HUA ENHANCER1 Is Involved in Posttranscriptional Regulation of Positive and Negative Regulators in <i>Arabidopsis</i> Photomorphogenesis

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...

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“…S3), in disagreement with previous reports (17,19) but consistent with reported transcriptome analyses (20,21).…”

Section: Resultscontrasting

confidence: 57%

Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering

Yuan

Zhang

Zheng

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

113

103

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“…In cases in which HEN1 is upregulated (for example, by light), a concomitant increase in the HEN1 protein level was observed, resulting in increased levels of miRNAs (Tsai et al 2014). The expression of HEN1 was upregulated in rolB-transformed cells (Fig.…”

Section: Resultsmentioning

confidence: 93%

The rolB gene activates the expression of genes encoding microRNA processing machinery

2014

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The rolB gene of Agrobacterium rhizogenes renders cells more tolerant of environmental stresses and increases their defense potential. However, these effects, coupled with the developmental abnormalities caused by rolB, have not yet been explained. In rolB-transformed Arabidopsis thaliana cells, we detected a 2.2 to 7-fold increase in the expression of genes encoding core and accessory proteins (DCL1, SE, HYL1, AGO1, TGH, DDL, HEN1, AGO4 and RDR2) of the microRNA processing machinery. However, the rolB gene did not affect the expression of DCL2, DCL3 and HST. The diverse and complex effects of rolB on transformed plant cells may be attributable to changes caused by this gene in particular RNA silencing pathways.

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“…This indicates the possible involvement of additional transcriptional regulators of likely minor importance. Next to transcriptional regulation, the expression of HY5 was recently shown to involve light-regulated posttranscriptional regulation by the small regulatory microRNA miR157d (Tsai et al, 2014); however, whether UV-B affects miR157d expression remains unknown. This notwithstanding, HY5 and HYH both associate with the HY5 promoter and are required in vivo for mediation of the early event of HY5 gene induction, which strengthens the concept of their central regulatory role in rapid UV-B responses downstream of UVR8.…”

Section: Regulation Of the Hy5 Promotermentioning

confidence: 99%

UV-B-Responsive Association of the Arabidopsis bZIP Transcription Factor ELONGATED HYPOCOTYL5 with Target Genes, Including Its Own Promoter

et al. 2014

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In plants subjected to UV-B radiation, responses are activated that minimize damage caused by UV-B. The bZIP transcription factor ELONGATED HYPOCOTYL5 (HY5) acts downstream of the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8) and promotes UV-B-induced photomorphogenesis and acclimation. Expression of HY5 is induced by UV-B; however, the transcription factor(s) that regulate HY5 transcription in response to UV-B and the impact of UV-B on the association of HY5 with its target promoters are currently unclear. Here, we show that HY5 binding to the promoters of UV-B-responsive genes is enhanced by UV-B in a UVR8-dependent manner in Arabidopsis thaliana. In agreement, overexpression of REPRESSOR OF UV-B PHOTOMORPHOGENESIS2, a negative regulator of UVR8 function, blocks UV-B-responsive HY5 enrichment at target promoters. Moreover, we have identified a T/G-box in the HY5 promoter that is required for its UV-B responsiveness. We show that HY5 and its homolog HYH bind to the T/G HY5 -box cis-acting element and that they act redundantly in the induction of HY5 expression upon UV-B exposure. Therefore, HY5 is enriched at target promoters in response to UV-B in a UVR8 photoreceptor-dependent manner, and HY5 and HYH interact directly with a T/G-box cis-acting element of the HY5 promoter, mediating the transcriptional activation of HY5 in response to UV-B.

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HUA ENHANCER1 Is Involved in Posttranscriptional Regulation of Positive and Negative Regulators in Arabidopsis Photomorphogenesis

Cited by 49 publications

References 71 publications

Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering

Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering

The rolB gene activates the expression of genes encoding microRNA processing machinery

UV-B-Responsive Association of the Arabidopsis bZIP Transcription Factor ELONGATED HYPOCOTYL5 with Target Genes, Including Its Own Promoter

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