Phytochrome-Specific Type 5 Phosphatase Controls Light Signal Flux by Enhancing Phytochrome Stability and Affinity for a Signal Transducer

Abstract

Environmental light information such as quality, intensity, and duration in red (approximately 660 nm) and far-red (approximately 730 nm) wavelengths is perceived by phytochrome photoreceptors in plants, critically influencing almost all developmental strategies from germination to flowering. Phytochromes interconvert between red light-absorbing Pr and biologically functional far-red light-absorbing Pfr forms. To ensure optimal photoresponses in plants, the flux of light signal from Pfr-phytochromes should be tightly controlled. Phytochromes are phosphorylated at specific serine residues. We found that a type 5 protein phosphatase (PAPP5) specifically dephosphorylates biologically active Pfr-phytochromes and enhances phytochrome-mediated photoresponses. Depending on the specific serine residues dephosphorylated by PAPP5, phytochrome stability and affinity for a downstream signal transducer, NDPK2, were enhanced. Thus, phytochrome photoreceptors have developed an elaborate biochemical tuning mechanism for modulating the flux of light signal, employing variable phosphorylation states controlled by phosphorylation and PAPP5-mediated dephosphorylation as a mean to control phytochrome stability and affinity for downstream transducers.

Protein phosphatase 1 positively regulates stomatal opening in response to blue light in Vicia faba

“…However, the physiological roles of several members of the PPP family of protein phosphatases in plants have been recently identified by using Arabidopsis transgenic plants with loss-or gain-of-function mutants. For example, PP5 and PP6 have been demonstrated to modulate phytochrome-mediated signaling by dephosphorylating the Pfr form in the phosphorylated state (30,31). PP7 has been shown to act as a positive regulator in blue light signaling mediated by cryptochromes (32).…”

OWL1: An Arabidopsis J-Domain Protein Involved in Perception of Very Low Light Fluences

“…Furthermore, the phosphorylation state of phyA and therefore its activity and stability is light dependent (Lapko et al, 1997;Kim et al, 2004;Rubio and Deng, 2005;Trupkin et al, 2007). In addition, there is evidence that the phosphorylation state of the phyA dimer could lead to a preferential induction either of the FR-HIR or the VLFR pathway (Ryu et al, 2005;Trupkin et al, 2007;Kneissl et al, 2008).…”

Protein Phosphatase 2A B55 and A Regulatory Subunits Interact with Nitrate Reductase and Are Essential for Nitrate Reductase Activation

“…BSL1, 2, and 3 are expressed in leaves and older tissue (Mora-García et al, 2004), hence can be considered candidates for dephosphorylating NR. PP5 is known to promote expression of the light-regulated genes, CHALCONE SYNTHASE, CAB2, and RBCS (Ryu et al, 2005), and is a putative candidate for regulating also NR.…”