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Background <p>Cyclin-dependent kinases (CDKs) critically regulate plant cell cycle transitions, including mitosis-to-endoreduplication switches essential for growth and adaptation. In <i>Medicago truncatula</i>, nodules form through symbiotic nitrogen fixation with rhizobia. The terminal differentiation of bacteroids within nodule cells is critical for efficient nitrogen fixation. To maintain and optimize the functionality of these differentiated symbiosomes, host nodule cells undergo repeated rounds of endoreduplication. However, which <i>CDKs</i> are involved in regulating endoreduplication in nodule cells to support effective symbiotic nitrogen fixation remains largely unknown.</p> Results <p>We identified and characterized 29 <i>CDK</i> genes (15 <i>CDKs</i> and 14 <i>CDKLs</i>) classified into eight conserved subgroups. These genes displayed diverse exon/intron structures and protein motifs, with <i>CDKA</i>, <i>CDKB</i>, and <i>CDKL</i> subfamilies showing strong conservation with <i>Arabidopsis thaliana</i>. Expression analysis revealed specific downregulation of <i>CDKB1;1</i>, <i>CDKB2;2</i>, and <i>CDKL13</i> in nodule infection to fixation zones. Protein–protein interaction (PPI) network and Gene ontology (GO) analyses demonstrated <i>CDKB1;1</i> and <i>CDKB2;2</i> involvement in cell cycle regulation. Overexpression of <i>CDKB1;1</i> or <i>CDKB2;2</i> disrupted endoreduplication and nitrogen fixation, with <i>CDKB1;1</i> having the most pronounced effect, while <i>CDKL13</i> appeared dispensable for symbiosis.</p> Conclusion <p>Our study presents the comprehensive genome-wide analysis of the <i>CDK</i> gene family in <i>M. truncatula</i>, demonstrating that the essential role of <i>CDKB1;1</i> and <i>CDKB2;2</i> downregulation in symbiotic nitrogen fixation and endoreduplication offers new insights into cell cycle regulation in nodules. It also identifies potential targets for improving nitrogen fixation efficiency in legumes.</p>

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Identification and functional evaluation of cyclin-dependent kinase genes reveals that CDKB1;1 and CDKB2;2 contribute to the balance of mitosis and endoreduplication in Medicago truncatula nodule

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  • 发表日期：

    2025年11月21日

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  • Rong Wang,
  • Huairong Pan

摘要

Background

Cyclin-dependent kinases (CDKs) critically regulate plant cell cycle transitions, including mitosis-to-endoreduplication switches essential for growth and adaptation. In Medicago truncatula, nodules form through symbiotic nitrogen fixation with rhizobia. The terminal differentiation of bacteroids within nodule cells is critical for efficient nitrogen fixation. To maintain and optimize the functionality of these differentiated symbiosomes, host nodule cells undergo repeated rounds of endoreduplication. However, which CDKs are involved in regulating endoreduplication in nodule cells to support effective symbiotic nitrogen fixation remains largely unknown.

Results

We identified and characterized 29 CDK genes (15 CDKs and 14 CDKLs) classified into eight conserved subgroups. These genes displayed diverse exon/intron structures and protein motifs, with CDKA, CDKB, and CDKL subfamilies showing strong conservation with Arabidopsis thaliana. Expression analysis revealed specific downregulation of CDKB1;1, CDKB2;2, and CDKL13 in nodule infection to fixation zones. Protein–protein interaction (PPI) network and Gene ontology (GO) analyses demonstrated CDKB1;1 and CDKB2;2 involvement in cell cycle regulation. Overexpression of CDKB1;1 or CDKB2;2 disrupted endoreduplication and nitrogen fixation, with CDKB1;1 having the most pronounced effect, while CDKL13 appeared dispensable for symbiosis.

Conclusion

Our study presents the comprehensive genome-wide analysis of the CDK gene family in M. truncatula, demonstrating that the essential role of CDKB1;1 and CDKB2;2 downregulation in symbiotic nitrogen fixation and endoreduplication offers new insights into cell cycle regulation in nodules. It also identifies potential targets for improving nitrogen fixation efficiency in legumes.