The pmr Gene, Encoding a Ca 2+ -ATPase, Is Required for Calcium and Manganese Homeostasis and Normal Development of Hyphae and Conidia in Neurospora crassa

Abstract

ABSTRACT The pmr gene is predicted to encode a Ca 2+ -ATPase in the secretory pathway. We examined two strains of Neurospora crassa that lacked PMR: the Δ pmr strain, in which pmr was completely deleted, and pmr RIP , in which the gene was extensively mutated. Both strains had identical, complex phenotypes. Compared to the wild type, these strains required high concentrations of calcium or manganese for optimal growth and had highly branched, slow-growing hyphae. They conidiated poorly, and the shape and size of the conidia were abnormal. Calcium accumulated in the Δ pmr strains to only 20% of the wild-type level. High concentrations of MnCl 2 (1 to 5 mM) in growth medium partially suppressed the morphological defects but did not alter the defect in calcium accumulation. The Δ pmr Δ nca-2 double mutant ( nca-2 encodes a Ca 2+ -ATPase in the plasma membrane) accumulated 8-fold more calcium than the wild type, and the morphology of the hyphae was more similar to that of wild-type hyphae. Previous experiments failed to show a function for nca-1 , which encodes a SERCA-type Ca 2+ -ATPase in the endoplasmic reticulum (B. J. Bowman, S. Abreu, E. Margolles-Clark, M. Draskovic, and E. J. Bowman, Eukaryot. Cell 10:654-661, 2011). The pmr RIP Δ nca-1 double mutant accumulated small amounts of calcium, like the Δ pmr strain, but exhibited even more extreme morphological defects. Thus, PMR can apparently replace NCA-1 in the endoplasmic reticulum, but NCA-1 cannot replace PMR. The morphological defects in the Δ pmr strain are likely caused, in part, by insufficient concentrations of calcium and manganese in the Golgi compartment; however, PMR is also needed to accumulate normal levels of calcium in the whole cell.