Arabidopsis ECERIFERUM3 (CER3) Functions to Maintain Hydration for Pollen–Stigma Recognition During Fertilization

Plant stigmas distinguish the pollen grains and allow compatible ones to fertilize female gametes. To analyze the underlying mechanism, conditional male-sterile mutations with impaired pollen coat and pollen–stigma recognition were isolated. The mutant pollen could germinate in vitro but not in vivo, suggesting that they are viable. The mutant stigma cells that contacted their own pollen-generated callose, a carbohydrate typically produced in response to foreign pollen. The defects of pollen hydration and fertilization in the mutants were rescued by high humidity, indicating that hydration is required for pollen–stigma interaction. Pollination with mixture of wild type and mutant pollens demonstrated that the pollen–stigma recognition of mutant pollen was disrupted. The mutant plants exhibited lack of stem waxes and postgenital fusion between aerial floral organs. In addition, the mutant pollen was deficient in very-long-chain lipids and had excess tryphine. Transmission electron microscopy analysis showed that mutant pollen had almost the same surface structure as the wild type at bicellular pollen stage. However, abnormal plastoglobuli were observed in the plastids of the mutant tapetum, which was an indicative of altered lipid accumulation. CER3 transcripts were found in anther tapetum and microspores at development stage 9. Our data reveal that CER3 is required for biosynthesis of tryphine lipids which function to maintain hydration for pollen–stigma recognition during fertilization.