The amino‐terminus of phytochrome A contains two distinct functional domains

Abstract

The N-terminus of phytochrome A is important for the structural integrity and biological activity of the photoreceptor. Mutational analysis of the N-terminus by two different strategies created two distinct photoreceptors, one inactive and the other hyperactive when expressed in transgenic tobacco, suggesting that this region has multiple functional domains. To identify critical residues within this N-terminal region, a series of smaller deletions of oat phytochrome A were created, designated NB (delta49-62), NC (delta6-47), ND (delta7-21), NE (delta2-5), and NF (delta6-12), and compared with a previously characterized deletion mutant NA (delta7-69) and full-length oat phytochrome A. Using photochemical properties as a measure of chromoprotein structure, it was found that the region between residues 13 and 62 was important for the spectral integrity of the photoreceptor. These deletion mutants were also biologically inactive when expressed in both mature tobacco plants and seedlings grown under continuous far-red or red light. In contrast, deletion of the serine-rich region between residues 6 and 12 did not alter the photochemical properties but did produce a hyperactive photoreceptor, indicating this region may be involved in down-regulating phytochrome A activity. The data show that the N-terminus of phytochrome A contains two functional domains, one necessary for conformational stability and biological activity (residues 13-62), and the other involved in attenuating phytochrome responses (residues 6-12).

Light Control of Plant Development

“…This truncated form of phytochrome also has slightly blue-shifted absorption peaks and slower dark reversion rates. Mutation of the first 10 Ser of phyA to Ala (all contained within the first 20 aa) or deletion of this region results in a mutant that is hypersensitive to light (Stockhaus et al 1992, Jordan et al 1996. Previous results had shown that Pr phytochrome is phosphorylated at the N terminus (Wong et al 1986).…”

SPA1: A New Genetic Locus Involved in Phytochrome A–Specific Signal Transduction

“…Such a scenario was suggested as a function of the serine-rich region at the extreme N terminus of phyA. When a mutant monocot phyA construct having this region deleted or replaced by alanine residues was expressed in transgenic tobacco plants, it produced a hyperactive photoreceptor (Stockhaus et al, 1992;Emmler et al, 1995;Jordan et al, 1995). In an attempt to explain this phenotype, it was hypothesized that phosphorylation of these serine residues might reduce the signaling activity of wild-type phyA.…”

Missense Mutation in the Amino Terminus of Phytochrome A Disrupts the Nuclear Import of the Photoreceptor

“…The N-terminal extension domain (NTE; Neff et al, 2000) contains several Ser residues in phyA, which are subject to phosphorylation (Lapko et al, 1997(Lapko et al, , 1999. Experiments performed on modified phyA carrying Ser/Ala substitutions or deletions in the NTE proved that this region is necessary for correct intracellular localization, biological activity, and signal attenuation (Cherry et al, 1992;Stockhaus et al, 1992;Jordan et al, 1996Jordan et al, , 1997Casal et al, 2002;Trupkin et al, 2007).…”