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End date: 2009Subject: search.filters.subject.Arabidopsis

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    Role of CIPK6 in root growth and auxin transport
    (Landes Bioscience, 2009) Tripathi, Vineeta; Syed, Nazia; Laxmi, Ashverya; Chattopadhyay, Debasis
    In our recent publication,1 we have shown that a T-DNA insertion in Arabidopsis CIPK6 gene encoding a CBL-interacting protein kinase caused reduction in expression of the gene and emergence of lateral roots. The change in phenotype in the mutant line was likely due to reduction in shoot-to-root acro- petal and the root tip basipetal auxin transport. Here we report identification of a homozygous knockout line of AtCIPK6 (atcipk6) with no detectable expression of the gene in normal growth condition. The knockout line exhibited considerable decrease in growth rate of the taproot as well as in emergence of lateral roots. The mutant line also showed reduction in the root tip basipetal and shoot-to-root acropetal auxin transport. Relative rate of auxin transport and the root phenotype of the atcipk6 closely matched with those of pgp4-1, an Arabidopsis line mutated in PGP4. This gene encodes an ABC integral membrane transporter, which functions in polar auxin transport. These observations strengthen our earlier proposal that CIPK6 is probably involved in polar auxin transport and indicate that it may function through the PGP4 auxin transporter.
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    CIPK6, a CBL-interacting protein kinase is required for development and salt tolerance in plant
    (Wiley-Blackwell, 2009) Tripathi, Vineeta; Parasuraman, Boominathan; Laxmi, Ashverya; Chattopadhyay, Debasis
    Calcineurin B-like proteins (CBL) and CBL-interacting protein kinases (CIPK) mediate plant responses to a variety of external stresses. Here we report that Arabidopsis CIPK6 is also required for the growth and development of plants. Phenotype of tobacco plants ectopically expressing a homologous gene (CaCIPK6) from the leguminous plant chickpea (Cicer arietinum) indicated its functional conservation. A lesion in AtCIPK6 significantly reduced shoot-to-root and root basipetal auxin transport, and the plants exhibited developmental defects such as fused cotyledons, swollen hypocotyls and compromised lateral root formation, in conjunction with reduced expression of a number of genes involved in auxin transport and abiotic stress response. The Arabidopsis mutant was more sensitive to salt stress compared to wild-type, while overexpression of a constitutively active mutant of CaCIPK6 promoted salt tolerance in transgenic tobacco. Furthermore, tobacco seedlings expressing the constitutively active mutant of CaCIPK6 showed a developed root system, increased basipetal auxin transport and hypersensitivity to auxin. Our results provide evidence for involvement of a CIPK in auxin transport and consequently in root development, as well as in the salt-stress response, by regulating the expression of genes.
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    Role of glucose in spatial distribution of auxin regulated genes
    (Landes Bioscience, 2009) Gupta, Aditi; Singh, Manjul; Mishra, Bhuwaneshwar S.; Kushwah, Sunita; Laxmi, Ashverya
    Plants have the ability to adjust its physiology and metabolism to the changes of nutrient availability in the environment. Since a number of common responses are regulated by sugar and auxin, the obvious question arises is whether sugar and auxin act interdependently to bring about changes in plant morphology. In the February issue of the PLoS ONE,1 we presented detailed investigation of glucose and auxin signaling interaction in controlling root growth and development in Arabidopsis thaliana seedlings. Further analysis of tissue specific regulation of glucose auxin signaling interaction may provide some insight as to how these two signaling molecules interact to control the morphogenic changes during seedling development.
