J Integr Plant Biol. ›› 2023, Vol. 65 ›› Issue (6): 1536-1552.DOI: 10.1111/jipb.13495

• Molecular Physiology • Previous Articles     Next Articles

A high-resolution transcriptomic atlas depicting nitrogen fixation and nodule development in soybean

Baocheng Sun1,2†, Yu Wang1,2†, Qun Yang1†, Han Gao1,2, Haiyu Niu1,2, Yansong Li1,2, Qun Ma1,2, Qing Huan1, Wenfeng Qian1,2* and Bo Ren1,2*   

  1. 1. State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Innovation Academy for Seed Design, Chinese Academy of Sciences, Beijing 100101, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
    These authors contributed equally to this work.
    *Correspondences:Wenfeng Qian(wfqian@genetics.ac.cn);Bo Ren(bren@genetics.ac.cn, Dr. Ren is fully responsible for the distributions of all materials associated with this article)
  • Received:2023-04-14 Accepted:2023-04-17 Online:2023-04-19 Published:2023-06-01

Abstract: Although root nodules are essential for biological nitrogen fixation in legumes, the cell types and molecular regulatory mechanisms contributing to nodule development and nitrogen fixation in determinate nodule legumes, such as soybean (Glycine max), remain incompletely understood. Here, we generated a single-nucleus resolution transcriptomic atlas of soybean roots and nodules at 14 days post inoculation (dpi) and annotated 17 major cell types, including six that are specific to nodules. We identified the specific cell types responsible for each step in the ureides synthesis pathway, which enables spatial compartmentalization of biochemical reactions during soybean nitrogen fixation. By utilizing RNA velocity analysis, we reconstructed the differentiation dynamics of soybean nodules, which differs from those of indeterminate nodules in Medicago truncatula. Moreover, we identified several putative regulators of soybean nodulation and two of these genes, GmbHLH93 and GmSCL1, were as-yet uncharacterized in soybean. Overexpression of each gene in soybean hairy root systems validated their respective roles in nodulation. Notably, enrichment for cytokinin-related genes in soybean nodules led to identification of the cytokinin receptor, GmCRE1, as a prominent component of the nodulation pathway. GmCRE1 knockout in soybean resulted in a striking nodule phenotype with decreased nitrogen fixation zone and depletion of leghemoglobins, accompanied by downregulation of nodule-specific gene expression, as well as almost complete abrogation of biological nitrogen fixation. In summary, this study provides a comprehensive perspective of the cellular landscape during soybean nodulation, shedding light on the underlying metabolic and developmental mechanisms of soybean nodule formation.

Key words: cytokinin, determinate nodule, nitrogen fixation, nodulation, RNA velocity, single nucleus RNA sequencing (snRNA-seq), soybean, ureide

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