The Role of Sec15b and Phosphatidylinositol-4-Phosphate in Early Compatible Pollen-pistil Interactions

Stigmas of Arabidopsis thaliana carrying the exo70A1-1 mutation are defective in early pollen-pistil interactions; pollen grain adhesion to the stigma, pollen hydration, and penetration of the stigmatic surface by the pollen tube. Exo70 function in directed secretion has been linked to its ability to bind the phosphatidylinositides. To provide support that the classical, octomeric exocyst complex, which contains the Exo70 subunit, participates in compatible pollen-pistil interactions, this process was analyzed in plants deficient in Sec15, another subunit of the exocyst. Additionally, the role of phosphatidylinositol-4-phosphate (PI-4-P) in female fertility was evaluated through the use of the mutants ROOT HAIR DEFECTIVE 4-1 and PI4Kβ1β2 -/-, which have increased and decreased levels of PI-4-P respectively. Reduction of Sec15b levels or perturbation of PI-4-P in the stigma resulted in a reduced ability of of the transgenic/mutant stigmas to support pollen grain hydration; though all other stages of early pollen pistil interactions were unaffected.MAS