Nodule-specific cysteine-rich peptide 343 is required for symbiotic nitrogen fixation in Medicago truncatula

Zhang, Rui and Shen, Yitong and He, Juanxia and Zhang, Chenyan and Ma, Yelin and Sun, Chenghui and Song, Xiaopan and Li, Li and Zhang, Sisi and Biró, János Barnabás and Saifi, Farheen and Kaló, Péter and Chen, Rujin (2023) Nodule-specific cysteine-rich peptide 343 is required for symbiotic nitrogen fixation in Medicago truncatula. PLANT PHYSIOLOGY. ISSN 0032-0889 (In Press)

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Abstract

Symbiotic interactions between legumes and rhizobia lead to the development of root nodules and nitrogen fixation by differentiated bacteroids within nodules. Differentiation of the endosymbionts is reversible or terminal, determined by plant effectors. In inverted repeat lacking clade legumes, nodule-specific cysteine-rich (NCR) peptides control the terminal differentiation of bacteroids. Medicago truncatula contains ∼700 NCR-coding genes. However, the role of few NCR peptides has been demonstrated. Here, we report characterization of fast neutron 2106 (FN2106), a symbiotic nitrogen fixation defective (fix−) mutant of M. truncatula. Using a transcript-based approach, together with linkage and complementation tests, we showed that loss-of-function of NCR343 results in impaired bacteroid differentiation and/or maintenance and premature nodule senescence of the FN2106 mutant. NCR343 was specifically expressed in nodules. Subcellular localization studies showed that the functional NCR343-YFP fusion protein colocalizes with bacteroids in symbiosomes in infected nodule cells. Transcriptomic analyses identified senescence-, but not defense-related genes, as being significantly upregulated in ncr343 (FN2106) nodules. Taken together, results from our phenotypic and transcriptomic analyses of a loss-of-function ncr343 mutant demonstrate an essential role of NCR343 in bacteroid differentiation and/or maintenance required for symbiotic nitrogen fixation.

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