Arabidopsis pollen tube germination and growth depend on the mitochondrial calcium uniporter complex

Summary The mitochondrial calcium uniporter complex ( MCU c) was recently characterized in details in metazoans and consists of pore‐forming units ( MCUs ) and regulatory factors that channel calcium (Ca 2+ ) ion into the mitochondria. MCU s participate in many stress and developmentally related processes involving Ca 2+ . Although multiple homologues of MCU s and one regulatory subunit are usually present in plants, the first functional characterization and contribution to Ca 2+ related processes of these proteins have been reported recently. Here, we focused on two predicted Arabidopsis MCU s and studied their role in the germination and the growth of pollen tube, a tip‐growing cell type highly dependent on Ca 2+ homeostasis. Heterologous expression of MCU 1 or MCU 2 in yeast is sufficient to generate a mitochondrial Ca 2+ influx. MCU 1 and MCU 2 fluorescent reporters are co‐expressed in the vegetative cell mitochondria of the pollen grain but are undetectable in the embryo sac. We demonstrate that MCU 1 and MCU 2 can form a heterotypic complex. Phenotypic analyses revealed an impaired pollen tube germination and growth in vitro only for the mcu2 mutants suggesting a predominant role of MCU 2. Our results show that mitochondrial Ca 2+ controlled by MCU s is an additional player in Arabidopsis pollen tube germination and growth.