Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering

Abstract

The phenomenon of delayed flowering after the application of nitrogen (N) fertilizer has long been known in agriculture, but the detailed molecular basis for this phenomenon is largely unclear. Here we used a modified method of suppression-subtractive hybridization to identify two key factors involved in N-regulated flowering time control in Arabidopsis thaliana, namely ferredoxin-NADP + -oxidoreductase and the blue-light receptor cryptochrome 1 (CRY1). The expression of both genes is induced by low N levels, and their loss-offunction mutants are insensitive to altered N concentration. Low-N conditions increase both NADPH/NADP + and ATP/AMP ratios, which in turn affect adenosine monophosphate-activated protein kinase (AMPK) activity. Moreover, our results show that the AMPK activity and nuclear localization are rhythmic and inversely correlated with nuclear CRY1 protein abundance. Low-N conditions increase but high-N conditions decrease the expression of several key components of the central oscillator (e.g., CCA1, LHY, and TOC1) and the flowering output genes (e.g., GI and CO). Taken together, our results suggest that N signaling functions as a modulator of nuclear CRY1 protein abundance, as well as the input signal for the central circadian clock to interfere with the normal flowering process. T he transition from vegetative to reproductive development is a central event in the plant life cycle, which is coordinately regulated by various endogenous and external cues. In the model dicotyledonous plant species Arabidopsis thaliana, five distinct genetic pathways regulating flowering time have been established: the vernalization pathway, photoperiod pathway, gibberellin acid (GA) pathway, autonomous pathway, and endogenous (age) pathway (1). These pathways ultimately converge to regulate a set of floral integrator genes, FLOWERING LOCUS T (FT) and SUPPRESSOR OF CONSTANS 1 (SOC1), which in turn activate the expression of floral meristem identity genes to trigger the formation of flowers (2-4).Plants use the circadian clock as the timekeeping mechanism to measure day length and to ensure flowering at the proper season (5, 6). As a facultative long-day (LD) plant, Arabidopsis flowers earlier under LD conditions than under short-day (SD) conditions. Forward genetics in A. thaliana have identified the GI-CO-FT hierarchy as the canonical genetic pathway promoting flowering specifically under LD conditions (5,7,8). In this pathway, GI (GIGANTEA) can be considered the output point of the circadian clock to control flowering by regulating CONSTANS (CO) expression in the right phase, which activates expression of FT and TSF (TWIN SISTER OF FT) in the companion cells of the phloem within the vascular tissue (2, 9). FT and TSF proteins act as the long-sought florigens that move from leaves to the apical meristem to induce genes required for reproductive development (2-4). Both GI and CO are regulated by the circadian clock and by light signaling simultaneously and at both transcriptional and posttranscriptional levels, to en...

Nitrogen regulates CRY1 phosphorylation and circadian clock input pathways

“…Here we find that the high level of AMP under the high N condition activates Arabidopsis AMPKa1. 3 Similar to mammal AMPKs, the AMPKa1 protein in plant cell nuclei also shows a robust rhythm. 3 Furthermore, nuclear activity of AMPKa1 was also higher in the day than at night.…”

“…3 Similar to mammal AMPKs, the AMPKa1 protein in plant cell nuclei also shows a robust rhythm. 3 Furthermore, nuclear activity of AMPKa1 was also higher in the day than at night. In mammal cells, circadian expression of AMPKb2 transcript has been observed.…”

“…[1][2] Here in our study, CRY1 has been identified as the pivotal gene in the nitrogen (N)-regulated flowering pathway. 3 N mediates the central oscillator through the CRY1 input pathway. 3 Carbohydrates (C) generate another nutrition signal, which also regulates flowering.…”

“…3 N mediates the central oscillator through the CRY1 input pathway. 3 Carbohydrates (C) generate another nutrition signal, which also regulates flowering. A recent report found that sugars repress the expression of the morning-expressed gene PSEUDORESPONSE REGULATOR 7 (PRR7) and activate the key component the central oscillator CCA1.…”

“…Thus, C and N may regulate flowering through different pathways. Given that nitrogen levels regulate ferredoxin-NADP C -oxidoreductase and ATP synthesis rate (energy metabolism flow), 3,11 nitrogen metabolism and carbon metabolism may be tightly linked with each other. The crosstalk between C metabolite signals and N metabolite signals needs further investigations.…”