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Pollen tube tip growth is an extreme form of polarized cell growth,which requires polarized exocytosis based on dynamic actin cytoskeleton.However,the molecular basis for the connection between actin filaments and exocytic vesicles is unclear.Here,we identified a Lilium longiflorum pollen-specific formin (LIFH1) and found it was involved in pollen tube tip growth.LIFH1 localized at the apical vesicles and plasma membrane via its N-terminus.Overexpression of LIFH1 induced excessive actin cables in the tube tip region,and downregulation of LIFH1 eliminated actin fringe.FRAP analysis revealed that LIFH1 labeled exocytic vesicles,which exhibited a clear initial accumulation at the shoulder of the apex.Meanwhile,we found that the exocytic site coincided with the leading edge of the actin fringe,indicating the correlation between actin fringe and exocytic vesicles.Time-lapse analysis of pollen tubes simultaneously expressing LIFH1-GFP and Lifeact-mRFP suggested that nascent actin filaments followed the emergence of the apical vesicles,implying that LIFH1 could initiate actin polymerization from the apical vesicles.In vitro biochemical assays showed that the FH1FH2 domain of LIFH1 could nucleate actin polymerization and bundle actin filaments.In addition,LIFH1 FH1FH2 could attach to the barbed end of actin filaments,and in the presence of lily profilin isoforms,LIFH1 FH1FH2 enhanced actin filament elongation rates.Thus,we propose that LIFH1 and profilins coordinates the interaction between actin fringe and exocytic vesicle trafficking,which provides a mechanism for the delivery of exocytic vesicles to the shoulder of the apex during the growth of lily pollen tubes.