Conditional identification of phosphate-starvation-response mutants in Arabidopsis thaliana

Plants have evolved elaborate metabolic and developmental adaptations to lo w phosphorus availability. Biochemical responses to phosphate limitation in clude increased production and secretion of phosphate-acquisition proteins such as nucleases, acid phosphatases, and high-affinity phosphate transport ers. However, the signal transduction pathways that sense phosphate availab ility and integrate the phosphate-starvation response in plants are unknown . We have devised a screen for conditional mutants in Arabidopsis thaliana (L.) Heynh. to dissect signaling of phosphate limitation. Our genetic scree n is based on the facultative ability of wild-type Arabidopsis plants to me tabolize exogenous DNA when inorganic phosphate is limiting. After screenin g 50,000 M2 seedlings, we isolated 22 confirmed mutant lines that showed se verely impaired growth on medium containing DNA as the only source of phosp horus, but which recovered on medium containing soluble inorganic phosphate . Characterization of nine such mutant lines demonstrated an inability to u tilize either DNA or RNA. One mutant line, psr1 ((p) under bar hosphate (s) under bar tarvation (r) under bar esponse), had significantly reduced acti vities of phosphate-starvation-inducible isoforms of ribonuclease and acid phosphatase under phosphate-limiting conditions. The data suggest that a su bset of the selected mutations impairs the expression of more than one phos phate-starvation-inducible enzyme required for utilization of exogenous nuc leic acids, and may thus affect regulatory components of a Pi starvation re sponse pathway in higher plants.