J Integr Plant Biol.

• Research Articles •    

Circadian rhythms driving a fast-paced root clock implicate species-specific regulation in Medicago truncatula

Liping Wang1,2 , Anqi Zhou1,2, Jing Li1,2, Mingkang Yang1,2, Fan Bu1,2, Liangfa Ge3,4,5, Liang Chen1,2* and Wei Huang1,2,6*   

  1. 1 State Key Laboratory for Conservation and Utilization of Subtropical Agro‐Bioresources, South China Agricultural University, Guangzhou 510642, China
    2 College of Life Sciences, South China Agricultural University, Guangzhou 510642, China
    3 Department of Grassland Science, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou 510642, China
    4 Guangdong Engineering Research Center for Grassland Science, Guangzhou 510642, China
    5 Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, South China Agricultural University, Guangzhou 510642, China
    6 Guangdong Provincial Key Laboratory of Protein Function and Regulation in Agricultural Organisms, College of Life Sciences, South China Agricultural University, Guangzhou 510642, China

    *Correspondences: Liang Chen (chenliang@scau.edu.cn); Wei Huang (weihuang@scau.edu.cn, Dr. Huang is fully responsible for the distribution of the materials associated with this article)
  • Received:2021-01-18 Accepted:2021-05-13 Online:2021-05-19

Abstract: Plants have a hierarchical circadian structure comprising multiple tissue-specific oscillators that operate at different speeds and regulate the expression of distinct sets of genes in different organs. However, the identity of the genes differentially regulated by the circadian clock in different organs, such as roots, and how their oscillations create functional specialization remain unclear. Here, we profiled the diurnal and circadian landscapes of the shoots and roots of Medicago truncatula and identified the conserved regulatory sequences contributing to transcriptome oscillations in each organ. We found that the light-dark cycles strongly affect the global transcriptome oscillation in roots, and many clock genes oscillate only in shoots. Moreover, many key genes involved in nitrogen fixation are regulated by circadian rhythms. Surprisingly, the root clock runs faster than the shoot clock, which is contrary to the hierarchical circadian structure showing a slow-paced root clock in both detached and intact Arabidopsis thaliana (L.) Heynh. roots. Our result provides important clues about the species-specific circadian regulatory mechanism, which is often overlooked, and possibly coordinates the timing between shoots and roots independent of the current prevailing model.

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