Disruption of actin filaments induces mitochondrial Ca2+ release to the cytoplasm and [Ca2+]c changes in Arabidopsis root hairs

Abstract

BackgroundMitochondria are dynamic organelles that move along actin filaments, and serve as calcium stores in plant cells. The positioning and dynamics of mitochondria depend on membrane-cytoskeleton interactions, but it is not clear whether microfilament cytoskeleton has a direct effect on mitochondrial function and Ca2+ storage. Therefore, we designed a series of experiments to clarify the effects of actin filaments on mitochondrial Ca2+ storage, cytoplasmic Ca2+ concentration ([Ca2+]c), and the interaction between mitochondrial Ca2+ and cytoplasmic Ca2+ in Arabidopsis root hairs.ResultsIn this study, we found that treatments with latrunculin B (Lat-B) and jasplakinolide (Jas), which depolymerize and polymerize actin filaments respectively, decreased membrane potential and Ca2+ stores in the mitochondria of Arabidopsis root hairs. Simultaneously, these treatments induced an instantaneous increase of cytoplasmic Ca2+, followed by a continuous decrease. All of these effects were inhibited by pretreatment with cyclosporin A (Cs A), a representative blocker of the mitochondrial permeability transition pore (mPTP). Moreover, we found there was a Ca2+ concentration gradient in mitochondria from the tip to the base of the root hair, and this gradient could be disrupted by actin-acting drugs.ConclusionsBased on these results, we concluded that the disruption of actin filaments caused by Lat-B or Jas promoted irreversible opening of the mPTP, resulting in mitochondrial Ca2+ release into the cytoplasm, and consequent changes in [Ca2+]c. We suggest that normal polymerization and depolymerization of actin filaments are essential for mitochondrial Ca2+ storage in root hairs.

The Actin-Related Protein2/3 Complex Regulates Mitochondrial-Associated Calcium Signaling during Salt Stress inArabidopsis

“…The addition of FCCP decreased the TMRM fluorescence and restored the calcein emission (see Supplemental Figure 7 online). Consistent with previous reports (Petronilli et al, 1999(Petronilli et al, , 2001Wang et al, 2010), our results demonstrate that calcein emission can be restored by FCCP uncoupling agents that cause TMRM release from mitochondria.…”

“…mPTP opening was monitored using calcein/Co 2+ imaging (Petronilli et al, 1999;Petronilli et al, 2001;Wang et al, 2010), and MitoTracker Red CMXRos was used to confirm that calcein was localized to the mitochondria (see Supplemental Figure 6A online). Protoplasts of the wild type and arp2-2 were left untreated or treated with 150 mM NaCl for 10, 120, or 240 min.…”

“…One output of the SOS pathway is regulation of actin microfilament (MF) dynamics and stability (Wang et al, 2010;Zhou et al, 2010;Liu and Guo, 2011;Ye et al, 2013). MFs in both the sos2 and sos3 mutants have abnormal dynamics and depolymerize faster than in the wild type (Wang et al, 2010;Ye et al, 2013).…”

“…MFs in both the sos2 and sos3 mutants have abnormal dynamics and depolymerize faster than in the wild type (Wang et al, 2010;Ye et al, 2013). More recently, MF dynamics modulated by the Actin-Related Protein2 Arp2/3 complex were reported to regulate stomatal movement, and a change in calcium signaling was hypothesized to play a key role in this response .…”

The conserved mobility of mitochondria during leaf senescence reflects differential regulation of the cytoskeletal components inArabidopsis thaliana

“…However, we may also question whether the interaction actin-filaments/mitochondria could act as signaling agents regulating the death of cells notably by modulating Ca 2+ concentrations. 17 …”