors that play fundamental roles in photoperception of the light environment and the subsequent adaptation of plant growth and development.

Phytochrome full notes ppt