Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering
Thursday, 2016/07/07 | 08:07:31
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Shu Yuan, Zhong-Wei Zhang, Chong Zheng, Zhong-Yi Zhao, Yu Wang, Ling-Yang Feng, Guoqi Niu, Chang-Quan Wang, Jian-Hui Wang, Hong Feng, Fei Xu, Fang Bao, Yong Hu, Ying Cao, Ligeng Ma, Haiyang Wang, Dong-Dong Kong, Wei Xiao, Hong-Hui Lin, and Yikun He SignificanceOverapplication of nitrogen (N) fertilizer causes delayed flowering and negatively impacts the function and composition of natural ecosystems and climate. In this study, we demonstrate that flowering time variations regulated by altered nitrogen levels are mediated by two key factors: ferredoxin-NADP+-oxidoreductase (FNR1) and the blue-light receptor cryptochrome 1 (CRY1). Nitrogen regulates FNR1 expression, thereby contributing to changes in NADPH/NADP+ and ATP/AMP ratios, which in turn activates adenosine monophosphate-activated protein kinase to modulate nuclear CRY1 abundance, which further acts in the N signal input pathway to affect central clock function and flowering time. A better understanding of N-regulated floral transition will offer biotechnological solutions to improve sustainable agriculture. AbstractThe 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-of-function 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.
See: http://www.pnas.org/content/113/27/7661.full PNAS July 5 2016; vol.113; no.27: 7661–7666
Fig. 4. N enhances nuclear AMPK activity and phosphorylates and destabilizes nuclear CRY1. (A) Nuclear AMPK activity (N-kinase activity), nuclear AMPK protein level (N-AMPK), and total cellular AMPK protein level (T-AMPK) of WT plants grown under 1/20 LN, NN, or HN conditions over a 24-h period. Autoradiographs are marked with red boxes. (B) Nuclear phosphorylated CRY1 (N-pCRY1), nuclear CRY1 protein level (N-CRY1), and total cellular CRY1 protein level (T-CRY1) of WT plants grown under LN, NN, and HN conditions over a 24-h period. (C) ACTIN1 served as a loading control for total cellular proteins. (D) HISTONE3 served as a loading control for nuclear proteins. |
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