Abstract
With the notable exception of angiosperms, all phototrophs contain different sets of flavodiiron proteins that help to relieve the excess of excitation energy on the photosynthetic electron transport chain during adverse environmental conditions, presumably by reducing oxygen directly to water. Among them, the Flv2-Flv4 dimer is only found in β-cyanobacteria and induced by high light, supporting a role in stress protection. The possibility of a similar protective function in plants was assayed by expressing Synechocystis Flv2-Flv4 in chloroplasts of tobacco and Arabidopsis. Flv-expressing plants exhibited increased tolerance toward high irradiation, salinity, oxidants, and drought. Stress tolerance was reflected by better growth, preservation of photosynthetic activity, and membrane integrity. Metabolic profiling under drought showed enhanced accumulation of soluble sugars and amino acids in transgenic Arabidopsis and a remarkable shift of sucrose into starch, in line with metabolic responses of drought-tolerant genotypes. Our results indicate that the Flv2-Flv4 complex retains its stress protection activities when expressed in chloroplasts of angiosperm species by acting as an additional electron sink. The flv2-flv4 genes constitute a novel biotechnological tool to generate plants with increased tolerance to agronomically relevant stress conditions that represent a significant productivity constraint.
Highlights
Oxygenic photosynthesis requires defined conditions of light and nutrient availability to operate at optimal efficiency, but phototrophic organisms, from cyanobacteria to higher plants, live and thrive in changing environments in which light intensity, temperature, and nutrient supply fluctuate widely during various timeframes
The photosynthetic electron transport chain (PETC) becomes over-reduced and the excess of energy and reducing power can be delivered to O2, increasing the production of reactive oxygen species (ROS) such as the superoxide anion radical, peroxides, and singlet O2, which further compromise the functionality of the photosynthetic machinery [1,2]
Most relevant among them are alternative electron transport (AET) pathways that dissipate the surplus of excitation energy and reducing equivalents, protecting photosynthesis from oxidative damage [3,4]
Summary
Oxygenic photosynthesis requires defined conditions of light and nutrient availability to operate at optimal efficiency, but phototrophic organisms, from cyanobacteria to higher plants, live and thrive in changing environments in which light intensity, temperature, and nutrient supply fluctuate widely during various timeframes. Dissipative systems involved in tolerance to environmental stresses include photosystem (PS) I-associated cyclic electron transport (CET); the Mehler–Asada pathway, termed pseudo-CET, which involves O2 reduction with transient ROS formation, chlororespiration, and non-photochemical quenching (NPQ) that dissipates the excess of excitation energy as heat; and photorespiration in C3 plants [3,4,5]. The function of Sll0218 in energy transfer from the prokaryotic antennae to PSII reaction centers is most likely restricted to cyanobacteria, but the activity of Flv2-Flv as an electron sink might be operative in other photosynthetic organisms lacking phycobilisomes, such as plants. The Flv2-Flv dimer played a critical role in relieving over-reduction of the PETC under stress conditions when expressed in plant chloroplasts
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
