FtsZ1/FtsZ2 Turnover in Chloroplasts and the Role of ARC3.

Chloroplast division requires filamentation temperature-sensitive Z (FtsZ), a tubulin-like GTPase of cyanobacterial endosymbiotic origin. Plants and algae possess two distinct FtsZ protein families, FtsZ1 and FtsZ2 that co-assemble into a ring (Z-ring) at the division site. Z-ring assembly and disassembly and division site positioning is controlled by both positive and negative factors via their specific interactions with FtsZ1 and FtsZ2. Here we present the in planta analysis of Arabidopsis FtsZ1 and FtsZ2 turnover in the context of a native chloroplast division machinery. Fluorescence recovery after photobleaching analysis was conducted using fluorescently tagged FtsZ at wild-type (WT)-like levels. Rapid photobleaching, low signal-to-noise ratio, and phototropic movements of chloroplasts were overcome by (i) using progressive intervals in time-lapse imaging, (ii) analyzing epidermal rather than stromal chloroplasts, and (iii) employing image stack alignment during postprocessing. In plants of WT background, fluorescence recovery half-times averaged 117 and 325 s for FtsZ1 and FtsZ2, respectively. In plants lacking ARC3, the key negative regulator of FtsZ assembly, the turnover was threefold slower. The findings are discussed in the context of previous results conducted in a heterologous system.