Calcineurin B-like Protein CBL10 Directly Interacts with TOC34 (Translocon of the Outer Membrane of the Chloroplasts) and Decreases Its GTPase Activity in Arabidopsis

Abstract

As calcium sensor relays in plants, calcineurin B-like (CBL) proteins provide an important contribution to decoding Ca2+ signatures elicited by a variety of abiotic stresses. Currently, it is well known that CBLs perceive and transmit the Ca2+ signals mainly to a group of serine/threonine protein kinases called CBL-interacting protein kinases (CIPKs). In this study, we report that the CBL10 member of this family has a novel interaction partner besides the CIPK proteins. Yeast two-hybrid screening with CBL10 as bait identified an Arabidopsis cDNA clone encoding a TOC34 protein, which is a member of the TOC (Translocon of the Outer membrane of the Chloroplasts) complex and possesses the GTPase activity. Further analyses showed that in addition to CBL10, CBL7 also interacts with TOC34 at much lower strength in the yeast two-hybrid system. However, the rest of the CBL family members failed to interact with TOC34. Bimolecular fluorescence complementation (BiFC) analysis verified that the CBL10-TOC34 interaction occurs at the outer membrane of chloroplasts in vivo. In addition, we also demonstrated that CBL10 physically associates with TOC34 in vitro, resulting in a significant decrease in the GTPase activity of the TOC34 protein. Taken together, our findings clearly indicate that a member of the CBL family, CBL10, can modulate not only the CIPK members but also TOC34, allowing the CBL family to relay the Ca2+ signals in more diverse ways than currently known.

Calcineurin B-Like Proteins CBL4 and CBL10 Mediate Two Independent Salt Tolerance Pathways in Arabidopsis

“…Considering the fact that a proportion of the CBL10 protein was also localized to the dynamic endosomal compartments [16], NHX5/6 could also act as the candidate targets of the CBL10-CIPK complexes. In a recent work, translocon of the outer membrane of the chloroplasts 34 (TOC34) was identified as a novel interaction partner protein of CBL10 at the outer membrane of chloroplasts, clearly indicating that CBL10 can relay Ca 2+ signals in more diverse ways than currently known [40]. Identification of target transporter(s) directly regulated by the CBL10-CIPK module is an important and challenging task for future research, which would also unravel the pathway through which Na + is deposited into the plant vacuole.…”

Adaptation of Plants to Salt Stress: Characterization of Na+ and K+ Transporters and Role of CBL Gene Family in Regulating Salt Stress Response

“…Yeast two-hybrid screening with CBL10 as bait identified an Arabidopsis cDNA clone encoding a TOC34 protein, which is a member of the translocon of the outer membrane of chloroplasts (TOC) complex and possesses the GTPase activity. Bimolecular fluorescence complementation (BiFC) analysis verified that the CBL10-TOC34 interaction takes place at the outer membrane of chloroplasts in vivo and thus decreases its GTPase activity in Arabidopsis [188].…”

“…interaction takes place at the outer membrane of chloroplasts in vivo and thus decreases its GTPase activity in Arabidopsis [188].…”

Phylogenetic Diversity and Physiological Roles of Plant Monovalent Cation/H+ Antiporters

“…Also, CBL10 could participate in a vacuolar Na + homeostasis and interact with other protein kinases ( Kim et al., 2007 ; Waadt et al., 2008 ). Direct interaction with TOC34 translocon at the outer envelope membrane of chloroplasts 34) allows CBL10 to modulate Ca 2+ signals in diverse ways ( Cho et al., 2016 ). In addition, salt stress-induced SOS1A/SOS2 complex interacts, phosphorylates and activates PUT3 polyamine transporter ( Chai et al., 2020 ), leading to accumulation of polyamine in the cytosol and protecting cells from oxidative stress ( Shen et al., 2016 ).…”