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

Intracellular levels of Mg(2+)are tightly regulated, as Mg(2+)deficiency or excess affects normal plant growth and development. In Arabidopsis, we determined that phospholipase D alpha 1 (PLD alpha 1) is involved in the stress response to high-magnesium conditions. The T-DNA insertion mutantpld alpha 1is hypersensitive to increased concentrations of magnesium, exhibiting reduced primary root length and fresh weight. PLD alpha 1 activity increases rapidly after high-Mg(2+)treatment, and this increase was found to be dose dependent. Two lines harbouring mutations in the HKD motif, which is essential for PLD alpha 1 activity, displayed the same high-Mg(2+)hypersensitivity ofpld alpha 1plants. Moreover, we show that high concentrations of Mg(2+)disrupt K(+)homeostasis, and that transcription of K(+)homeostasis-related genesCIPK9andHAK5is impaired inpld alpha 1. Additionally, we found that theakt1, hak5double mutant is hypersensitive to high-Mg2+. We conclude that in Arabidopsis, the enzyme activity of PLD alpha 1 is vital in the response to high-Mg(2+)conditions, and that PLD alpha 1 mediates this response partially through regulation of K(+)homeostasis.