Gibberellins Promote Flowering of Arabidopsis by Activating the LEAFY Promoter

Abstract

The gibberellin class of plant hormones has been implicated in the control of flowering in several species. In Arabidopsis, severe reduction of endogenous gibberellins delays flowering in long days and prevents flowering in short days. We have investigated how the differential effects of gibberellins on flowering correlate with expression of LEAFY , a floral meristem identity gene. We have found that the failure of gibberellin-deficient ga1-3 mutants to flower in short days was paralleled by the absence of LEAFY promoter induction. A causal connection between these two events was confirmed by the ability of a constitutively expressed LEAFY transgene to restore flowering to ga1-3 mutants in short days. In contrast to short days, impairment of gibberellin biosynthesis caused merely a reduction of LEAFY expression when plants were grown in long days or with sucrose in the dark. As a first step toward identifying other small molecules that might regulate flowering, we have developed a rapid in vitro assay for LEAFY promoter activity. INTRODUCTIONThe most dramatic phase change that flowering plants undergo is the transition from vegetative to reproductive growth. For this transition to be successful, plants must integrate a variety of environmental signals with endogenous cues, such as plant age (Bernier, 1988).In the facultative long-day plant Arabidopsis, the transition to reproductive growth occurs rapidly in long days but much more slowly in short days. Several flowering-time mutants, in which the timing of this transition is changed, have been isolated. Analysis of the responses of different mutants to the environment together with studies of their genetic interactions have resulted in a two-pathway model showing how the transition to flowering is regulated (Martínez-Zapater et al., 1994;Weigel, 1995;Peeters and Koornneef, 1996). According to this model, long days induce flowering via a facultative and fast pathway, whereas under noninductive photoperiods, an autonomous and much slower pathway is rate limiting. The latter pathway is thought to be related to plant age.The gibberellin (GA) class of plant hormones plays a role in many processes during plant development, including seed germination, cell elongation, and flowering (Finkelstein and Zeevaart, 1994). In Arabidopsis, physiological and genetic experiments have implicated GAs specifically in the autonomous pathway of flowering. Exogenous application of GAs accelerates flowering in wild-type Arabidopsis, particularly in short days (Langridge, 1957). That there is a causal connection between endogenous GA levels and flowering in Arabidopsis has been confirmed with several GA biosynthesis and signaling mutants. Mutants in which GA levels are severely reduced, such as ga1-3 , are unable to flower in short days (Wilson et al., 1992). ga1-3 mutants carry a deletion of the gene encoding ent -copalyl diphosphate synthase (formerly ent -kaurene synthetase A), which controls a key step in early GA biosynthesis (Koornneef and Van der Veen, 1980; Zeevaart and Talón, 19...

An ortholog of LEAFY in Jatropha curcas regulates flowering time and floral organ development

“…1E). Hence, JcLFY was not induced by GA in Jatropha , in contrast with Arabidopsis 3435 and Chrysanthemum 44.…”

“…For example, LFY controls auxin biosynthesis through repressing the auxin synthesis gene YUC4 ; in turn, auxin increases LFY transcription, and LFY promotes auxin signaling, leading to further increases in LFY activity33. In Arabidopsis , GA regulates LFY transcription to promote flower initiation343536. LFY represses the cytokinin signaling negative regulator ARR7 through a direct interaction with its promoter20.…”

pax1-1 partially suppresses gain-of-function mutations in Arabidopsis AXR3/IAA17

“…These include slow germination, short stature, dark green leaves (Figure 1a and 1b), protruding pistils (Figure 1g and 1h) and features indicative of slower phase change [44-47]. Plants pass through several distinct phases of development, marked by morphological changes in the lateral organs produced by the shoot apical meristem.…”

“…GA promotes germination and phase change, and increases stem and floral organ elongation [44-47]. pax1-1 plants show decreased germination, delayed phase change, reduced stem length, and altered floral organ elongation.…”

Proteomic and gene expression analyses during bolting-related leaf color change in Brassica rapa

“…Conversely, sucrose signal transduction regulates the expression of a large number of genes, and thereby influences a variety of important physiological and developmental processes. For example, sucrose has been found to directly regulate the expression of the flower regulator LFY (LEAFY) (Blazquez et al, 1998;Ohto et al, 2001) and is therefore important for regulating flowering in plants. In our study, we found that some large RuBisCO subunits were specifically expressed or upregulated after the leaf-color change.…”