Biology subjects

Lokdarshi, A.

Publications and source records attributed to Lokdarshi, A..

3 recordsLinked to original sources

bioRxiv2019

Regulator of Gene Silencing-Calmodulin associates with mRNA granules and the autophagy protein ATG8

Abstract Regulator-of-gene-silencing calmodulins (rgsCaM) represent a phylogenetic subfamily of calmodulin-like calcium sensors that are targets of viral induced suppression of posttranscriptional gene silencing by secondary siRNAs. The present work shows that a stress (hypoxia) that induces mRNP granule formation also induces the relocalization of rgsCaM to cytosolic granule-like foci that interact with the surface of stress granule and processing body structures. Co-expression of rgsCaM and its binding protein Suppressor of Gene Silencing 3 causes re-localization and integration of rgsCaM into stress granule structures. RgsCaMs contain a conserved topology that consists for four EF hand like domains (three functional and one divergent) that are separated into two calcium binding lobes with an extended amino terminal region. RgsCaM also contains an "ATG8 family interacting motif" (AIM) within its amino-terminal domain that is characteristic of selective autophagy cargo receptors. Co-localization experiments and ratiometric BiFC analyses in Nicotiana benthamiana support the hypothesis that rgsCaM binds directly to ATG8e through this conserved AIM domain, and the two proteins co-localize with mRNP granule markers. Previous reports show that rgsCaM mediates the suppression of gene silencing, at least in part, via turnover of SGS3 via autophagy. A model is proposed for rgsCaM-like proteins as potential mediators of selective autophagy of RNA granules in response to biotic and abiotic stresses.

plant biology↗

bioRxiv2019

Light dependent activation of the GCN2 kinase under cold and salt stress is mediated by the photosynthetic status of the chloroplast

Regulation of cytosolic mRNA translation is a key node for rapid adaptation to environmental stress conditions. In yeast and animals, phosphorylation of the -subunit of eukaryotic translation initiation factor eIF2 is the most thoroughly characterized event in regulating global translation under stress. In plants, the GCN2 kinase (General Control Non-derepressible-2) is the only known kinase for eIF2. GCN2 is activated under a variety of stresses including reactive oxygen species. Here we provide new evidence that the GCN2 kinase in Arabidopsis is also activated rapidly and in a light dependent manner by cold and salt treatments. These treatments alone did not repress global mRNA ribosome loading in a major way. The activation of GCN2 was attenuated by inhibitors of photosynthesis and antioxidants, suggesting that it is gated by the redox poise or the reactive oxygen status of the chloroplast. In keeping with these results, gcn2 mutant seedlings were more sensitive than wild type to both cold and salt in a root elongation assay. These data suggest that cold and salt stress may both affect the status of the cytosolic translation apparatus via the conserved GCN2-eIF2 module. The potential role of the GCN2 kinase pathway in the global repression of translation under abiotic stress will be discussed.

plant biology↗

bioRxiv2019

Light activates the translational regulatory GCN2 kinase via reactive oxygen species emanating from the chloroplast

Cytosolic mRNA translation is subject to global and mRNA-specific controls. Phosphorylation of translation initiation factor eIF2 anchors a reversible switch that represses translation globally. The stress-responsive GCN2 kinase is the only known kinase for eIF2 in Arabidopsis. Here we show that conditions that generate reactive oxygen species (ROS) in the chloroplast, such as dark-light transitions, high light, and the herbicide methyl viologen all rapidly activated the GCN2 kinase, whereas mitochondrial and ER stress did not. In addition, GCN2 activation was light dependent and mitigated by photosynthesis inhibitors and ROS quenchers. Accordingly, seedling growth of multiple gcn2 mutant alleles was retarded under conditions of excess light, implicating the GCN2-eIF2 pathway in responses to light and associated ROS. Once activated, the GCN2 kinase preferentially suppressed the ribosome loading of mRNAs for functions such as mitochondrial ATP synthesis, the chloroplast thylakoids, vesicle trafficking, and translation. The transcriptome of gcn2 mutants was sensitized to abiotic stress, including oxidative stress, as well as innate immune responses. Accordingly, gcn2 displayed defects in immune priming by the fungal elicitor, chitin. In conclusion, we provide evidence that reactive oxygen species produced by the photosynthetic apparatus help to activate the highly conserved GCN2 kinase, leading to eIF2 phosphorylation and thus affecting the status of the cytosolic protein synthesis apparatus.

plant biology↗