Environmental perception avenues: the interaction of cytokinin and environmental response pathways

Abstract

Cytokinins were discovered in the 1950s by their ability to promote cell division in cultured plant cells. Recently, there have been significant breakthroughs in our understanding of the biosynthesis, metabolism, perception and signal transduction of this phytohormone. These advances, coupled with physiological and other approaches, have enabled remarkable progress to be made in our understanding of the interactions between cytokinin function and environmental inputs. In this review, we first highlight the most recent advances in our understanding of cytokinin biosynthesis, metabolism and signalling. We then discuss how various environmental signals interact with these pathways to modulate plant growth, development and physiology.

Alterations of Endogenous Hormonal Levels in Plants under Drought and Salinity

“…Moreover, the authors proposed that CKs levels reduction enhance survival rates of the CK-deficient plants by minimizing water loss. Similarly, under salinity some reports have demonstrated that the endogenous levels and transport of CKs were also reduced in several plant species [77]. Studies with the halophytes Suaea depressa and S. maritima suggested that CKs applications may emphasize the symptoms associated with salt stress [78].…”

The Cytokinin Receptors of Arabidopsis Are Located Mainly to the Endoplasmic Reticulum

“…They also function in mediating the plant response to environmental signals, such as biotic and abiotic stresses (Argueso et al, 2009;Werner and Schmü lling, 2009). The cytokinin signal is perceived by membrane-bound sensor His kinases and further transduced by a multistep variant of the two-component signaling system (Heyl and Schmü lling, 2003;Kakimoto, 2003;Bishopp et al, 2006).…”

Attenuation of cytokinin signaling via proteolysis of a Type-B response regulator

“…8 The output intensities of TCS signaling are primarily regulated by post-transcriptional and post-translational modifications of TCS components. 3 For example, in Arabidopsis, the expression levels of AHKs (histidine kinase proteins), AHPs (histidine phosphotransfer proteins) and ARRs fluctuate in response to changing environmental conditions. 3 At the protein level, sequential phosphorylations initiated by cytokinin receptors are essential for propagating cytokinin signals.…”

“…3 For example, in Arabidopsis, the expression levels of AHKs (histidine kinase proteins), AHPs (histidine phosphotransfer proteins) and ARRs fluctuate in response to changing environmental conditions. 3 At the protein level, sequential phosphorylations initiated by cytokinin receptors are essential for propagating cytokinin signals. However, the duration and intensity of these phosphorylation-propagated signals must be properly mediated by negative regulatory mechanisms.…”

“…3 At the cellular level, cytokinins are recognized by CHASE-domain-containing histidine kinases located in the plasma membrane 4 and/or the endoplasmic reticulum (ER). [5][6][7] Upon cytokinin binding, type-B response regulators in the nucleus are activated via His-Asp multi-step phospho-relays similar to those observed in bacterial twocomponent systems (TCS).…”