Ca2+ signalling in plant immune response: from pattern recognition receptors to Ca2+ decoding mechanismsIF:8

Endomembrane channels
A first wave of Ca2+ from the apoplast can trigger so-called Ca2+-induced Ca2+ release (CICR)from internal Ca2+ stores. In animals,binding of inositol trisphosphate (InsP3) to the InsP3-receptor inthe endoplasmic reticulum (ER) results in Ca2+ release into thecytosol (Missiaen et al., 1992). Such InsP3 receptor Ca2+ channelsseem to be missing in land plants, and with the vacuole constitutingthe largest potential Ca2+ store in plant cells, the tonoplasticchannels could be the major endomembrane channels mediatingCICR (Sch€onknecht, 2014). The two-pore-channel 1 (TPC1), a
slow-vacuolar (SV) cation channel, is the main candidate tonoplastchannel permeable to (and activated by) Ca2+ (Ward & Schroeder,1994). Predictive models, however, questioned TPC1’s suitabilityin CICR (Chen et al., 2012) and there is, in general, muchdisagreement on TPC1’s role as a Ca2+ channel (for a comprehensive debate, see the recent review by Sch€onknecht (2014)). One
dispute concerning TPC1 localization was recently resolved, whenit was shown that an N-terminal motif directs Arabidopsis TPC1 totonoplast (Larisch et al., 2012). While the rice TPC1 was reported
to be in plasma membranes (Hamada et al., 2012), recent evidencepoints to lysovacuolar localization for TPC1 from both monocotand dicot plants (Dadacz-Narloch et al., 2013), and even animalTPCs (Cang et al., 2014). If TPC1 is indeed the main tonoplastCa2+ channel, it remains unclear why loss of the singleton AtTPC1gene did not reveal any obvious Ca2+-regulated phenotypes in a
wide range of stress scenarios (Ranf et al., 2008). However, recentdata showed that a salt-inducedCa2+ wave from roots to shoots isabolished in the tpc1 mutant (Choi et al., 2014b). Thus, subtlephenotypes of tpc1 may be difficult to detect or are visible only in acell/tissue-specific manner.

感谢德国莱布尼茨植物生物化学研究所引用文献