Tip‐localized Ca²⁺‐permeable channels control pollen tube growth via kinase‐dependent R‐ and S‐type anion channel regulation

Summary Pollen tubes ( PT s) are characterized by having tip‐focused cytosolic calcium ion (Ca 2+ ) concentration ([Ca 2+ ] cyt ) gradients, which are believed to control PT growth. However, the mechanisms by which the apical [Ca 2+ ] cyt orchestrates PT growth are not well understood. Here, we aimed to identify these mechanisms by combining reverse genetics, cell biology, electrophysiology, and live‐cell Ca 2+ and anion imaging. We triggered Ca 2+ ‐channel activation by applying hyperpolarizing voltage pulses and observed that the evoked [Ca 2+ ] cyt increases were paralleled by high anion channel activity and a decrease in the cytosolic anion concentration at the PT tip. We confirmed a functional correlation between these patterns by showing that inhibition of Ca 2+ ‐permeable channels eliminated the [Ca 2+ ] cyt increase, resulting in the abrogation of anion channel activity via Ca 2+ ‐dependent protein kinases ( CPK s). Functional characterization of CPK and anion‐channel mutants revealed a CPK 2/20/6‐dependent activation of SLAH 3 and ALMT 12/13/14 anion channels. The impaired growth phenotypes of anion channel and CPK mutants support the physiological significance of a kinase‐ and Ca 2+ ‐dependent pathway to control PT growth via anion channel activation. Other than unveiling this functional link, our membrane hyperpolarization method allows for unprecedented manipulation of the [Ca 2+ ] cyt gradient or oscillations in the PT tips and opens an array of opportunities for channel screenings.