Abstract
It has been reported that Arabidopsis phytochrome (phy) A and phyB are crucial photoreceptors that display synergistic and antagonistic action during seedling de-etiolation in multiple light signaling pathways. However, the functional relationship between phyA and phyB is not fully understood under different kinds of light and in response to different intensities of such light. In this work, we compared hypocotyl elongation of the phyA-211 phyB-9 double mutant with the wild type, the phyA-211 and phyB-9 single mutants under different intensities of far-red (FR), red (R), blue (B) and white (W) light. We confirmed that phyA and phyB synergistically promote seedling de-etiolation in B-, B plus R-, W- and high R-light conditions. The correlation of endogenous ELONGATED HYPOCOTYL 5 (HY5) protein levels with the trend of hypocotyl elongation of all lines indicate that both phyA and phyB promote seedling photomorphogenesis in a synergistic manner in high-irradiance white light. Gene expression analyses of RBCS members and HY5 suggest that phyB and phyA act antagonistically on seedling development under FR light.
Highlights
Seedling photomorphogenesis is a classical model system for the study of light signal transduction in higher plants
The phyA-211 phyB-9 double mutant seedlings had even longer hypocotyls than the phyB-9 single mutant did, consistent with the phenotype of the phyA phyB double mutant in the Landsberg erecta (Ler) ecotype background [21]. These results indicate that there might be a synergistic effect between phyA and phyB, which explains the additional hypocotyl elongation of the phyA phyB
Less difference in hypocotyl length was observed between the phyB-9 mutant and the WT, the hypocotyl length of the phyA-211 phyB-9 double mutant was much longer than that of either the phyA-211 or phyB-9 mutant (Figure 2A,B). These results suggest that a mutual promotion between phyA and phyB may be responsible for the excessive hypocotyl elongation of the phyA-211 phyB-9 double mutant in response to B light
Summary
Seedling photomorphogenesis is a classical model system for the study of light signal transduction in higher plants. PhyA is mainly involved in response to FR light, such as inhibition of hypocotyl elongation, expansion of cotyledons and accumulation of anthocyanin [6,7,8]. Besides phyB, CRY1 has been identified as one of the major photoreceptors that are involved in inhibition of hypocotyl elongation and promotion of cotyledon expansion under white (W) light [12]. The germination defect caused by the phyA mutation in FR light can be suppressed by mutations in phyB [9,27,28]; antagonistic action of phyA and phyB has been found in seedling development and flowering [9]. We seek to illuminate the synergistic and antagonistic action between phyA and phyB during seedling photomorphogenesis in response to different kinds of light and light intensities
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