Actins are among the most abundant and conserved proteins in eukaryotic cells, where they form filamentous structures that perform vital roles in key cellular processes. Although large amounts of data on the biochemical activities, dynamic behaviors, and important cellular functions of plant actin filaments have accumulated, their structural basis is elusive. Here, we report a 3.9 Å structure of the plant actin filament (ZMPA) from Zea mays pollen using cryo-electron microscopy. The structure shows a right-handed, double-stranded (two strands running parallel to each other) and staggered architecture that is stabilized by intra- and interstrand interactions. While the overall structure resembles that of other actin filaments, its DNase I-binding loop (D-loop) bends further outward, adopting an open conformation similar to that of the jasplakinolide- or Beryllium fluoride (BeF_x)-stabilized rabbit skeleton muscle actin (RSMA) filament. Single-molecule magnetic tweezer analysis revealed that the ZMPA filament can resist a greater stretching force than the RSMA filament. Overall, these data provide evidence that plant actin filaments have greater stability than animal actin filaments, which is important for their roles as tracks for long-distance vesicle and organelle transportation.

The structural data (Supplemental Movies 1 and 2) were from the structure of Zea mays pollen actin filaments that we determined by cryo-electron microscopy. These movies were made by Chimera software. The stretching data (Supplemental Movies 3, 4, 5 and 6) were from the single-molecular magnetic tweezer analysis of actin filaments in our study. These movies were made by Wondershare and MATLAB.