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

Spirogyra filaments show unique photomovement which differs in response to blue, red and far-red light. Phototropins involved in the blue-light movement has been characterized together with downstream signaling components, but the photoreceptors and mechanical effectors of red- and far-red-light movement is not yet characterized. The filaments of S. varians slowly bent and aggregated to form a tangled mass in red light. In far-red light, the filaments unbent, stretched rapidly and separated from each other. Mannitol and/or sorbitol treatment significantly inhibited this far-red light movement suggesting that turgor pressure is the driving force of this movement. The bending and aggregating movement of filaments in red light were not affected by osmotic change. Three phytochrome homologues isolated from S. varians showed unique phylogenetic characteristics. Two canonical phytochromes, named SvPHY1 and SvPHY2, and a non-canonical phytochrome named SvPHYX2. SvPHY1 is the first PHY1 family phytochrome reported in zygnematalean algae. The gene involved in the transport of phytochromes into the nucleus was characterized, and its expression in response to red and far-red light was measured using quantitative PCR. Our results suggest that the phytochromes and the genes involved in the transport system into the nucleus are well conserved in S. varians. This article is protected by copyright. All rights reserved.