Scientists reveal new fine regulator of plant circadian clock cycle

As the internal timing mechanism of plant cells, the circadian clock enables plants to better adapt to diurnal and seasonal environmental changes caused by the rotation and revolution of the earth by coordinating the rhythm of gene expression and metabolic homeostasis. When the plant’s endogenous circadian clock system is consistent with the external light-dark cycle, the plant will grow optimally. Therefore, maintaining a relatively stable circadian clock cycle is very important for plant growth and development.

Recently, Wang Lei’s team at the Institute of Botany, Chinese Academy of Sciences discovered a class of evolutionarily relatively conserved B-box proteins, of which the fifth subfamily members BBX28 and BBX29 are involved in the fine regulation of the circadian clock cycle. Overexpression of BBX28 or BBX29 and their loss-of-function mutations affect the circadian clock cycle. Through protein interaction screening, the team found that BBX28 and BBX29 can directly interact with PRR9, PRR7 and PRR5 proteins, the core components of the central oscillator of the biological clock, in the nucleus, and can enhance the transcriptional repression activity of PRRs proteins on target genes. Transcriptome analysis found that BBX28 and BBX29 mainly inhibited the gene expression of the morning transcription peak, and the two had functional redundancy in the regulation of gene expression, of which BBX28 played a major role. The joint analysis of RNA-Seq and ChIP-seq data found that BBX28/BBX29 and PRRs are in the same pathway in the regulation of circadian clock genes, and coordinately regulate the circadian clock genes expressed in the morning. In addition, the study found that the transcription levels of BBX28 and BBX29 are also feedback-regulated by PRRs proteins, which further enhances the stability of the circadian clock.

This study discovered new circadian clock regulators BBX28 and BBX29, and revealed the mechanism by which these regulators finely regulate the circadian clock cycle by interacting with the core components of the circadian clock, PRRs. BBX28 and BBX29 are evolutionarily conserved BBXs proteins. This study may provide reference for the regulation mechanism of circadian clock in other crops such as rice and soybean.

Recently, relevant research results were published online in “Plants, Cells and Environment” (Plant, Cell & Environment)superior. The research work is supported by the Chinese Academy of Sciences Strategic Leading Science and Technology Project (Type B) and the National Natural Science Foundation of China.

A working model for the fine regulation of circadian clock cycles by BBX28/BBX29. BBX28 and BBX29, members of the fifth subfamily of B-Box, can interact with the core components of the circadian clock, PRR9, PRR7, and PRR5 in the nucleus, and enhance the gene transcriptional repression activity of PRR9, PRR7, and PRR5 during the morning expression phase. At the same time, the expression of BBX28 and BBX29 is repressed by the transcription of PRR9, PRR7 and PRR5 proteins, thereby enhancing the stability of the circadian clock system.

Institute of Botany

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