https://doi.org/10.1073/pnas.1916434117 Significance: The MEP pathway is an essential and evolutionarily conserved metabolic route present in most pathogenic bacteria, plants, and malaria; and hence a target for discovery of agricultural and medical applications, and an engineering template for production of isoprenoids. The essential nature of this pathway and inherent intricacies associated with enzyme activity assays have hampered in vivo structure and functional analyses. Here, we report the suppressor screen leading to identification of 3 functionally conserved amino-acid residues positioned at the active site cavity and cofactor binding domain of the key MEP-pathway enzyme, HDS. The proposed roles of these residues in determining HDS enzyme activity and the MEP-pathway flux offer a platform for rational design of antiinfective drugs and synthetic engineering of isoprenoids. Abstract: The methylerythritol phosphate (MEP) pathway is responsible for producing isoprenoids, metabolites with essential functions in the bacterial kingdom and plastid-bearing organisms including plants and Apicomplexa. Additionally, the MEP-pathway intermediate methylerythritol cyclodiphosphate (MEcPP) serves as a plastid-to-nucleus retrograde signal. A suppressor screen of the high MEcPP accumulating mutant plant ceh1 Rceh1 3 ( ) led to the isolation of 3 revertants (designated - ) resulting from independent intragenic substitutions of conserved amino acids in the penultimate MEP-pathway enzyme, hydroxymethylbutenyl ceh1 diphosphate synthase (HDS). The revertants accumulate varying MEcPP levels, lower than that of , and exhibit partial or full recovery of MEcPP-mediated phenotypes, including stunted growth and induced expression of stress response genes and the corresponding metabolites. Structural modeling of HDS and ligand docking spatially position the substituted residues at the MEcPP binding pocket and cofactor binding domain of ceh1 the enzyme. Complementation assays confirm the role of these residues in suppressing the mutant phenotypes, albeit to different degrees. In vitro enzyme assays of wild type and HDS variants exhibit differential activities and reveal an unanticipated mismatch between enzyme kinetics and the in vivo MEcPP Rceh levels in the corresponding lines. Additional analyses attribute the mismatch, in part, to the abundance of the first and rate-limiting MEP-pathway enzyme, DXS, and further suggest MEcPP as a rheostat for abundance of the upstream enzyme instrumental in fine-tuning of the pathway flux. Collectively, this study identifies critical residues of a key MEP-pathway enzyme, HDS, valuable for synthetic engineering of isoprenoids, and as potential targets for rational design of antiinfective drugs.

Wang, J., Song, H., Wang, Y., 2020. Investigation on the micro-flow mechanism of enhanced oil recovery by low- salinity water flooding in carbonate reservoir. Fuel 266, 117156.

http://www.sciencedirect.com/science/article/pii/S0016236120301514 Low-salinity water flooding has become a significant way to develop carbonate reservoirs in recent years. Clarifying the micro-flow mechanism of low-salinity water flooding (LSWF) on enhanced oil recovery (EOR) becomes the focus of this issue. In this paper, firstly, we conducted a series of experiments to prove that LSWF can improve the recovery of carbonate reservoirs. And then, a new relative permeability model and water content calculation model are established considering interface micro-forces and capillary pressure. The result shows that the present model has good agreement with the experimental results, which can characterize the micro-displacement mechanism of LSWF. The recovery rate can be increased by 9% compared with the formation water flooding (FWF). Under low-salinity conditions, the wettability of rock surface is changed by 2+ 2+ 2- the chemical reaction of divalent ions (Ca , Mg , SO ), which shows more hydrophilic. And the optimal 4 salinity of the brine range from 1400 mg/L to 3200 mg/L. Besides, LSWF can reduce the residual oil saturation, which is the macro cause for EOR. This study has provided a quick and reasonable guide to know the micro- flow mechanism of LSWF and theoretical basis for development of carbonate reservoirs by LSWF.

Wang, P., Du, Y., Yu, W., Algeo, T.J., Zhou, Q., Xu, Y., Qi, L., Yuan, L., Pan, W., 2020. The chemical index of alteration (CIA) as a proxy for climate change during glacial-interglacial transitions in Earth history. Earth- Science Reviews 201, 103032.

http://www.sciencedirect.com/science/article/pii/S0012825219305550