PHT4 foszfát-transzporterek jellemzése zöldalgában

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Phosphorus is essential for living organisms. It is found in all parts of the plant cell, is a structural component of nucleic acids and phospholipids, and is essential in signaling and energy transfer reactions, as well as in photosynthesis. Members of the PHT family are the best studied phosphate transporters in vascular plants. They are well known for their role in inorganic phosphate uptake from the soil and transport within the plant. Phosphate transport has been less studied in green algae, and surprisingly, no inorganic phosphate transporters have yet been characterized. In this thesis, we performed a detailed physiological characterization of two phosphate transporters found in the green alga Chlamydomonas reinhardtii. We have established that CrPHT4-7 and CrPHT4-3, members of the PHT4 family in C. reinhardtii, are inorganic phosphate transporters localized to the chloroplast envelope membrane. Based on a detailed physiological characterization, we concluded that CrPHT4-7 and CrPHT4-3 play a crucial role in maintaining an adequate level of inorganic phosphate in the chloroplast, thereby enhancing cellular fitness. Although CrPHT4-7 and CrPHT4-3 exhibit a relatively high degree of similarity with AtPHT4;4, they did not show substantial ascorbate transport activity in the physiologically relevant concentration range. We have shown that overexpressing CrPHT4-7 or CrPHT4-3 enhanced high light tolerance. On the other hand, the loss of CrPHT4-7 and CrPHT4-3 functions was not lethal. At the same time, the stress tolerance of pht4-3 pht4-7 double mutants was dramatically reduced, so it seems likely that the CrPHT4-7 and CrPHT4-3 transporters play a key role in transporting phosphate into the chloroplast. Summarizing our results, we can state that we succeeded in identifying and characterizing two phosphate transporters in the green alga C. reinhardtii. The results obtained during the detailed physiological characterization show that these transporters play an important role in maintaining the appropriate inorganic phosphate level of the chloroplast, thus improving the viability of the cells.

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