Photosynthetic characterization of flavodoxin-expressing tobacco plants reveals a high light acclimation-like phenotype

GÓMEZ, RODRIGO; CARRILLO, NÉSTOR; LODEYRO, ANABELLA F.; FIGUEROA, NICOLÁS

Roma

Congreso; International Congress on Biophysics of Photosynthesis: from molecules to the field; 2019

The photosynthetic electron transport contributes the energy and reducing power necessary for CO2 assimilation and central metabolic pathways in plants, algae and cyanobacteria. Even when the photosynthetic process is highly efficient, it is subjected to multiple environmental and developmental factors affecting its performance. Excess radiation and fluctuations in the quality and intensity of the light are some of the most important limitations to plant fitness under field conditions. Several protective and dissipative mechanisms are widely distributed between photosynthetic organism helping them to cope with harmful situations at different timescales. In addition, the redox status of various components of the photosynthetic electron transport chain (PETC) and of the chloroplast stroma provide signals that allow plants to adequately respond to developmental and environmental stimuli. In cyanobacteria and some oceanic algae, expression of the electron shuttle flavodoxin (Fld) is induced under various stresses as an adaptive response tothe decrease of ferredoxin (Fd) at the reducing side of photosystem (PS) I. Genes encoding Fld are absent from plant genomes, but transgenic tobacco plants expressing cyanobacterial Fld in chloroplasts showed increased tolerance towards several stressful conditions. In the present work we focused on the effect of Fld expression on photosynthetic performance under normal growth conditions, using transgenic tobacco lines accumulating Fd and Fld at similar levels in the stroma, which results in the introduction of a new player in the network of chloroplast electron distribution.Measurements of chlorophyll a fluorescence and spectroscopic determinations were carried out on wild-type (WT) and two independent lines expressing similar levels of plastid-targeted Fld. The results revealed that the presence of the flavoprotein led to higher PSII and PSI performance, increased plastoquinone pool oxidation state, modifications in pigment contents and a reduction in the PSII effective antenna size. These changes suggest that Fld effects extend beyond a simple alteration of electron flow partitioning. Interestingly enough, many of the changes introduced by Fld expression resemble the phenotype displayed by high light-adapted leaves, even though our plants were grown under low to moderate irradiation. Besides the advantages to plant fitness under field conditions, our results allowed us to propose the use of Fld expression in as a promising tool to study the complex relationship between stroma redox poise and general acclimation processes.