Gene structure and expression pattern analysis of three monodehydroascorbate reductase (Mdhar) genes in Physcomitrella patens: Implications for the evolution of the MDHAR family in plants

The original publication can be found at www.springerlink.comThe ascorbate–glutathione pathway plays a major role in the detoxification of reactive oxygen species (ROS) in vascular plants. One of the key enzymes in this pathway is monodehydroascorbate reductase (MDHAR), a FAD enzyme that catalyses the reduction of the monodehydroascorbate radical. To elucidate the evolution and functional role of MDHAR we identified and characterised MDHARs from the moss Physcomitrella patens. Expressed sequence tag (EST) databases containing approximately 100.000 ESTs from Physcomitrella were searched and three isoforms of monodehydroascorbate reductase (PpMDHAR1, PpMDHAR2 and PpMDHAR3) were identified. In vascular plants MDHAR is found in the cytosol, chloroplast, mitochondria and peroxisome. Surprisingly, all three PpMDHARs resembled the cytosolic isoforms from vascular plants lacking the NH ₂-terminal or COOH-terminal extension found in organelle targeted MDHARs. The number and position of introns was also conserved between PpMDHARs and cytosolic MDHARs from vascular plants. Phylogenetic analysis revealed that cytosolic MDHARs are monophyletic in origin and the ancestral gene evolved before the divergence of bryophytes more than 400 million years ago. Transcript analyses showed that expression of PpMdhar1 and PpMdhar3 was increased up to 5-fold under salt stress, osmotic stress or upon exposure to abscisic acid. In contrast, PpMdhar transcription levels were unchanged upon chilling, UV-B exposure or oxidative stress. The conservation of cytosolic MDHAR in the land-plant lineage and the transcriptional upregulation under water deficiency suggest that the evolution of cytosolic MDHAR played an essential role in stress protection for land plants when they inhabited the dry terrestrial environment.Christina Lunde, Ute Baumann, Neil J. Shirley, Damian P. Drew and Geoffrey B. Finche

Measurement of single-diffractive dijet production in proton–proton collisions at √s=8Te with the CMS and TOTEM experiments

Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss ξ and the four-momentum transfer squared t. Both processes pp→pX and pp→Xp, i.e. with the proton scattering to either side of the interaction point, are measured, where X includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton–proton collisions at s=8Te during a dedicated run with β∗=90m at low instantaneous luminosity and correspond to an integrated luminosity of 37.5nb-1. The single-diffractive dijet cross section σjjpX, in the kinematic region ξ< 0.1 , 0.03<|t|<1Ge2, with at least two jets with transverse momentum pT>40Ge, and pseudorapidity | η| < 4.4 , is 21.7±0.9(stat)-3.3+3.0(syst)±0.9(lumi)nb. The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of ξ, is presented as a function of x, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for x values in the range - 2.9 ≤ log 10x≤ - 1.6 , is R=(σjjpX/Δξ)/σjj=0.025±0.001(stat)±0.003(syst), where σjjpX and σjj are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons. © 2020, CERN for the benefit of the CMS and TOTEM collaborations