Heat stress commonly leads to inhibition of photosynthesis in higher plants. The transcriptional induction of heat stress-responsive genes represents the first line of inducible defense against imbalances in cellular homeostasis. Although heat stress transcription factor HsfA2 and its downstream target genes are well studied, the regulatory mechanisms by which HsfA2 is activated in response to heat stress remain elusive. Here, we show that chloroplast ribosomal protein S1 (RPS1) is a heat-responsive protein and functions in protein biosynthesis in chloroplast. Knockdown of RPS1 expression in the rps1 mutant nearly eliminates the heat stress-activated expression of HsfA2 and its target genes, leading to a considerable loss of heat tolerance. We further confirm the relationship existed between the downregulation of RPS1 expression and the loss of heat tolerance by generating RNA interference-transgenic lines of RPS1. Consistent with the notion that the inhibited activation of HsfA2 in response to heat stress in the rps1 mutant causes heat-susceptibility, we further demonstrate that overexpression of HsfA2 with a viral promoter leads to constitutive expressions of its target genes in the rps1 mutant, which is sufficient to reestablish lost heat tolerance and recovers heat-susceptible thylakoid stability to wild-type levels. Our findings reveal a heat-responsive retrograde pathway in which chloroplast translation capacity is a critical factor in heat-responsive activation of HsfA2 and its target genes required for cellular homeostasis under heat stress. Thus, RPS1 is an essential yet previously unknown determinant involved in retrograde activation of heat stress responses in higher plants.

Competitive adsorption and diffusion behaviours of CO2/CH4/H2O in brown coal were explored by GCMC and MD simulations.

Understanding the adsorption mechanism of CO2/CH4 in kaolinite clay is essential for the carbon dioxide geological sequestration and enhanced gas recovery in shale reservoirs. In the present work, grand canonical Monte Carlo simulations were employed to investigate the mechanism of competitive adsorption of CO2/CH4 in kaolinite clay. The effects of pore size (1–6 nm), pressure (0.1–30 MPa), temperature (298–378 K), and moisture content (0–0.122 g/cm3) on the adsorption behaviors of pure CH4 and CO2/CH4 mixture were explored in-depth. Specifically, two adsorption layers, i.e., strong and weak adsorption layers, in kaolinite slitlike micropore under high pressure condition have been observed. It was found that pore size and pressure have great effects on the gas adsorption mechanism in kaolinite. The two adsorption mechanisms including monolayer adsorption and micropore filling under high pressure or small pore size conditions were discussed. In addition, simulation results showed that CO2 has much stronger adsorption ability than CH4 in kaolinite. The adsorption capacity of CH4 was significantly suppressed in the presence of CO2, especially in the strong adsorption layer. An adsorption selectivity over 7 has been found in the strong adsorption layer. Temperature and moisture content have great influences on the adsorption capacity and adsorption selectivity. However, the influences have different scales in strong and weak adsorption layers. It is expected the obtained results could provide insights into the adsorption mechanism of CO2/CH4 and offer fundamental data for a CO2 sequestration and enhanced gas recovery (CS-EGR) project in kaolinite clay.

Competitive adsorption behaviour of CO2/CH4 mixture in shale slit nanopores under various geological conditions was explored by molecular simulations.

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The knowledge of adsorption behaviors and mechanism of CO2/CH4 in organic matter is of great importance for CO2 geological sequestration with enhanced gas recovery in shale reservoirs. In this study, the adsorption behaviors and confinement effects of CO2/CH4 in realistic kerogen nanopores have been investigated by using the grand canonical Monte Carlo method. To represent realistic nanopores in the kerogen matrix, the inkbottle-shaped and slit-like nanopores were developed. The effects of temperature, pressure, and pore size on competitive adsorption behaviors and adsorption mechanism of CO2/CH4 were explored. Simulation results indicate that the adsorption capacity of CH4 is lower than that of CO2 in the kerogen matrix with/without kerogen nanopores. A higher pressure and lower temperature are favorable for the adsorption capacities of CO2 and CH4. The gas adsorption capacities have been enhanced in both the inkbottle-shaped and slit-like nanopores. Meanwhile, the existence of inkbottle-shaped micropores is favorable for improving the selectivity of CO2/CH4 in shale organic matter. A higher CO2 injection pressure could improve its adsorption capacity but lower the adsorption selectivity of CO2 over CH4. Furthermore, confinement effects were observed in inkbottle-shaped and slit-like kerogen micropores and small mesopores. Two major factors, including the supercritical state of gas and microscale pores, could enhance the confinement effects. In addition to monolayer adsorption, micropore filling was observed in inkbottle-shaped and slit-like kerogen nanopores because of the confinement effects. It is expected that these results could help in understanding the microscopic adsorption mechanism and provide fundamental information for shale gas exploitation and CO2 sequestration.

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