Psr1, a nuclear localized protein that regulates phosphorus metabolism in Chlamydomonas

Understanding the ways in which phosphorus metabolism is regulated in photo synthetic eukaryotes is critical for optimizing crop productivity and manag ing aquatic ecosystems in which phosphorus can be a major source of polluti on. Here we describe a gene encoding a regulator of phosphorus metabolism, designated Psr1 (phosphorus starvation response), from a photosynthetic euk aryote. The Psr1 protein is critical for acclimation of the unicellular gre en alga Chlamydomonas reinhardtii to phosphorus starvation. The N-terminal half of Psr1 contains a region similar to myb DNA-binding domains and the C -terminal half possesses glutamine-rich sequences characteristic of transcr iptional activators. The level of Psr1 increases at least 10-fold upon phos phate starvation, and immunocytochemical studies demonstrate that this prot ein is nuclear-localized under both nutrient-replete and phosphorus-starvat ion conditions. Finally, Psr1 and angiosperm proteins have domains that are similar, suggesting a possible role for Psr1 homologs in the control of ph osphorus metabolism in vascular plants. With the identification of regulato rs such as Psr1 it may become possible to engineer photosynthetic organisms for more efficient utilization of phosphorus and to establish better pract ices for the management of agricultural lands and natural ecosystems.