CONICET | Buscador de Institutos y Recursos Humanos

Photosynthetic organisms growing under natural conditions face episodic situations of environmental stress in the course of their lifetimes. Drought, chilling, over-irradiation, nutritional deficit (i. e., iron deprivation), etc., represent the major factor affecting crop yield and decline of natural forests. Most of the damage is caused by perturbation of electron delivery, resulting in adventitious transfer to oxygen and concomitant build-up of partially reduced oxygen species that react with and inactivate all types of biomolecules. Plants, and the microorganisms from which plants evolved (i. e., algae and cyanobacteria), display different strategies to survive under such adverse conditions. Plants resort to multi-level responses involving avoidance, scavenging, repair and optimization of nutrient and water uptake. Microorganisms, instead, display a unique and rapid response consisting in substitution of the most sensitive targets by functional counterparts, which are stress- resistant and allow them to thrive and reproduce under otherwise detrimental conditions. Most conspicuous among them is the induction in cyanobacteria and some oceanic algae of the electron shuttle flavoprotein flavodoxin (Fld) to take over the functions of the iron-sulphur protein ferredoxin (Fd), whose levels decline under iron deprivation and virtually all environmental adversities. Fld induction is considered as a major factor determining the ability to colonize iron-poor waters, and its relevance in the dynamics of marine ecology is underscored by its use by oceanographers as a proxy for iron limitation. Somewhere in the transition from green algae to terrestrial plants the Fld gene was lost from the plant genome and the adaptive advantages conferred by its expression and induction were irreversibly lost. Interestingly, plant enzymes whose prokaryotic ancestors used Fld as normal or occasional substrate were able to productively interact with the flavoprotein in vitro. We report herein that plant transformation with a bacterial Fld targeted to chloroplasts led to increased tolerance to a wide-range of environmental hardships from biotic, abiotic and xenobiotic origin, including water deficit, contact herbicides, extreme temperatures and radiations. Transgenic plants were also able to grow in iron-poor soils and media. In all cases, development of tolerance relied on the interaction of the foreign protein with endogenous electron-transfer pathways including photosynthesis, thioredoxin-mediated regulation, nitrogen assimilation and amino acid metabolism. The article also discusses the molecular bases of Fld recognition by plant enzymes after eons of evolutionary divergence, the reasons of its disappearance from the plant genome despite its obvious advantages, and the potential use of Fld as a biotechnological tool to develop stress-tolerant crops.