Chlamydomonas reinhardtii Mutants Abnormal in Their Responses to Phosphorus Deprivation1

Abstract

P-starved plants scavenge inorganic phosphate (Pi) by developing elevated rates of Pi uptake, synthesizing extracellular phosphatases, and secreting organic acids. To elucidate mechanisms controlling these acclimation responses in photosynthetic organisms, we characterized the responses of the green alga Chlamydomonas reinhardtii to P starvation and developed screens for isolating mutants (designated psr [phosphorus-stress response]) abnormal in their responses to environmental levels of Pi. The psr1-1 mutant was identified in a selection for cells that survived exposure to high concentrations of radioactive Pi. psr1-2 and psr2 were isolated as strains with aberrant levels of extracellular phosphatase activity during P-deficient or nutrient-replete growth. The psr1-1 and psr1-2 mutants were phenotypically similar, and the lesions in these strains were recessive and allelic. They exhibited no increase in extracellular phosphatase activity or Pi uptake upon starvation. Furthermore, when placed in medium devoid of P, the psr1 strains lost photosynthetic O 2 evolution and stopped growing more rapidly than wild-type cells; they may not be as efficient as wild-type cells at scavenging/accessing P stores. In contrast, psr2 showed elevated extracellular phosphatase activity during growth in nutrient-replete medium, and the mutation was dominant. The mutant phenotypes and the roles of Psr1 and Psr2 in P-limitation responses are discussed.

Lack of the Rhesus protein Rh1 impairs growth of the green alga Chlamydomonas reinhardtii at high CO 2

“…Plasmid pJES1459 linearized with EcoRV ( Fig. 1) was transformed into strain 4Aϩ by electroporation (30). The same was done for the vector NE451.…”

The Cia5 gene controls formation of the carbon concentrating mechanism in Chlamydomonas reinhardtii

“…Recipient cells were resuspended at a cell density of 4 ϫ 10 8 cells͞ml in 250 l TAP medium containing 60 mM sucrose and electroporated with cosmid DNA under conditions (25 F, 1875 V͞cm) described by Shimogawara et al (10). Transformed cells were allowed to recover in 50 ml TAP medium containing 60 mM sucrose for 24 h in the light with shaking.…”

Phosphorylation of Transitory Starch Is Increased during Degradation

“…Cells were grown photoautotrophically under a 12-h light period. Twenty-eight hours before the start of the labeling experiment, cells were transferred to a medium lacking phosphate to induce the high affinity phosphate uptake system (Shimogawara et al, 1999). Under these conditions, the photosynthetic capacity is not significantly affected (Wykoff et al, 1998).…”