Role of Importin-ALPHA in Regulating CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) in Arabidopsis thaliana

Najma, Najma (2025) Role of Importin-ALPHA in Regulating CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) in Arabidopsis thaliana. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Najma (20MS129)) 20MS129_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (16MB)

Abstract

Circadian rhythms in plants synchronize internal physiological and developmental processes with external day-night cycles, optimizing growth, metabolism, and survival in changing environments. Initially, it was presumed that CCA1 used general nuclear import mechanisms without specific importin selectivity. Because CCA1 controls key circadian rhythms, and precise timing and localization of CCA1 activity is critical for regulating gene expression at the correct time of day, general, non-specific nuclear import would be too inefficient. Thus, specific importins might be required to ensure tightly regulated, preferential nuclear import of CCA1 at the right times to maintain accurate circadian rhythms. Therefore, Arabidopsis thaliana T single and double T-DNA mutants of IMPORTIN α1, α2, and α3 were characterized, revealing reduced hypocotyl elongation, enhanced chlorophyll and anthocyanin accumulation, and impaired hormonal responsiveness. Yeast Two-Hybrid assays confirmed a physical interaction between IMPORTIN α1 and CCA1, suggesting a selective nuclear import mechanism. Overexpression of IMPORTIN α1 led to enhanced hypocotyl elongation but reduced pigment levels, supporting its role in growth promotion. Hormonal assays showed that importin mutants retained partial responsiveness to gibberellin, auxin, and brassinosteroids, but responsiveness was markedly impaired in double mutants. These findings propose that IMPORTIN α1 selectively regulates CCA1 nuclear localization, indirectly modulating PIF4 expression and thereby coordinating environmental, hormonal, and circadian signals for plant growth regulation.

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