IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Recovering the cyanobacterial heritage in land plants: the case of flavodoxin
Autor/es:
TOGNETTI V; ZURBRIGGEN M; VALLE E; CARRILLO N; MORANDI E; MELZER M; HAJIREZAEI MR; FILLAT M
Lugar:
Jaca, España.
Reunión:
Simposio; XVI International Symposium on Flavins and Flavoproteins; 2008
Resumen:
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.