Independent regulation of flowering by phytochrome B and gibberellins in Arabidopsis - PubMed (original) (raw)

Independent regulation of flowering by phytochrome B and gibberellins in Arabidopsis

M A Blázquez et al. Plant Physiol. 1999 Aug.

Abstract

Phytochromes and gibberellins (GAs) coordinately regulate multiple aspects of Arabidopsis development. Phytochrome B (PHYB) promotes seed germination by increasing GA biosynthesis, but inhibits hypocotyl elongation by decreasing the responsiveness to GAs. Later in the life cycle of the plant, PHYB and GAs have opposite effects on flowering. PHYB delays flowering, while GAs promote flowering, particularly under noninductive photoperiods. To learn how PHYB and GAs interact in the control of flowering, we have analyzed the effect of a phyB mutation on flowering time and on the expression of the floral meristem-identity gene LFY (LEAFY). We show that the early flowering caused by phyB correlated with an increase in LFY expression, which complements our previous finding that GAs are required for activation of LFY under noninductive photoperiods (M.A. Blázquez, R. Green, O. Nilsson, M.R. Sussman, D. Weigel [1998] Plant Cell 10: 791-800). Since phyB did not change the GA responsiveness of the LFY promoter and suppressed the lack of flowering of severe GA-deficient mutants under short days, we propose that PHYB modulates flowering time at least partially through a GA-independent pathway. Interestingly, the effects of PHYB on flowering do not seem to be mediated by transcriptional up-regulation of genes such as CO (CONSTANS) and FT (Flowering locus T), which are known to mediate the effects of the photoperiod-dependent floral-induction pathway.

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Figures

Figure 1

Figure 1

Light spectrum inside the growth chambers used in this work. The solid black line represents the spectrum provided by a 3:1 mixture of cool-white to fluorescent light, while the dotted line represents the spectrum provided by cool-white light alone.

Figure 2

Figure 2

LFY::GUS expression during vegetative growth of _phyB_-5 mutants. Plants homozygous for the LFY::GUS transgene either in a PHYB+ (DW150-304; white symbols) or _phyB_-5 background (307B5; black symbols) were grown in long days (squares) or short days (circles) until flower buds were visible to the naked eye. Values are expressed as means ± 2

se

(n = 12). Time represents days after sowing. Error bars that are not visible are contained within the symbol. MUG, 4-Methylumbelliferyl-β-

d

-glucopyranoside.

Figure 3

Figure 3

Suppression of the _ga1_-3 flowering defect in short days by _phyB_-5. Representative plants were photographed 50 d after sowing. Arrowhead indicates flowers.

Figure 4

Figure 4

LFY::GUS expression during vegetative growth of _ga1_-3 and _ga1_-_3 phyB_-5 mutants. Plants homozygous for the LFY::GUS transgene were grown in long (A) or short (B) days until flower buds were visible to the naked eye, except in the case of the _ga1_-3 mutant without GA3 treatment under short days (□), which had not flowered at the end of the experiment. 304G1 (_ga1_-3, white symbols) and 304G1B5 (_ga1_-_3 phyB_-5, black symbols) were treated with GA3 (circles) or left untreated (squares). Values are expressed as means ± 2

se

(n = 12). Time represents days after sowing. Error bars that are not visible are contained within the symbol. MUG, 4-Methylumbelliferyl-β-

d

-glucopyranoside.

Figure 5

Figure 5

Responses of _ga1_-3 and _ga1_-_3 phyB_-5 seedlings to exogenous GA3. Seeds of the lines 304G1 (_LFY::GUS ga1_-3, ○) and 304G1B5 (_LFY::GUS ga1_-_3 phyB_-5, •) were sown on MS plates containing the indicated concentrations of GA3. Hypocotyl length (A) and GUS activity (B) were determined 7 d after sowing. Values are expressed as means ± 2

se

(n = 12). Time represents days after sowing. Error bars that are not visible are contained within the symbol. MUG, 4-Methylumbelliferyl-β-

d

-glucopyranoside.

Figure 6

Figure 6

Responses of _ga1_-3 and _ga1_-_3 phyB_-5 seedlings to the GA-biosynthesis-inhibitor paclobutrazol. Seeds of the lines DW150-304 (LFY::GUS, ○) and 304B5 (_LFY::GUS phyB_-5, •) were sown on MS plates containing the indicated concentrations of paclobutrazol. Hypocotyl length (A) and GUS activity (B) were determined 7 d after sowing. Values are expressed as means ± 2

se

(n = 12). Time represents days after sowing. Error bars that are not visible are contained within the symbol. MUG, 4-Methylumbelliferyl-β-

d

-glucopyranoside.

Figure 7

Figure 7

CO and FT RNA expression in phyB mutants. Seedlings of the lines DW150-304 (wild type [WT], white bars) and 304B5 (_phyB_-5, black bars) were grown on MS plates under short days (SD), and harvested during the 8th h of light on the indicated days. Expression was analyzed by RT-PCR (bottom panel) and the signals quantified and normalized using UBQ expression as a control (top panel, arbitrary units).

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