Browsing by Author "Bhardwaj, Akanksha"

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Nodule INception (NIN)-independent epidermal events lead to bacterial entry during nodule development in peanut (Arachis hypogaea)
(John Wiley & Sons, 2022) Bhattacharjee, Oindrila; Raul, Bikash; Ghosh, Amit; Bhardwaj, Akanksha; Bandyopadhyay, Kaustav; Sinharoy, Senjuti
Summary Legumes can host nitrogen-fixing rhizobia inside root nodules. In model legumes, rhizobia enter via infection threads (ITs) and develop nodules where infection-zone contains a mixture of infected and uninfected cells. Peanut (Arachis hypogaea) diversified from model legumes ~50-55 million years ago. Rhizobia enter through ‘cracks’ to form nodules in peanut roots where the cells of infection-zone are uniformly infected. Phylogenomic studies indicated symbiosis as a labile trait in peanut. These atypical features prompted us to investigate the molecular mechanism of peanut nodule development. Combining cell biology, genetics, and genomic tools, we visualized the status of hormonal signaling in peanut nodule primordia. Moreover, we dissected the signaling modules of Nodule INception (NIN), a master regulator of both epidermal infection and cortical organogenesis. Cytokinin signaling operates in a broad zone, from the epidermis to the pericycle inside nodule primordia, while auxin signaling is narrower and focused. NIN is involved in the nodule organogenesis, but not in the crack entry. Nodulation Pectate Lyase (NPL), which remodels cell walls during IT-formation, is not required. Whereas Nodule enhanced Glycosyl Hydrolases (AhNGHs) is recruited for cell wall modification during crack entry. While the hormonal regulation is conserved, the function of the NIN signaling modules is diversified in peanut.
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.
RSD-mediated suppression of NIN and NLP2 transcription is crucial for symbiotic nitrogen fixation
(John Wiley & Sons, 2026) Bhardwaj, Akanksha; Gupta, Megha; Bhattacharjee, Oindrila; Raul, Bikash; Ghosh, Asim Kumar; Nagalla, L. V. Sairam; Yadav, Prashant; Bandyopadhyay, Kaustav; Ranjan, Aashish; Sinharoy, Senjuti
Indeterminate nodules establish a developmental gradient along their longitudinal axis, separating cell differentiation from symbiotic nitrogen fixation (SNF). The apex contains differentiating cells, while the differentiated leghemoglobin-rich cells of the nitrogen-fixation zone shield the rhizobial nitrogenase complex from oxygen to facilitate SNF. By combining biochemical, genetic, and genomic approaches, we demonstrate the pivotal role of the Regulator of Symbiosome Differentiation (RSD), a transcriptional repressor, in the transition from symbiosome development to SNF. Interacting Protein of DMI3 (IPD3) activates RSD expression in the invasion zone (ZII) and interzone (IZ). RSD interacts with Nodule Inception (NIN), and NIN-like protein 2 (NLP2) through a novel protein-protein interaction domain. RSD determines cell fate in ZII and the IZ by suppressing several targets of NIN and NLP2, including Leghemoglobins, Nodule-specific Cysteine-Rich genes, and Symbiotic Cysteine-rich Receptor-like Kinase. Our findings underscore the critical role of RSD-mediated suppression of transcription in facilitating the transition from bacteroid differentiation to SNF.