Light regulation of gibberellin biosynthesis in pea is mediated through the COP1/HY5 pathway - PubMed (original) (raw)
Light regulation of gibberellin biosynthesis in pea is mediated through the COP1/HY5 pathway
James L Weller et al. Plant Cell. 2009 Mar.
Abstract
Light regulation of gibberellin (GA) biosynthesis occurs in several species, but the signaling pathway through which this occurs has not been clearly established. We have isolated a new pea (Pisum sativum) mutant, long1, with a light-dependent elongated phenotype that is particularly pronounced in the epicotyl and first internode. The long1 mutation impairs signaling from phytochrome and cryptochrome photoreceptors and interacts genetically with a mutation in LIP1, the pea ortholog of Arabidopsis thaliana COP1. Mutant long1 seedlings show a dramatic impairment in the light regulation of active GA levels and the expression of several GA biosynthetic genes, most notably the GA catabolism gene GA2ox2. The long1 mutant carries a nonsense mutation in a gene orthologous to the ASTRAY gene from Lotus japonicus, a divergent ortholog of the Arabidopsis bZIP transcription factor gene HY5. Our results show that LONG1 has a central role in mediating the effects of light on GA biosynthesis in pea and demonstrate the importance of this regulation for appropriate photomorphogenic development. By contrast, LONG1 has no effect on GA responsiveness, implying that interactions between LONG1 and GA signaling are not a significant component of the molecular framework for light-GA interactions in pea.
Figures
Figure 1.
Shoot Phenotypes of long1, a New Elongated Pea Mutant. (A), (B), and (E) Phenotypes of elongated mutant seedlings under glasshouse conditions. Appearance of representative seedlings (A), internode lengths (B), and stem chlorophyll (chl) content (D). (C) and (E) Photoperiod response of wild-type and long1 mutant plants for node of flower initiation (E) and stem length between nodes 1 and 3 (C). All plants received an 8-h photoperiod of natural daylight either with (LD) or without (SD) a 16-h extension with low-irradiance cool-white fluorescent light. Values represent mean ±
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for n = 8 plants except for (D), where n = 4.
Figure 2.
LONG1 Functions in Phytochrome and Crytochrome Signaling. (A) Internode elongation of wild-type and long1 seedlings grown from sowing in darkness (D) or under continuous irradiation with far-red (FR), red (R), or blue (B) light (15 μmol m−2s−1) or white light (100 μmol m−2s−1) (B) Internode elongation and leaflet area of long1 mutant seedlings in different photoreceptor-deficient genetic backgrounds under continuous red (R) or blue (B) light (15 μmol m−2s−1). Values represent mean ±
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for n = 8 to 10 plants.
Figure 3.
The long1 Mutation Is Epistatic to lip1. (A) and (B) Interaction of long1 and lip1 in control of development in plants grown under continuous white light. (A) Appearance of representative seedlings. (B) Stem length between nodes 1 and 3 (n = 8 to 10) and chlorophyll content of internode 1 (n = 4 plants). Bars represent
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. (C) and (D) Interaction of long1 and lip1 in control of development in plants grown in continuous darkness. (C) Appearance of representative seedlings. (D) Stem length between nodes 1 and 3, and leaflet area (n = 8 to 10). Bars represent
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.
Figure 4.
LONG1 Is a Divergent Ortholog of Arabidopsis HY5. (A) Phylogenetic analysis of _HY5_-related genes. Deduced amino acid sequences were aligned and _HY5_-homologous regions (amino acids 77 to 151 in _At_HY5) were used to construct a neighbor-joining tree, shown with a root between HY5 and HYH clades. Bootstrap values were determined from 1000 replications and given above each branch as a percentage. The alignment is shown in Supplemental Figure 1 online. (B) Structure of the LONG1 gene and comparison with related Arabidopsis genes HY5 and CESA1. Boxes represent exons, and shaded regions within boxes represent coding sequence. The site of the long1-1 mutation is indicated.
Figure 5.
