A possible tyrosine phosphorylation of phytochrome

Abstract

Red/far-red light signal transduetion by the phytochrome family of photoreceptors regulates plant growth and development. We investigated the possibility that tyrosine kinases and/or phosphatases are involved in phytochromemediated signal transduction using crude extracts of oat seedlings that are grown in the dark. We found that a 124 kDa protein was tyrosine-phosphorylated as determined by Western blotting with a phosphotyrosine-specific monoclonal antibody. The 124 kDa protein was recognized by the anti-phosphotyrosine antibody in anti-phytochrome A immunoprecipitates. The level of anti-phosphotyrosinc antibody binding to the 124 kDa protein(s) in phytochrome immunoprecipitates that had been treated with red light prior to immunoprecipitation decreased relative to dark controls. These results suggest that either phytochrome from dark-grown seedlings is tyrosine phosphorylated or that it coimmunoprecipitates with a phosphotyrosine-containing protein of the same molecular weight. The implications of these results in the regulation of (a) the putative Ser/Thr kinase activity of the photoreceptor and (b) the binding of signaling molecules, such as phospholipase C to phytochrome, are discussed.

Tyrosine Phosphorylation Regulates the Activity of Phytochrome Photoreceptors

“…A few early studies implicated phosphotyrosines in pathogen and light response, and developmental pathways (Barizza et al, 1999; Kameyama et al, 2000; Sommer et al, 1996; Suzuki and Shinshi, 1995; Tong et al, 1996), but follow-up studies have been lacking. In addition to the early reports, a proteomics study identified a large-scale phosphorylation map in Arabidopsis .…”

Elementary Processes of Photoperception by Phytochrome A for High-Irradiance Response of Hypocotyl Elongation in Arabidopsis,

“…Autophosphorylation of cyanobacterial phytochrome was promoted by continuous FR irradiation (when Pr should predominate) rather than by continuous R irradiation (when Pfr should predominate) (Yeh et al, 1997). In oat phytochrome, Pfr (Sommer et al, 1996) and also Pr (Yeh and Lagarias, 1998) were phosphorylated. The phytochrome action model (Yeh and Lagarias, 1998) based upon those molecular data is consistent with the idea from the present physiological study that photoconversion of PhyA into Pr by FR light perception promotes a biologically active signal.…”

Maize protein phosphatase gene family: identification and molecular characterization

“…In particular, the level of tyrosine phosphorylation is determined by the balanced activity of protein tyrosine kinases (PTKs) and PTPs. Moreover, previous study showed that tyrosine phosphorylation is involved in phytohormone responses [16]. Compared with plants, other genomes which lack tyrosine kinases also have very few PTPs.…”