Arabidopsis VAC14 Is Critical for Pollen Development through Mediating Vacuolar Organization

Pollen viability depends on dynamic vacuolar changes during pollen development involving increases and decreases of vacuolar volume through water and osmolite accumulation and vacuolar fission. Mutations in FAB1A to FAB1D, the genes encoding phosphatidylinositol 3,5-bisphosphate [PI(3,5)P₂]-converting kinases, are male gametophyte lethal in Arabidopsis (Arabidopsis thaliana) due to defective vacuolar fission after pollen mitosis I, suggesting a key role of the phospholipid in dynamic vacuolar organization. However, other genetic components that regulate the production of PI(3,5)P₂ and its involvement in pollen germination and tube growth are unknown. Here, we identified and characterized Arabidopsis VAC14, a homolog of the yeast and metazoan VAC14s that are crucial for the production of PI(3,5)P₂VAC14 is constitutively expressed and highly present in developing pollen. Loss of function of VAC14 was male gametophyte lethal due to defective pollen development. Ultrastructural studies showed that vacuolar fission after pollen mitosis I was compromised in vac14 mutant microspores, which led to pollen abortion. We further showed that inhibiting the production of PI(3,5)P₂ or exogenous application of PI(3,5)P₂ mimicked or rescued the pollen developmental defect of the vac14 mutant, respectively. Genetic interference and pharmacological approaches suggested a role of PI(3,5)P₂ in pollen germination and tube growth. Our results provide insights into the function of VAC14 and, by inference, that of PI(3,5)P₂ in plant cells.