On April 16, 2020, Deng Xingwang of Peking University and Xu Dongqing of Nanjing Agricultural University published a research paper on plant communications entitled "a positive feedback loop of bbx11-bbx21-hy5 promoting photogenic development in Arabidopsis", which revealed the new mechanism of plant light signal transduction.
Light is not only a source of energy for photosynthesis, but also an important environmental signal factor for plant growth and development. Photomorphogenesis of plant seedlings is strictly controlled by light signals. The development process is regulated by a molecular network composed of different photoreceptors, E3 ubiquitination ligase complex and transcription factors. In the plant light signal transduction system, members of the BBX (b-box) family play an important role. A number of BBX proteins participate in the cop1-hy5-mediated signal pathway and jointly regulate the plant light morphogenesis (Xu et al., 2016, 2018, Lin et al., 2018; Xu. 2019; Song et al., 2020).
Working model of positive feedback regulation of bbx11-bbx21-hy5 transcription
Light signals initiate nearly one-third of gene expression changes in plants, and ultimately ensure the normal photomorphogenesis of plants to grow into healthy seedlings (MA et al., 2001; Lee et al., 2007). This transcriptional regulation system is controlled by many transcription factors at the molecular level. Three transcription factors BBX11, bbx21 and HY5 are the positive regulators of plant light signal transduction pathway, which coordinate and promote light signal transduction. In the dark, bbx21 and HY5 are degraded by ubiquitination of COP1 – spa E3 ubiquitination ligase complex (Osterlund et al., 2000; Xu et al., 2016), while BBX11 is stabilized by COP1, which may be degraded by an unidentified factor. Therefore, the protein abundances of BBX11, bbx21 and HY5 were very low in the dark, which could not promote the formation of light morphology. Under light, the accumulated bbx21 and HY5 can bind to the promoter region of BBX11 and HY5 respectively and activate their transcription expression; meanwhile, BBX11 can also directly bind to the promoter region of HY5 and positively regulate the expression of HY5 gene. Therefore, these three transcription factors constitute a positive feedback regulation system at the transcription level to participate in the regulation of the expression of more than 3000 genes regulated by light in plants, and promote the formation of plant light morphology in coordination.
Dr. Zhao Xianhai and Dr. Heng Yueqin, senior researcher of Biology Department of South University of science and technology, are the co authors of this paper; Deng Xingwang, academician of Modern Agricultural College of Peking University and Professor Xu Dongqing, Professor of Agricultural College of Nanjing Agricultural University are the co correspondents of this paper; Dr. Wang Xuncheng, postdoctoral of Modern Agricultural College of Peking University, participated in this study. This research was supported by national key research and development program, National Natural Science Foundation, Peking University Tsinghua Life Science Joint Center, South University of science and technology and Nanjing Agricultural University.
reference:
Ma, L., Li, J., Qu, L., Hager, J., Chen, Z., Zhao, H. and Deng, X.W. (2001). Light control of Arabidopsis development entails coordinated regulation of genome expression and cellular pathways. Plant Cell 13:2589 -2607.
Lee, J., He, K., Stolc, V., Lee, H., Figueroa, P., Gao, Y., Tongprasit, W., Zhao, H., Lee, I. and Deng, X.W. (2007). Analysis of transcription factor HY5 genomic binding sites revealed its hierarchical role in light regulation of development. Plant Cell 19:731-749.
Lin, F., Jiang, Y., Li, J., Yan, T., Fan, L., Liang, J., Chen, Z.J., Xu, D. and Deng, X.W. (2018). B-BOX DOMAIN PROTEIN28 negatively regulates photomorphogenesis by repressing the activity of transcription factor HY5 and undergoes COP1-mediated degradation. Plant Cell 30: 2006-2019.
Osterlund, M.T., Hardtke, C.S., Wei, N. and Deng, X.W. (2000). Targeted destabilization of HY5 during light-regulated development of Arabidopsis. Nature 405: 462-466.
Song, Z., Bian, Y., Liu, J., Sun, Y, and Xu, D. (2020). B-box proteins: pivotal players in light-mediated development in plants. J Integr. Plant Biol. doi: 10.1111/jipb.12935.Xu, D. (2019). COP1 and BBXs-HY5-mediated light signal transduction in plants. New Phytol. doi: 10.1111/nph.
Xu, D., Jiang, Y., Li, J., Lin, F., Holm, M., and Deng, X.W. (2018). B-box domain protein BBX21 promotes photomorphogenesis. Plant Physiol. 176: 2365-2375.
Xu, D., Jiang, Y., Li, J., Lin, F., Holm, M. and Deng, X.W. (2016). BBX21, an Arabidopsis B-box protein, directly activates HY5 and is targeted by COP1 for 26S proteasome-mediated degradation. Proc. Natl. Acad. Sci. USA 113: 7655-7660.
Scan and follow us
Micro signal: molblant2019
https://www.cell.com/plant-communications/home