MAPKs influence pollen-tube growth via phosphorylation of PIP5K6, affecting PtdIns(4,5)P2 formation

Pollen tubes exhibit unidirectional, polar growth because vesicles carrying compounds required for growth  are selectively transported to the growing apex. The phosphoinositide PtdIns(4,5)P2 accumulates at the apex and  is thought to help with vesicle targeting. Helpel et al. showed that the lipid kinase responsible for PtdIns(4,5)P2 production, PIP5K6, is phosphorylated by incubation with extracts from elongating pollen tubes. They identified MPK6 as a protein kinase that interacts with and phosphorylates PIP5K6, inhibiting its activity and interfering with PtdIns(4,5)P2 production and pollen tube elongation. The authors suggest that regulation of PtdIns(4,5)P2 production via MAPKs may help to control the directional growth of pollen tubes. (Summary by Mary Williams) Plant Cell 10.1105/tpc.17.00543