LONG1 Regulates Stem Elongation and GA Biosynthesis after Short-Term Transfer to Light. Two separate experiments were performed in which wild-type and _long1 s_eedlings ([A] to [D]) or wild-type, long1, lip1, and _long1 lip1s_eedlings ([E] and [F]) were grown in darkness (D) from sowing for 7 d before exposure to continuous white light (100 μmol m−2s−1) for four h (4 h W). (A) GA levels in expanding stem tissue of wild-type and _long1 s_eedlings. (B) Final stem length between nodes 1 and 3 of wild-type and _long1 s_eedlings. Measurements were taken at 14 d after sowing. Plants given the light treatment were returned to darkness for 7d following the treatment. (C) Levels of indole-3-acetic acid (IAA) in expanding stem tissue of wild-type and _long1 s_eedlings. (D) Relative transcript levels of GA biosynthesis genes GA3ox1 (LE), GA2ox1 (SLN), and GA2ox2 in expanding stem tissue of wild-type and _long1 s_eedlings. (E) GA levels in expanding stem tissue of wild-type, long1, lip1, and _long1 lip1s_eedlings. (F) Final stem length between nodes 1 and 3 of wild-type, long1, lip1, and long1 lip1 seedlings. Values represent mean ±
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for n = 3 biological replicates each consisting of material pooled from 8 to 10 plants, except (B) and (F), where n = 10 to 16 plants.
Figure 6.
Derepression of GA Biosynthesis in long1 Persists for Several Days after Transfer to Light. Wild-type and _long1 s_eedlings were grown in darkness (D) from sowing for 7 d before transfer to continuous white light (100 μmol m−2s−1). Tissue was harvested immediately before transfer to light and at 4, 8, 12, 24, 48, and 72 h after transfer. As an additional control, tissue was also harvested at the 72 h time point from plants maintained in continuous darkness. The two dark control points are connected by a dashed line. Values represent mean ±
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for n = 3. (A) Gibberellin A1 levels in expanding stem tissue. Values represent mean ±
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for n = 3 biological replicates each consisting of material pooled from 8 to 10 plants. (B) Relative transcript levels of GA biosynthesis genes LE (GA3ox1), SLN (GA2ox1), and GA2ox2 in expanding stem tissue. Values represent mean ±
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for n = 3 biological replicates each consisting of material pooled from three plants.
Figure 7.
Regulatory Interactions between LONG1 and GA Signaling. (A) Transcript levels of DELLA genes LA, CRY, and LONG1 in expanding stem tissue relative to those of ACTIN (ACT). Samples analyzed were the same as used in Figure 6B. Values represent mean ±
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for n = 3 biological replicates each consisting of material pooled from three plants. (B) Transcript levels of LONG1 in wild-type and la cry seedlings relative to those of ACT. Seedlings were grown in darkness (D) from sowing for 7 d before exposure to continuous white light (100 μmol m−2s−1) for 4 h (4 h W). Wild-type samples analyzed were the same as used in Figure 5D. Values represent mean ±
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for n = 3 biological replicates each consisting of material pooled from three plants. (C) Dose–response relationship for the effect of GA3 on internode elongation in light-grown wild-type and long1 seedlings. Varying amounts of GA3 were supplied together with a saturating dose of the GA biosynthesis inhibitor paclobutrazol (20 μg) in a 5-μL drop of ethanol applied to the exposed cotyledon surface of a dry seed. Control plants received ethanol only. Values represent mean ±
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for n = 10 to 16 plants. (D) Stem length between nodes 1 and 3 for wild-type, long1, la cry double mutant, and long1 la cry triple mutant seedlings grown under standard glasshouse conditions. Values represent mean ±
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for n = 6 to 8 plants. (E) Dose–response relationship for the effect of paclobutrazol on internode elongation in dark-grown wild-type and long1 seedlings. Varying amounts of paclobutrazol were applied in a 5-μL drop of ethanol to the exposed cotyledon surface of a dry seed. Control plants received ethanol only. Values represent mean ±
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for n = 10 to 16 plants.
Figure 8.
Interactions between Light and GA Pathways. (A) Physiologically and/or genetically distinct responses to light in pea identified in this study. Operators specify the direction but not the molecular nature of the interaction. (B) Model for interactions between light and GA pathways in dark- and light-grown seedlings. This diagram summarizes interactions identified from studies in Arabidopsis and pea. Genes and operators shown in black are active under the indicated light conditions; those shown in gray are inactive. The new interaction described in this study is shown as a dashed line. (C) Model for interactions between light and GA pathways in Arabidopsis seeds. Genes and operators shown in black are active; those shown in gray are inactive. Arrows represent activation; lines with flat ends represent inhibition.
References
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- Ang, L.H., Chattopadhyay, S., Wei, N., Oyama, T., Okada, K., Batschauer, A., and Deng, X.W. (1998). Molecular interaction between COP1 and HY5 defines a regulatory switch for light control of Arabidopsis development. Mol. Cell 1 213–222. -PubMed
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