SHORT VEGETATIVE PHASE reduces gibberellin biosynthesis at the Arabidopsis shoot apex to regulate the floral transition

Abstract

In Arabidopsis thaliana environmental and endogenous cues promote flowering by activating expression of a small number of integrator genes. The MADS box transcription factor SHORT VEG-ETATIVE PHASE (SVP) is a critical inhibitor of flowering that directly represses transcription of these genes. However, we show by genetic analysis that the effect of SVP cannot be fully explained by repressing known floral integrator genes. To identify additional SVP functions, we analyzed genome-wide transcriptome data and show that GIBBERELLIN 20 OXIDASE 2, which encodes an enzyme required for biosynthesis of the growth regulator gibberellin (GA), is upregulated in svp mutants. GA is known to promote flowering, and we find that svp mutants contain elevated levels of GA that correlate with GA-related phenotypes such as early flowering and organ elongation. The ga20ox2 mutation suppresses the elevated GA levels and partially suppresses the growth and early flowering phenotypes of svp mutants. In wild-type plants, SVP expression in the shoot apical meristem falls when plants are exposed to photoperiods that induce flowering, and this correlates with increased expression of GA20ox2. Mutations that impair the photoperiodic flowering pathway prevent this downregulation of SVP and the strong increase in expression of GA20ox2. We conclude that SVP delays flowering by repressing GA biosynthesis as well as integrator gene expression and that, in response to inductive photoperiods, repression of SVP contributes to the rise in GA at the shoot apex, promoting rapid induction of flowering.

NO FLOWERING IN SHORT DAY (NFL) is a bHLH transcription factor that promotes flowering specifically under short-day in Arabidopsis

“…Because the GA pathway has strong feedback regulation, as previously shown (Griffiths et al, 2006), these data strongly suggest that nfl is defective in the GA pathway. This behavior is similar to the svp mutant, although svp flowers late under both LD and SD conditions (Andres et al, 2014).…”

Seasonal Regulation of Petal Number

“…GA biosynthesis is known to be regulated by the photoperiod pathway. In long days, SVP expression falls and contributes to increasing the levels of GA, which accelerates flowering by promoting SPL gene transcription (Andrés et al, 2014). Our results indicate that C. hirsuta petal number increases in response to GA application under these long-day conditions.…”

“…The growth hormone GA is another endogenous signal that promotes flowering in Arabidopsis (Eriksson et al, 2006;Andrés et al, 2014). To investigate whether C. hirsuta petal number varies in response to GA levels, we treated C. hirsuta with 0, 0.1, or 10 mM GA 3 .…”

Circadian Clock and Photoperiodic Flowering in Arabidopsis: CONSTANS Is a Hub for Signal Integration

“…Expression of DELLA is controlled by the circadian clock with peak expression in the morning (Arana et al, 2011). In addition to DELLA-CO regulation, expression of the GA biosynthesis genes is negatively regulated by floral repressors, such as SHORT VEGETATIVE PHASE and TEMPRANILLO1 (Osnato et al, 2012;Andrés et al, 2014). It will be of great interest to learn how and when signal integrations of internal or external cues occur to regulate CO function to optimize flowering time to the everchanging environment.…”