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    Light-induced phosphorylation and degradation of the negative regulator PIF1 depends upon its direct physical interactions with photoactivated phytochromes
    (American Society of Plant Biologists, 2008) Shen, Hui; Zhu, Ling; Castillon, Alicia; Majee, Manoj; Downie, Bruce; Huq, Enamul
    The phytochrome (phy) family of photoreceptors regulates changes in gene expression in response to red/far-red light signals in part by physically interacting with constitutively nucleus-localized phy-interacting basic helix-loop-helix transcription factors (PIFs). Here, we show that PIF1, the member with the highest affinity for phys, is strongly sensitive to the quality and quantity of light. phyA plays a dominant role in regulating the degradation of PIF1 following initial light exposure, while phyB and phyD and possibly other phys also influence PIF1 degradation after prolonged illumination. PIF1 is rapidly phosphorylated and ubiquitinated under red and far-red light before being degraded with a half-life of ~1 to 2 min under red light. Although PIF1 interacts with phyB through a conserved active phyB binding motif, it interacts with phyA through a novel active phyA binding motif. phy interaction is necessary but not sufficient for the light-induced phosphorylation and degradation of PIF1. Domain-mapping studies reveal that the phy interaction, light-induced degradation, and transcriptional activation domains are located at the N-terminal 150–amino acid region of PIF1. Unlike PIF3, PIF1 does not interact with the two halves of either phyA or phyB separately. Moreover, overexpression of a light-stable truncated form of PIF1 causes constitutively photomorphogenic phenotypes in the dark. Taken together, these data suggest that removal of the negative regulators (e.g., PIFs) by light-induced proteolytic degradation might be sufficient to promote photomorphogenesis.
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    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.
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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.
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    SHORT HYPOCOTYL IN WHITE LIGHT1, a serine-arginine-aspartate rich protein in Arabidopsis, acts as a negative regulator of photomorphogenic growth
    (American Society of Plant Biologists, 2008) Bhatia, Shikha; Gangappa, Sreeramaiah N.; Kuswaha, Ritu; Kundu, Snehangshu; Chattopadhyay, Sudip
    Light is an important factor for plant growth and development. We have identified and functionally characterized a regulatory gene SHORT HYPOCOTYL IN WHITE LIGHT1 (SHW1) involved in Arabidopsis (Arabidopsis thaliana) seedling development. SHW1 encodes a unique serine-arginine-aspartate-rich protein, which is constitutively localized in the nucleus of hypocotyl cells. Transgenic analyses have revealed that the expression of SHW1 is developmentally regulated and is closely associated with the photosynthetically active tissues. Genetic and molecular analyses suggest that SHW1 acts as a negative regulator of light-mediated inhibition of hypocotyl elongation, however, plays a positive regulatory role in light-regulated gene expression. The shw1 mutants also display shorter hypocotyl in dark, and analyses of shw1 cop1 double mutants reveal that SHW1 acts nonredundantly with COP1 to control hypocotyl elongation in the darkness. Taken together, this study provides evidences that SHW1 is a regulatory protein that is functionally interrelated to COP1 and plays dual but opposite regulatory roles in photomorphogenesis.
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    A basic leucine zipper transcription factor, G-box-binding factor 1, regulates blue light-mediated photomorphogenic growth in Arabidopsis
    (The American Society for Biochemistry and Molecular Biology, Inc., 2006) Mallappa, Chandrashekara; Yadav, Vandana; Negi, Prem; Chattopadhyay, Sudip
    Several transcriptional regulators have been identified and demonstrated to play either positive or negative regulatory roles in seedling development. However, the regulatory coordination between hypocotyl elongation and cotyledon expansion during early seedling development in plants remains unknown. We report the identification of a Z-box binding factor (ZBF2) and its functional characterization in cryptochrome-mediated blue light signaling. ZBF2 encodes a G-box binding factor (GBF1), which is a basic leucine zipper transcription factor. Our DNA- protein interaction studies reveal that ZBF2/GBF1 also interacts with the Z-box light-responsive element of light-regulated promoters. Genetic analyses of gbf1 mutants and overexpression studies suggest that GBF1 acts as a repressor of blue light-mediated inhibition in hypocotyl elongation, however, it acts as a positive regulator of cotyledon expansion during photomorphogenic growth. Furthermore, whereas GBF1 acts as a positive regulator of lateral root formation, it differentially regulates the expression of light-inducible genes. Taken together, these results demonstrate that GBF1 is a unique transcriptional regulator of photomorphogenesis in blue light.
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    A basic helix-loop-helix transcription factor in Arabidopsis, MYC2, acts as a repressor of of blue light-mediate photomorphogenic growth
    (American Society of Plant Biologists, 2005) Yadav, Vandana; Mallappa, Chandrashekara; Gangappa, Sreeramaiah N.; Bhatia, Shikha; Chattopadhyay, Sudip
    This work is supported by Department of Biotechnology and Department of Science and Technology grants to S.C. V.Y., C.M., and S.N.G. are recipients of Council of Scientific and Industrial Research fellowships from the government of India.