XVI International Botanical Congess

When Chlamydomonas is starved for phosphorus it stops dividing, exhibits altered metabolic activities, synthesizes extracellular phosphatases and increases its capacity to take up Pi. We have isolated mutants unable to properly acclimate to phosphorus limitation. One mutant, psr1, is abnormal for several phosphorus starvation responses. Complementation of this mutant led to the isolation of the PSR1 gene, which encodes a putative transcription factor. The PSR1 protein is localized to the nucleus and increases in abundance during phosphorus limitation. These results will be discussed in the general context of nutrient limitation responses in photosynthetic organisms.