Phospholipase Dα1 mediates the high-Mg 2 + stress response partially through regulation of K + homeostasis

Intracellular levels of Mg are tightly regulated, as Mg deficiency or excess affects normal plant growth and development. In Arabidopsis, we determined that phospholipase Dα1 (PLDα1) is involved in the stress response to high-magnesium conditions. The T-DNA insertion mutant pldα1 is hypersensitive to increased concentrations of magnesium, exhibiting reduced primary root length and fresh weight. PLDα1 activity increases rapidly after high-Mg treatment, and this increase was found to be dose dependent. Two lines harbouring mutations in the HKD motif, which is essential for PLDα1 activity, displayed the same high-Mg hypersensitivity of pldα1 plants. Moreover, we show that high concentrations of Mg disrupt K homeostasis, and that transcription of K homeostasis-related genes CIPK9 and HAK5 is impaired in pldα1. Additionally, we found that the akt1, hak5 double mutant is hypersensitive to high-Mg . We conclude that in Arabidopsis, the enzyme activity of PLDα1 is vital in the response to high-Mg conditions, and that PLDα1 mediates this response partially through regulation of K homeostasis.