Phytochrome Kinase Substrate 4 is phosphorylated by the phototropin 1 photoreceptor.
Phototropism allows plants to redirect their growth towards the light to optimize photosynthesis under reduced light conditions. Phototropin 1 (phot1) is the primary low blue light-sensing receptor triggering phototropism in Arabidopsis. Light-induced autophosphorylation of phot1, an AGC-class protein kinase, constitutes an essential step for phototropism. However, apart from the receptor itself, substrates of phot1 kinase activity are less clearly established. Phototropism is also influenced by the cryptochromes and phytochromes photoreceptors that do not provide directional information but influence the process through incompletely characterized mechanisms. Here, we show that Phytochrome Kinase Substrate 4 (PKS4), a known element of phot1 signalling, is a substrate of phot1 kinase activity in vitro that is phosphorylated in a phot1-dependent manner in vivo. PKS4 phosphorylation is transient and regulated by a type 2-protein phosphatase. Moreover, phytochromes repress the accumulation of the light-induced phosphorylated form of PKS4 showing a convergence of photoreceptor activity on this signalling element. Our physiological analyses suggest that PKS4 phosphorylation is not essential for phototropism but is part of a negative feedback mechanism.
Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.
Emilie
E
Demarsy
Isabelle
I
Schepens
Koji
K
Okajima
Micha
M
Hersch
Sven
S
Bergmann
John
J
Christie
Ken-Ichiro
K
Shimazaki
Satoru
S
Tokutomi
Christian
C
Fankhauser
D017360:Arabidopsis / Q000201:enzymology / Q000502:physiology; D029681:Arabidopsis Proteins / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D052817:Phototrophic Processes; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; C103646:NPH1 protein, Arabidopsis; C512593:PKS4 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases