Professor Indian Institute of Technology Kharagpur, Kharagpur-721302, India Kharagpur, West Bengal, India
Body of Abstract: Transcription factors in coordination with phytohormones form an intricate network to modulate differential gene expression essential for cellular mechanisms in plants. Root system is of great significance as it helps the sessile plant to anchor to the substrate (soil), and is responsible for nutrient and water uptake, first level of protection against biotic and abiotic stresses, and hence the vitality of the plant. In this study, we have functionally characterized the transcription factor OsNAC121 by developing gene silencing as well as overexpressing transgenic rice plants, followed by detailed analyses of the root architecture and root-associated stress adaptation against salt and drought. OsNAC121 gene is highly induced by phytohormones- cytokinin, auxin and abscisic acid. qRT-PCR results clearly showed differential expression of cytokinin biosynthesis- and degradation-associated genes in the root tissues, indicating altered cytokinin levels. In silico studies revealed that OsNAC121 interacts with universal co-repressor (TOPLESS) proteins and forms a part of the inhibitor complex. This repressor complex is an essential core component of auxin signalling pathway. Transgenic lines exhibited remodelling in crown root development and lateral root structure and density, underpinning the auxin:cytokinin imbalanced ratio due to the perturbed auxin transportation. Impaired auxin transport also crippled gravitropic response in the transgenic lines. Since OsNAC121 has crucial role in root architecture and drought and salinity stresses are perceived by roots; we were intrigued to know if OsNAC121 has any role in stress tolerance. Transgenic lines exposed to drought (water deprivation) and salinity (100 mM NaCl) stresses were much healthier compared to untransformed rice plants, implying the role of OsNAC121 in osmotic stress tolerance. Altogether, our findings demonstrate that OsNAC121 regulates the root architecture in rice plant via modulating auxin and cytokinin homeostasis and is involved in osmotic stress-responsive mechanisms.