Browsing by Author "Rangarajan, Padma"

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    myo-Inositol oxygenase is required for responses to low energy conditions in Arabidopsis thaliana
    Alford, Shannon R.; Rangarajan, Padma; Williams, Phoebe; Gillaspy, Glenda E. (Frontiers, 2012-01-01)
    myo-Inositol is a precursor for cell wall components, is used as a backbone of myo-inositol trisphosphate (Ins(1,4,5)P3) and phosphateidylinositol phosphate signaling molecules, and is debated about whether it is also a precursor in an alternate ascorbic acid synthesis pathway. Plants control inositol homeostasis by regulation of key enzymes involved in myo-inositol synthesis and catabolism. Recent transcriptional profiling data indicate up-regulation of the myo-inositol oxygenase (MIOX) genes under conditions in which energy or nutrients are limited. To test whether the MIOX genes are required for responses to low energy, we first examined MIOX2 and MIOX4 gene expression regulation by energy/nutrient conditions. We found that both MIOX2 and MIOX4 expression are suppressed by exogenous glucose addition in the shoot, but not in the root. Both genes were abundantly expressed during low energy/nutrient conditions. Loss-of-function mutants in MIOX genes contain alterations in myo-inositol levels and growth changes in the root. Miox2 mutants can be complemented with a MIOX2:green fluorescent protein fusion. Further we show here that MIOX2 is a cytoplasmic protein, while MIOX4 is present mostly in the cytoplasm, but also occasionally in the nucleus. Together, these data suggest that MIOX catabolism in the shoot may influence root growth responses during low energy/nutrient conditions.
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    Regulation of Sucrose non-Fermenting Related Kinase 1 genes in Arabidopsis thaliana
    Williams, Sarah P.; Rangarajan, Padma; Donahue, Janet L.; Hess, Jenna S.; Gillaspy, Glenda E. (2014-07-10)
    The Sucrose non-Fermenting Related Kinase 1( SnRK1) proteins have been linked to regulation of energy and stress signaling in eukaryotes. In plants, there is a small SnRK1 gene family. While the SnRK1.1 gene has been well studied, the role other SnRK1 isoforms play in energy or stress signaling is less well understood. We used promoter:GUS analysis and found SnRK1.1is broadly expressed, while SnRK1.2 is spatially restricted. SnRK1.2 is expressed most abundantly in hydathodes, at the base of leaf primordia, and in vascular tissues within both shoots and roots. We examined the impact that sugars have on SnRK1 gene expression and found that trehalose induces SnRK1.2 expression. Given that the SnRK1.1 and SnRK1.2 proteins are very similar at the amino acid level, we sought to address whether SnRK1.2 is capable of re-programming growth and development as has been seen previously with SnRK1.1 over expression. While gain-of-function transgenic plants over expressing two different isoforms of SnRK1.1 flower late as seen previously in other SnRK1.1 over expressors, SnRK1.2 over expressors flower early. In addition, SnRK1.2 over expressors have increased leaf size and rosette diameter during. Early development, which is the opposite of SnRK1.1 over expressors. We also investigated whether SnRK1.2 was localized to similar subcellular compartments as SnRK1.1, and found that both accumulate in the nucleus and cytoplasm in transient expression assays. In addition, we found SnRK1.1 accumulates in small puncta that appear after a mechanical wounding stress. Together, these data suggest key differences in regulation of the SnRK1.1 and SnRK1.2 genes in plants, and highlights differences over expression of each gene has on the development of Arabidopsis.
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    The Role of Arabidopsis thaliana P80 in Inositol Signaling
    Rangarajan, Padma (Virginia Tech, 2013-06-14)
    The myo-inositol signaling pathway in plants allows them to sense external environmental stimuli and respond to them. This signaling pathway depends on the dynamic levels of the second messenger, inositol(1,4,5)trisphosphate, which in turn is regulated by inositol polyphosphate 5-phosphatases (5PTases). Previous studies have shown that 5PTase 13 binds an important energy sensor, Sucrose non-fermenting (Snf) 1-related kinase (SnRK1.1) and also a novel protein P80. Studies from the lab have also shown that P80 is a part of a deubiquitinating enzyme complex along with WDR20 and Ubiquitin-specific protease called UBP3. Our p80 mutants have a root deficient phenotype under low energy conditions which is normalized by addition of sucrose. p80 mutants show reduced growth and early senescence under specific environmental conditions. This is opposite in nature to SnRK1.1 overexpressors. In this study, I have examined the possible interaction of P80 with SnRK1. I have studied the effects of expression of the exogenous SnRK1.1:GFP transgene under the control of the 35S CaMV promoter in the p80 mutant. This will facilitate the delineation of mechanisms that plants use for the control of energy sensing. I also examined the effects of the overexpression of SnRK1.2:GFP in the p80 mutant. Further, I have explored the presence of a new class of molecules, inositol phosphate molecules (InsPs) containing pyrophosphate bonds (PPx) in p80 mutants. Recent evidence has shown that this class of molecules has roles in sensing and signaling. I have demonstrated that InsP7 is present in developing seeds and vegetative tissue of higher plants. I have also demonstrated that p80 mutants have an alteration in the levels of PPx-InsPs. In addition, I have established spatial expression patterns of two enzymes involved in the synthesis of PPx-InsPx, known as VIP kinases. These studies will help resolve how PPx-InsPs are regulated in plants and thus help in their functional characterization.