IRONCROP: Flavodiiron proteins to rethink photosynthesis and boost crop yield 

Photosynthetic organisms are the primary producers supporting almost all life forms on our planet and are essential sources of oxygen, food, energy and materials for humans. The metabolism of photosynthetic organisms is supported by sunlight harvesting that fuels an electron transport, ultimately driving the synthesis of ATP and reducing equivalents (e.g. NADPH). Being exposed to highly dynamic environmental conditions, photosynthetic organisms need to continuously modulate energy collection and the flow of electrons in the photosynthetic apparatus to avoid the formation of toxic reactive species. Flavodiiron (FLV) proteins are seminal components of this regulatory machinery in cyanobacteria, eukaryotic green algae, non-vascular plants and gymnosperms while there were lost during the evolution of Angiosperms. In the moss Physcomitrium patens FLV proteins work as an important electron sink downstream of Photosystem I, acting as a safety valve from excess electrons in conditions of fluctuating light and protecting from photodamage. The absence of FLV has a major negative impact on P. patens growth, while Angiosperms can cope with the excess of photons by activating other mechanisms such as cyclic electron pathways and photorespiration. This opens the way to the possibility that FLV introduction in crops by genetic engineering can drive a positive effect on plant productivity. IRONCROP will contribute to the understanding of the FLV mechanisms by investigating specific questions at UNIPD and UNITO. First, the study of the FLV protein structure and biochemical properties in vitro will clarify its mechanism of activity and regulation. Then, the generation and characterization of P. patens plants with different levels of FLV, eventually also carrying specific mutations, will clarify its impact on the regulation of photosynthesis, plant metabolism and growth in vivo. FLV heterologous expression in a crop plant (tomato) will allow assessing its impact on growth and development in Angiosperms, also exploring the possibility of using this protein to improve plant productivity. FLV impact on the photosynthetic capacity will be punctually analyzed by a biophysical approach and extended by a biochemical quantification of the main molecules involved in functional photosynthesis (ATP. NADPH) and in stress response (ROS, Lipid peroxides, 2-phosphoglycolate, apocarotenoids). Stress response and retrograde signaling in Physcomitrium will be further characterized by studying the expression of marker genes for cellular detoxification (SCL14 homologues) under fluctuating light and after treatment with known signals (beta cyclocitral).