Suppression of reactive oxygen species accumulation in chloroplasts prevents leaf damage but not growth arrest in salt-stressed tobacco plants

Crop yield reduction due to salinity is a growing agronomical concern in many regions. Increased production of reactive oxygen species (ROS) in plant cells accompanies many abiotic stresses including salinity, acting as toxic and signaling molecules during plant stress responses. While ROS are generated in various cellular compartments, chloroplasts represent a main source in the light, and plastid ROS synthesis and/or elimination have been manipulated to improve stress tolerance. Transgenic tobacco plants expressing a plastid-targeted cyanobacterial flavodoxin, a flavoprotein that prevents ROS accumulation specifically in chloroplasts, displayed increased tolerance to many environmental stresses, including drought, excess irradiation, extreme temperatures and iron starvation. Surprisingly, flavodoxin expression failed to protect transgenic plants against NaCl toxicity. However, when high salt was directly applied to leaf discs, flavodoxin did increase tolerance, as reflected by preservation of chlorophylls, carotenoids and photosynthetic activities. Flavodoxin decreased salt-dependent ROS accumulation in leaf tissue from discs and whole plants, but this decline did not improve tolerance at the whole plant level. NaCl accumulation in roots, as well as increased osmotic pressure and salt-induced root damage, were not prevented by flavodoxin expression. The results indicate that ROS formed in chloroplasts have a marginal effect on plant responses during salt stress, and that sensitive targets are present in roots which are not protected by flavodoxin.Para citar este articulo: Lodeyro AF, Giró M, Poli HO, Bettucci G, Cortadi A, Ferri AM, et al. (2016) Suppression of Reactive Oxygen Species Accumulation in Chloroplasts Prevents Leaf Damage but Not Growth Arrest in Salt-Stressed Tobacco Plants. PLoS ONE 11(7): e0159588. doi:10.1371/journal.pone.0159588Fil: Lodeyro, Anabella F. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina.Fil: Giró, Mariana. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina.Fil: Poli, Hugo O. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina.Fil: Bettucci, Gabriel. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Departamento de Ciencias Biológicas; Argentina.Fil: Cortadi, Adriana. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Departamento de Ciencias Biológicas; Argentina.Fil: Ferri, Alejandro M. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Departamento de Química Analítica; Argentina.Fil: Carrillo, Néstor. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario (IBR -CONICET); Argentina

Identification of Xenologs and Their Characteristic Low Expression Levels in the Cyanobacterium Synechococcus elongatus

Horizontal gene transfer (HGT) is a central process in prokaryotic evolution. Once a gene is introduced into a genome by HGT, its contribution to the fitness of the recipient cell depends in part on its expression level. Here we show that in Synechococcus elongatus PCC 7942, xenologs derived from non-cyanobacterial sources exhibited lower expression levels than native genes in the genome. In accord with our observation, xenolog codon adaptation indexes also displayed relatively low expression values. These results are in agreement with previous reports that suggested the relative neutrality of most xenologs. However, we also demonstrated that some of the xenologs detected participated in cellular functions, including iron starvation acclimation and nitrate reduction, which corroborate the role of HGT in bacterial adaptation. For example, the expression levels of some of the xenologs detected are known to increase under iron-limiting conditions. We interpreted the overall pattern as an indication that there is a selection pressure against high expression levels of xenologs. However, when a xenolog protein product confers a selective advantage, natural selection can further modulate its expression level to meet the requirements of the recipient cell. In addition, we show that ORFans did not exhibit significantly lower expression levels than native genes in the genome, which suggested an origin other than xenology.This work was supported by the Consejo Nacional de Ciencia y Tecnología CONACYT CB-2010-01 (Grant Number 157220). This work was also funded by Grants from the Spanish Ministry of Economy and Competitiveness (SAF2009-13032-C02-01 and SAF2012-31187), from Generalitat Valenciana (Prometeo/2009/092; Spain), and from ST-FLOW (EU). Work in the FdlC laboratory was financed by the Spanish Ministry of Economy and Competitiveness (BFU2011-26608) and the European Seventh Framework Program (612146/FP7-ICT-2013-10 and 282004/FP7-HEALTH-2011-2.3.1-2).Peer Reviewe