PP7 Is a Positive Regulator of Blue Light Signaling in Arabidopsis

Abstract

The cryptochrome blue light photoreceptors mediate various photomorphogenic responses in plants, including hypocotyl elongation, cotyledon expansion, and control of flowering time. The molecular mechanism of cryptochrome function in Arabidopsis is becoming increasingly clear, with recent studies showing that both CRY1 and CRY2 are localized in the nucleus and that CRY2 is regulated by blue light-dependent phosphorylation. Despite these advances, no positive cryptochrome signaling component has been identified to date. Here, we demonstrate that a novel Ser/Thr protein phosphatase (AtPP7) with high sequence similarity to the Drosophila retinal degeneration C protein phosphatase acts as an intermediate in blue light signaling. Transgenic Arabidopsis seedlings with reduced AtPP7 expression levels exhibit loss of hypocotyl growth inhibition and display limited cotyledon expansion in response to blue light irradiation. These effects are as striking as those seen in hy4 mutant seedlings, which are deficient in CRY1. We further demonstrate that AtPP7 transcript levels are not rate limiting and that AtPP7 probably acts downstream of cryptochrome in the nucleus, ensuring signal flux through the pathway. Based on our findings and recent data regarding cryptochrome action, we propose that AtPP7 acts as a positive regulator of cryptochrome signaling in Arabidopsis.

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

“…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). In these analyses, Arabidopsis T-DNA insertional lines and antisense lines were excellent tools to dissect the role of individual enzymes because these catalytic subunits of protein phosphatases are encoded by one or two genes (33,34).…”

HYPERSENSITIVE TO RED AND BLUE 1, a ZZ-Type Zinc Finger Protein, Regulates Phytochrome B–Mediated Red and Cryptochrome-Mediated Blue Light Responses

“…SUB1, a cytoplasmic calcium binding protein, functions downstream of crys and negatively modulates phyAmediated far-red light responses. Recently, a positively acting component in blue light signaling, PP7, has been identified (Møller et al, 2003). The light signals are further modulated by proteosome-mediated degradation of HY5 and LAF1 through the constitutive repressors of photomorphogenesis or COP/DET/ FUS components (Osterlund et al, 2000;Seo et al, 2003).…”

Regulation of Apoptosis Signal-regulating Kinase 1 (ASK1) by PolyamineLevels via Protein Phosphatase5

“…PP5 has also been reported to associate with both isoforms of chryptochromes (blue light photoreceptors) and to be stimulated by at least one of them (22). Intriguingly, a distantly related plant PPP phosphatase PP7, which has no TPR domain but shares with PP5 a common atypical nuclear targeting signal (23), has recently been implicated in signaling downstream of cryptochromes (24). Because animal and plant chryptochromes are thought to have evolved from DNA photolyases independently (25), this may suggest convergent evolution not only of these photoreceptors but also of the signaling mechanisms they trigger.…”