Abstract
Plants exhibit different physiological and molecular responses to adverse changes in their environment. One such molecular response is the sequestration of proteins, RNAs, and metabolites into cytoplasmic bodies called stress granules (cSGs). Here we report that, in addition to cSGs, heat stress also induces the formation of SG-like foci (cGs) in the chloroplasts of the model plant Arabidopsis thaliana. Similarly to the cSGs, (i) cpSG assemble rapidly in response to stress and disappear when the stress ceases, (ii) cpSG formation is inhibited by treatment with a translation inhibitor (lincomycin), and (iii) cpSG are composed of a stable core and a fluid outer shell. A previously published protocol for cSG extraction was successfully adapted to isolate cpSG, followed by protein, metabolite, and RNA analysis. Analogously to the cSGs, cpSG sequester proteins essential for SG formation, dynamics, and function, also including RNA-binding proteins with prion-like domain, ATPases and chaperones, and the amino acids proline and glutamic acid. However, the most intriguing observation relates to the cpSG localization of proteins, such as a complete magnesium chelatase complex, which is involved in photosynthetic acclimation to stress. These data suggest that cpSG have a role in plant stress tolerance.
Highlights
Cell compartmentalization is a way to separate and organize biochemical reactions in order to increase the efficiency of cellular processes
The most important characteristics of Stress granules (SGs) are as follows (Protter and Parker, 2016; Chantarachot and Bailey-Serres, 2018; Youn et al, 2019): (i) SGs form under stress conditions associated with stalled translation, (ii) SGs sequester both proteins and mRNAs, (iii) SGs are characterized by the presence of conserved proteins involved in SG formation and dynamics, such as intrinsically disordered proteins (IDPs), (iv) SGs rapidly assemble under stress conditions and disassemble when the stress ceases, (v) because of their liquid-like properties, SGs can fuse with each other and with other biological condensates such as processing bodies and in the process exchange components (Gutierrez-Beltran et al, 2015), and (vi) SGs are composed of a stable core and more dynamic, fluid shell
To examine the possibility of SGs forming in chloroplasts of higher plants, we expressed one of the 28 plastidial proteins identified in the called stress granules (cSGs), snowy cotyledon 1 (SCO1), as a fusion with green fluorescent protein (GFP) under the control of the constitutive cauliflower mosaic virus (CaMV) 35S promoter
Summary
Cell compartmentalization is a way to separate and organize biochemical reactions in order to increase the efficiency of cellular processes. The most important characteristics of SGs are as follows (Protter and Parker, 2016; Chantarachot and Bailey-Serres, 2018; Youn et al, 2019): (i) SGs form under stress conditions associated with stalled translation, (ii) SGs sequester both proteins and mRNAs, (iii) SGs are characterized by the presence of conserved proteins involved in SG formation and dynamics, such as IDPs, (iv) SGs rapidly assemble under stress conditions and disassemble when the stress ceases, (v) because of their liquid-like properties, SGs can fuse with each other and with other biological condensates such as processing bodies and in the process exchange components (Gutierrez-Beltran et al, 2015), and (vi) SGs are composed of a stable core and more dynamic, fluid shell. Plastidial SGs (cpSG) sequester proteins, mRNAs, and metabolites, including key photosynthetic regulators, indicative of the importance of cpSG for Arabidopsis stress response
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