Cytokinin Perception in Ancient Plants beyond Angiospermae

Abstract

Cytokinins (CKs) control many plant developmental processes and responses to environmental cues. Although the CK signaling is well understood, we are only beginning to decipher its evolution. Here, we investigated the CK perception apparatus in early-divergent plant species such as bryophyte Physcomitrium patens, lycophyte Selaginella moellendorffii, and gymnosperm Picea abies. Of the eight CHASE-domain containing histidine kinases (CHKs) examined, two CHKs, PpCHK3 and PpCHK4, did not bind CKs. All other CHK receptors showed high-affinity CK binding (KD of nM range), with a strong preference for isopentenyladenine over other CK nucleobases in the moss and for trans-zeatin over cis-zeatin in the gymnosperm. The pH dependences of CK binding for these six CHKs showed a wide range, which may indicate different subcellular localization of these receptors at either the plasma- or endoplasmic reticulum membrane. Thus, the properties of the whole CK perception apparatuses in early-divergent lineages were demonstrated. Data show that during land plant evolution there was a diversification of the ligand specificity of various CHKs, in particular, the rise in preference for trans-zeatin over cis-zeatin, which indicates a steadily increasing specialization of receptors to various CKs. Finally, this distinct preference of individual receptors to different CK versions culminated in vascular plants, especially angiosperms.

Abscisic Acid and Cytokinins Are Not Involved in the Regulation of Stomatal Conductance of Scots Pine Saplings during Post-Drought Recovery

“…Among three free active CKs found in pine needles, t Z and iP were shown to bind with high affinity to Picea abies CHK receptors, whereas PaCHK affinity for DZ was one to two orders of magnitude lower [ 35 ]. Therefore, the dynamics of t Z and iP are likely to have more biological significance than DZ.…”

“…Moreover, during Experiment 2, spraying with different concentrations of 6-BAP influenced neither recovery of needle water status (Ψ leaf , RWC) nor recovery of stomatal conductance, and these parameters recovered by the end of the 3-week recovery period independently of CK spraying. It is important to note that 6-BAP is bound by CHK receptors of Picea abies plants with an affinity intermediate between those of t Z/iP and DZ [ 35 ], and it is reasonable to expect that 6-BAP can also bind to CHK receptors in pine needles. It can be concluded that partial suppression of stomatal opening in pine plants is unresponsive to decreased ABA accumulation, increased CK content and CK/ABA ratio and exogenous CK treatment, which implies that this suppression is not mediated by sustained effects of water stress on plant hormonal balance.…”

Perception, Transduction and Crosstalk of Auxin and Cytokinin Signals

“… Venn diagram summarizing the IJMS Special Issue “Perception, Transduction and Crosstalk of Auxin and Cytokinin Signals” [ 2 , 5 , 8 , 10 , 13 , 15 , 16 , 17 , 19 , 21 ]. Areas associated with cytokinin and auxin are marked in green and pink, respectively; the overlapping region corresponds to both hormones.…”

“…Hormone perception is based on sensing receptor proteins, so receptors are key components of signaling cascades. Lomin et al (2021) [ 5 ], from the Timiryazev Institute of Plant Physiology (Moscow, Russia), with the participation of Dr. Heyl (Adelphi University, Garden City, USA), set out to investigate the cytokinin perception apparatus in early divergent plant species such as the bryophyte Physcomitrium patens , lycophyte Selaginella moellendorffii , and gymnosperm Picea abies . All the receptors or their individual sensory modules were analyzed in terms of their cytokinin-binding affinities, their ligand specificity, and the pH-dependencies of hormone binding.…”

In Planta, In Vitro and In Silico Studies of Chiral N6-Benzyladenine Derivatives: Discovery of Receptor-Specific S-Enantiomers with Cytokinin or Anticytokinin Activities

“…The cytokinin signaling system is one of the most important regulatory systems in all land plants, including evolutionarily ancient species [ 1 , 2 , 3 , 4 , 5 , 6 ]. It functions at every stage of plant ontogenesis, primarily regulating cell proliferation and differentiation [ 7 , 8 , 9 , 10 ].…”