The Role Of CER3 In The Formation And Hydration Of Arabidopsis Pollen Surface

Plants discriminate among the pollen grains that land on their stigma,allowing only compatible pollen to fertilize female gametes.To analyze these cell-cell interactions,conditional male-sterile mutations that disrupt pollen-stigma recognition by altering the pollen coat were isolated and described here.Stigma cells that contact the mutant pollen produce callose,a carbohydrate produced in response to foreign pollen.The mutant pollen fails to germinate because it does not hydrate on the stigma,yet germinates in vitro,suggesting it is viable.High humidity restores pollen hydration leading to successful fertilization.Results from mixed pollination experiments suggest that the mutant pollen grains specifically lack a functional pollen-stigma recognition system.The sterile plants also lack stem waxes and display postgenital fusion between aerial floral organs.Analysis of mutant pollen indicated that it is deficient in long-chain lipids and has excess tryphine normally present on its surface.Transmission electron microscopy observation showed that mutant pollen grains have 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 indicative of altered lipid accumulation.In situ hybridization experiment showed that CER3 was strongly expressed in stage 9 anther tapetum and microspores.Further analysis indicated that CER3 protein was localized to the cell plasma membrane.These results demonstrate that CER3 is involved in biosynthesis and/or transport of tryphine lipids and suggest that tryphine lipids are required for fertilization through directly signaling the stigma.