Abstract
BackgroundPhyC levels have been observed to be markedly lower in phyB mutants than in Arabidopsis or rice wild type etiolated seedlings, but the mechanism of this phenomenon has not been fully elucidated.ResultsIn the present study, we investigated the mechanism by which phyB affects the protein concentration and photo-sensing abilities of phyC and demonstrated that rice phyC exists predominantly as phyB/phyC heterodimers in etiolated seedlings. PHYC-GFP protein was detected when expressed in phyA phyC mutants, but not in phyA phyB mutants, suggesting that phyC requires phyB for its photo-sensing abilities. Interestingly, when a mutant PHYB gene that has no chromophore binding site, PHYB(C364A), was introduced into phyB mutants, the phyC level was restored. Moreover, when PHYB(C364A) was introduced into phyA phyB mutants, the seedlings exhibited de-etiolation under both far-red light (FR) and red light (R) conditions, while the phyA phyB mutants were blind to both FR and R. These results are the first direct evidence that phyC is responsible for regulating seedling de-etiolation under both FR and R. These findings also suggest that phyB is indispensable for the expression and function of phyC, which depends on the formation of phyB/phyC heterodimers.SignificanceThe present report clearly demonstrates the similarities and differences in the properties of phyC between Arabidopsis and rice and will advance our understanding of phytochrome functions in monocots and dicots.
Highlights
Plants sense diverse light signals from the environment via a family of plant photoreceptors, including phytochromes, cryptochromes, and phototropins
To analyze the interaction between phyB and phyC, we initially quantified the relative levels of phyB and phyC in wild type (WT) rice seedlings grown under either continuous darkness or continuous white light (cW) by comparative western blotting by using purified proteins as standards (Fig. S1)
Protein extracts from 5-day-old etiolated seedlings and dilution series of standard proteins (PHYB-His or PHYC-His) were separated by SDS-PAGE on the same gel, and phyB and phyC were detected by anti-PHYB and anti-PHYC antibodies, respectively
Summary
Plants sense diverse light signals from the environment via a family of plant photoreceptors, including phytochromes, cryptochromes, and phototropins. Phytochromes are chromoproteins that regulate the expression of a large number of light-responsive genes and influence many photomorphogenic events [1,2,3,4,5]. Phytochromes in higher plants are encoded by small gene families [7,8]. Molecular phylogenetic analyses indicate that the angiosperm phytochrome gene family is composed of four subfamilies, PHYTOCHROME A (PHYA), PHYB, PHYC/F, and PHYE [9]. In Arabidopsis, PHYD is further derived from an ancestral PHYB gene by a recent gene duplication event [7], and as a result, Arabidopsis has five PHY genes, PHYA to PHYE [7,10]. PhyC levels have been observed to be markedly lower in phyB mutants than in Arabidopsis or rice wild type etiolated seedlings, but the mechanism of this phenomenon has not been fully elucidated
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