PbrSYP71 regulates ER accumulation by interacting with actin during pollen tube growth in Pyrus

The uneven distribution of endoplasmic reticulum (ER) underlies the rapid polar growth of pollen tubes. However, the mechanism governing ER distribution remains elusive. In this study, we have identified a pollen tube-specific syntaxin protein, PbrSYP71. Our findings reveal that both overexpression and knocking down of PbrSYP71 inhibited pollen tube growth. Subcellular localization analysis demonstrates that PbrSYP71 anchors to the ER via its transmembrane structure. Overexpression of PbrSYP71 leads to clustered ER distribution in the pollen tube, while knocking down of PbrSYP71 abolishes the uneven ER distribution. Remarkably, transient overexpression of PbrSYP71{Delta}ABD, lacking the actin binding domain (ABD) of PbrSYP71, has no impact on ER distribution or pollen tube growth. Further investigation indicates that ABD is positioned on F-actin in the pollen tube and has a direct interaction with F-actin. PbrSYP71 assists the ER in moving towards the apex of pollen tube, with ABD displaying autonomous mobility. Our study elucidates that PbrSYP71 maintains uneven distribution of the ER by tethering ER to F-actin, facilitating ER movement towards the pollen tube apex for pear pollen tube elongation. These insights shed light on the mechanisms governing ER distribution in polarized cell growth.