Browsing by Author "Singh, Aparna"

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Calmodulin7 plays an important role as transcriptional regulator in Arabidopsis seedling development
(American Society of Plant Biologists, 2008) Kushwaha, Ritu; Singh, Aparna; Chattopadhyay, Sudip
Although calmodulin (CaM) is known to play multiple regulatory roles in eukaryotes, its direct function as transcriptional regulator is unknown. Furthermore, the physiological functions of CaM are largely unknown in plants. Here, we show that one of the four Arabidopsis thaliana CaM isoforms, CAM7, is a transcriptional regulator that directly interacts with the promoters of light-inducible genes and promotes photomorphogenesis. CAM7 overexpression causes hyperphotomorphogenic growth and an increase in the expression of light-inducible genes. Mutations in CAM7 produce no visible effects on photomorphogenic growth, indicating likely redundant gene functions. However, cam7 mutants display reduced expression of light-inducible genes, and cam7 hy5 double mutants show an enhancement of the hy5 phenotype. Moreover, over- expression of CAM7 can partly suppress the hy5 phenotype, indicating that the two factors work together to control light- induced seedling development. The mutational and transgenic studies, together with physiological analyses, illustrate the concerted function of CAM7 and HY5 basic leucine zipper transcription factor in Arabidopsis seedling development.
Functional relationship of GBF1 with HY5 and HYH in genome-wide gene expression in Arabidopsis
(Springer, 2016) Ram, Hathi; Jain, Mukesh; Singh, Aparna; Chattopadhyay, Sudip
Transcriptional networks play important roles in the regulation of biological processes through coordinated activation or repression of downstream target genes. Arabidopsis bZIP transcription factors, GBF1, HY5, and HYH, interact and heterodimerize with each other to form the regulatory network in photomorphogenesis. The genome-wide direct target genes of GBF1 and the roles of HY5 and HYH in controlling GBF1’s genome-wide DNA binding ability have been shown earlier. However, the GBF1 regulated genes at global scale, and how HY5 and HYH modulate GBF1-mediated genome-wide gene expression remain unknown. Here, we report the genome-wide gene expression profile in gbf1, gbf1 hy5, and gbf1 hyh mutants. Our results suggest that HY5 and HYH antagonistically regulate GBF1-mediated global gene expression. We validated the microarray analysis with independent qPCR analyses. Functional analysis of GBF1-regulated genes validates previously known roles of GBF1 in important biological processes. Furthermore, the data also highlight possible novel role of GBF1 in several other biological processes. The previous ChIP-chip results and this transcriptome data together demonstrate the complex transcriptional regulatory mechanism of these transcription factors, GBF1, HY5, and HYH, in photomorphogenesis.
GBF 1, a transcription factor of blue light signaling in Arabidopsis, is degraded in the dark by a proteasome-mediated pathway independent of COP 1 and SPA 1
(The American Society for Biochemistry and Molecular Biology, Inc., 2008) Mallappa, Chandrashekara; Singh, Aparna; Ram, Hathi; Chattopadhyay, Sudip
Arabidopsis GBF1/ZBF2 is a bZIP transcription factor that plays dual but opposite regulatory roles in cryptochrome-mediated blue light signaling. Here, we show the genetic and molecular interrelation of GBF1 with two well characterized negative regulators of light signaling, COP1 and SPA1, in photomorphogenic growth and light-regulated gene expression. Our results further reveal that GBF1 protein is less abundant in the dark- grown seedlings and is degraded by a proteasome-mediated pathway independent of COP1 and SPA1. Furthermore, COP1 physically interacts with GBF1 and is required for the optimum accumulation of GBF1 protein in light-grown seedlings. Taken together, this study provides a mechanistic view of concerted function of three important regulators in Arabidopsis seedling development.
Molecular interactions of GBF1 with HY5 and HYH during light-mediated seedling development in Arabidopsis thaliana
(American Society for Biochemistry and Molecular Biology, 2012) Singh, Aparna; Ram, Hathi; Abbas, Nazia; Chattopadhyay, Sudip
Arabidopsis bZIP transcription factor, GBF1, acts as a differential regulator of cryptochrome-mediated blue light signaling. Whereas the bZIP proteins, HY5 (elongated hypocotyl 5) and HYH (HY5 homologue), are degraded by COP1-mediated proteasomal pathways, GBF1 is degraded by a proteasomal pathway independent of COP1. In this study, we have investigated the functional interrelations of GBF1 with HY5 and HYH in Arabidopsis seedling development. The genetic studies using double and triple mutants reveal that GBF1 largely acts antagonistically with HY5 and HYH in Arabidopsis seedling development. Further, GBF1 and HY5 play more important roles than HYH in blue light-mediated photomorphogenic growth. This study reveals that GBF1 is able to form a G-box-binding heterodimer with HY5 but not with HYH. The in vitro and in vivo studies demonstrate that GBF1 co-localizes with HY5 or HYH in the nucleus and physically interacts with both of the proteins. The protein-protein interaction studies further reveal that the bZIP domain of GBF1 is essential and sufficient for the interaction with HY5 or HYH. Taken together, these data demonstrate the functional interrelations of GBF1 with HY5 and HYH in Arabidopsis seedling development.