Biology subjects

Schwartz, A.

Publications and source records attributed to Schwartz, A..

3 recordsLinked to original sources

bioRxiv2018

Expression of a recombinant, 4’-Phosphopantetheinylated, active M. tuberculosis Fatty acid Synthase I in E. coli

Fatty acid synthase 1 (FAS I) from Mycobacterium. tuberculosis (Mtb) is an essential protein and a promising drug target. FAS I is a multi-functional, multi-domain protein that is organized as a large (1.9 MDa) homohexameric complex. Acyl intermediates produced during fatty acid elongation are attached covalently to an acyl carrier protein (ACP) domain. This domain is activated by the transfer of a 4-Phosphopantetheine (4-PP, also termed P-pant) group from CoA to ACP catalyzed by a 4-PP transferase, termed acyl carrier protein synthase (AcpS). In order to obtain an activated FAS I in E. coli, we transformed E. coli with tagged Mtb fas1 and acpS genes encoded by a separate plasmid.\n\nWe induced the expression of Mtb FAS I following induction of AcpS expression. FAS I was purified by Strep-Tactin affinity chromatography. Activation of Mtb FAS I was confirmed by the identification of a bound P-pant group on serine at position 1808 by mass spectrometry. The purified FAS I displayed biochemical activity shown by spectrophotometric analysis of NADPH oxidation and by CoA production, using the Ellman reaction. The purified Mtb FAS I forms a hexameric complex shown by negative staining and cryo-EM. Purified hexameric and active Mtb FAS I is required for binding and drug inhibition studies and for structurefunction analysis of this enzyme. This relatively simple and short procedure for Mtb FAS I production should facilitate studies of this enzyme.

microbiology↗

bioRxiv2018

Long-term acclimation to different stress types: revealing tradeoffs between mesophyll and stomatal conductance

Ziziphus spina-christi, a thermophilic tree, became more abundant in the Mediterranean, presumably due to increased winter temperatures. In order to predict the plant acclimation to future climate changes, we attempted to understand which factors underlie photosynthetic stress acclimation.\n\nStress acclimation to three major long-term abiotic stresses (drought, salinity and temperature) was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. We developed a stress index that allowed to precisely define stress level, enabling a comparison between stress types. For each stress, photosynthesis-limiting factors were compared: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax).\n\nPhotosynthesis under all stresses was limited mostly by gs and gm (80-90%); whereas biochemistry (Vcmax) made a minor contribution (10-20%). The relative contribution of gs and gm on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in gs, while intolerance to low temperatures was driven by decline in gm. Low mesophyll-imposed limitation was the best predictor of abiotic stress tolerance.\n\nThe results demonstrate how warming climate benefits thermophilic species. Moreover, current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change.\n\nHighlightWe have compared the photosynthesis limitation resulting from long-term acclimation to three major a-biotic stresses (drought, salinity and temperature) to understand which limiting-factor are dominant under each type of stress.

plant biology↗

bioRxiv2018

Water availability dynamics have long-term effects on mature stem structure in Vitis vinifera

Vitis vinifera is a climbing vine with wide vessels and high hydraulic conductivity. There is a lack of data on the anatomical structure of the mature vine stem, and most current knowledge is based on first-year shoots. Moreover, the effect of drought stress on anatomical structure has been partly reported in shoots of Vitis vinifera but not in stems.\n\nIn current study two irrigation approaches were applied on Vitis vinifera Merlot vines: constant (low, medium and high irrigation) and dynamic (early/late season water deficit). The following parameters were measured: trunk diameter, annual ring width and area, vessel diameter, specific hydraulic conductivity and stem water potential.\n\nHigh water availability early in the season (high irrigation and late deficit) resulted in vigorous vegetative growth (greater trunk diameter, ring width and area), wider vessels and increased specific hydraulic conductivity. The distribution of large xylem vessels was altered by drought stress, where high water availability early in the season caused a shift of the vessel population towards the wider frequency classes. Interestingly, the early deficit vines showed more negative water potential values late in the season compared to the low irrigation vines. This may imply an effect of anatomical structure on vine water status.\n\nHighlightsWater availability early in the season determines vegetative growth and stem anatomical structure in mature Vitis vinifera vines.

plant biology↗