Actin depolymerizing factors ADF7 and ADF10 play distinct roles during pollen development and pollen tube growth

Abstract

An important player in actin remodeling is the actin depolymerizing factor (ADF) which increases actin filament treadmilling rates. Previously, we had prepared fluorescent protein fusions of two Arabidopsis pollen specific ADFs, ADF7 and ADF10. These had enabled us to determine the temporal expression patterns and subcellular localization of these proteins during male gametophyte development. Here we generated stable transformants containing both chimeric genes allowing for simultaneous imaging and direct comparison. One of the striking differences between the two proteins was the localization profile in the growing pollen tube apex. Whereas ADF10 was associated with the filamentous actin array forming the subapical actin fringe, ADF7 was present in the same cytoplasmic region, but in diffuse form. This suggests that ADF7 is involved in the high actin turnover that is likely to occur in the fringe by continuously and efficiently depolymerizing filamentous actin and supplying monomeric actin to the advancing end of the fringe. The possibility to visualize both of these pollen-specific ADFs simultaneously opens avenues for future research into the regulatory function of actin binding proteins in pollen.

Figure 1. Subcellular localization of Arabidopsis ADF7 and ADF10 in hydrated pollen grains (A–C), short (D–F) and long pollen tubes (G,H and I). Micrographs (A,B,D,E,G and H) are maximum projections of Z-stacks acquired with a Zeiss LSM 510 META/LSM 5 LIVE/Axiovert 200M system confocal microscope using a two channel function. ADF7-CFP imaging was performed with a 458 nm laser and ADF10-YFP fluorescence was excited with a 488 nm argon laser. Micrographs in (C,F and I) are merged images of the corresponding ADF7 (red) and ADF10 (green) micrographs. Yellow indicates colocalization. Images are shown in false color. Scale bars = 10 µm.