Differential Modulation of Brassinosteroid and Ethylene Signalling Systems by Native and Constitutively Active Forms of the AtCPK1 Gene in Transgenic Tobacco Plants Under Heat Stress

Among other calcium decoders, Ca²⁺-dependent protein kinases (CDPK) stands out for its ability, depending on calcium levels, to activate key components of the defence system. However, calcium dependence prevents the effective use of CDPKs in comprehensive investigations of their functions. Previously, we showed that a modified constitutively active form of AtCPK1 improved heat tolerance in tobacco plants. At present, the role of calcium ions and their decoders in the regulation of heat tolerance is not fully understood. The response of plant cells to excessive temperature increases is regulated by complex interactions of hormonal signalling systems, among which the least studied is BR signalling. In the present work, we investigated the role of CDPK in the interactions of BR and ET signalling during heat stress. The use of a modified calcium-independent form of AtCPK1 in this work allowed us to answer a number of questions. We showed that dependence on heat-induced calcium ion currents determines the priority of the activation of ABA signalling. Thus, CPK-dependent activation of ABA signalling may not lead to an insufficient response from BR and ET signalling. Modified CPK1 activates BR signalling, which has a positive effect on the tolerance of transgenic plants to increased temperature. The obtained data shed light on heat-associated molecular processes and can draw attention to the possibility of using intradomain modifications of CDPK both for a comprehensive study of its functional features and as a bioengineering tool.