Browsing by Author "Udvardi, Michael K"

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    The nodule-specific PLAT-domain protein NPD1 is required for nitrogen-fixing symbiosis
    (American Society of Plant Biologists, 2019) Pislariu, Catalina I.; Sinharoy, Senjuti; Torres-Jerez, Ivone; Nakashima, Jin; Blancaflor, Elison B.; Udvardi, Michael K
    Symbiotic nitrogen fixation by rhizobia in legume root nodules is a key source of nitrogen for sustainable agriculture. Genetic approaches have revealed important roles for only a few of the thousands of plant genes expressed during nodule development and symbiotic nitrogen fixation. Previously, we isolated over one hundred nodulation and nitrogen fixation mutants from a population of Tnt1-insertion mutants of Medigaco truncatula (Pislariu et al., 2011). Using Tnt1 as a tag to identify genetic lesions in these mutants, we discovered that insertions in a nodule-specific PLAT (Polycystin-1, Lipoxygenase, Alpha-Toxin) domain-encoding gene, MtNPD1, resulted in development of ineffective nodules. Early stages of nodule development and colonization by the nitrogen fixing bacterium Sinorhizobium meliloti appeared to be normal in the npd1 mutant. However, npd1 nodules ceased to grow after a few days, resulting in abnormally small, ineffective nodules. Rhizobia that colonized developing npd1 nodules did not differentiate completely into nitrogen-fixing bacteroids and quickly degraded. MtNPD1 expression was low in roots but increased significantly in developing nodules four days post-inoculation (DPI), and expression accompanied invading rhizobia in the nodule infection zone and into the distal nitrogen fixation zone. A functional MtNPD1:GFP fusion protein localized in the space surrounding symbiosomes in infected cells. When ectopically expressed in tobacco (Nicotiana tabacum) leaves, MtNPD1 co-localized with vacuoles and the endoplasmic reticulum. MtNPD1 belongs to a cluster of 5 nodule-specific single PLAT domain-encoding genes, with apparent non-redundant functions.
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    Organized peripheral vascular strand development in nodules is controlled by a bHLH/HLH heterodimer
    (John Wiley & Sons, 2026) Srivastava, Deevita; Bhadu, Vikash; Sahoo, Rudra Narayan; Ghosh, Asim Kumar; Upadhyay, Priya; Bhardwaj, Akanksha; Udvardi, Michael K; Ranjan, Aashish; Sinharoy, Senjuti
    The Leguminosae family can develop root nodules with symmetrical peripheral vascular-strands (PVSs). Medicago truncatula forms indeterminate nodules with PVSs. The PVSs elongate directly from the root toward the nodule apex, maintaining a symmetrical organization and facilitating the formation of the cylindrical nodule structure. By combining genetic, biochemical, and genomic tools, we have shown that two basic Helix-Loop-Helix groups of transcription factors, MtbHLH1 (renamed Nodule Vascular bundle Development 1 (NVD1)) and NVD2, control the development of symmetrical PVSs in M. truncatula. In nvd1 nodules, PVSs drift toward the infection zone, generating aberrantly shaped nodules. NVD1 activates its expression along with NVD2, a transcriptional regulator. NVD1 functions downstream of auxin signaling. Transcriptome sequencing of nvd1 and nvd2 nodules, combined with visualization of auxin and cytokinin (CK) signal outputs, revealed disrupted auxin and CK signaling in nvd nodules. Furthermore, ectopic expression of the auxin biosynthetic enzyme (MtYUCCA8) under pMtNVD1 and pMtNVD2 resulted in defective PVSs. Mutant nvd2 nodules display asymmetric PVSs. NVD2 regulates the transcriptional activity of NVD1 by forming heterodimers with it. The formation of symmetrical PVSs depends on the balanced presence of NVD1 and NVD2. Our findings highlight the pivotal role of the NVD1-NVD2 interaction in shaping the development of symmetrical PVSs.