Holophytochrome-Interacting Proteins in Physcomitrella: Putative Actors in Phytochrome Cytoplasmic Signaling

Abstract

Phytochromes are the principle photoreceptors in light-regulated plant development, primarily acting via translocation of the light-activated photoreceptor into the nucleus and subsequent gene regulation. However, several independent lines of evidence indicate unambiguously that an additional cytoplasmic signaling mechanism must exist. Directional responses in filament tip cells of the moss Physcomitrella patens are steered by phy4 which has been shown to interact physically with the blue light receptor phototropin at the plasma membrane. This complex might perceive and transduce vectorial information leading to cytoskeleton reorganization and finally a directional growth response. We developed yeast two-hybrid procedures using photochemically functional, full-length phy4 as bait in Physcomitrella cDNA library screens and growth assays under different light conditions, revealing Pfr-dependent interactions possibly associated with phytochrome cytoplasmic signaling. Candidate proteins were then expressed in planta with fluorescent protein tags to determine their intracellular localization in darkness and red light. Of 14 candidates, 12 were confirmed to interact with phy4 in planta using bimolecular fluorescence complementation. We also used database information to study their expression patterns relative to those of phy4. We discuss the likely functional characteristics of these holophytochrome-interacting proteins (HIP’s) and their possible roles in signaling.

Red And far‐red regulation of filament movement correlates with the expression of phytochrome and FHY1 genes in Spirogyra varians (Zygnematales, Streptophyta)1

“…Phytochrome is known to signal physiological responses in diverse stages of plant morphogenesis and often activates several regulation pathways at a time (Hughes 2013). The mechanism of phytochrome action is still only partly understood despite the intensive study (Ermert et al 2016). Our results showed that S. varians can provide a unique experimental system to study red-/far-red light signaling, and its interaction with blue-light signaling as well as the coordination of their mechanical effectors at a cellular level.…”

“…The mechanism of phytochrome action is still only partly understood despite the intensive study (Ermert et al. ). Our results showed that S. varians can provide a unique experimental system to study red‐/far‐red light signaling, and its interaction with blue‐light signaling as well as the coordination of their mechanical effectors at a cellular level.…”

“…Despite intensive study worldwide for more than half a century, the mechanism of phytochrome action is still only partly understood, and very little is known about its cytoplasmic regulation (Ermert et al. ).…”

“…Phytochrome can regulate transcription after being transported into the nucleus (Li et al 2010, Leivar and Quail 2011, Wang and Wang 2015, or directly regulate translation of mRNA in the cytosol (Paik et al 2012). Despite intensive study worldwide for more than half a century, the mechanism of phytochrome action is still only partly understood, and very little is known about its cytoplasmic regulation (Ermert et al 2016).…”

Phytochrome diversification in cyanobacteria and eukaryotic algae

“…In streptophyte algae and some nonvascular plants, neochromes function in the cytosol to mediate changes in plastid orientation and/or directional growth in response to light [48]. Higher plant phytochromes function in both the cytosol and the nucleus, with candidate interacting proteins identified in both compartments [49]. Light-dependent nuclear import of plant phytochromes is a critical step in inducing photomorphogenesis [50].…”