Structural Aspects of Multistep Phosphorelay-Mediated Signaling in Plants

Abstract

The multistep phosphorelay (MSP) is a central signaling pathway in plants integrating a wide spectrum of hormonal and environmental inputs and controlling numerous developmental adaptations. For the thorough comprehension of the molecular mechanisms underlying the MSP-mediated signal recognition and transduction, the detailed structural characterization of individual members of the pathway is critical. In this review we describe and discuss the recently known crystal and nuclear magnetic resonance structures of proteins acting in MSP signaling in higher plants, focusing particularly on cytokinin and ethylene signaling in Arabidopsis thaliana. We discuss the range of functional aspects of available structural information including determination of ligand specificity, activation of the receptor via its autophosphorylation, and downstream signal transduction through the phosphorelay. We compare the plant structures with their bacterial counterparts and show that although the overall similarity is high, the differences in structural details are frequent and functionally important. Finally, we discuss emerging knowledge on molecular recognition mechanisms in the MSP, and mention the latest findings regarding structural determinants of signaling specificity in the Arabidopsis MSP that could serve as a general model of this pathway in all higher plants.

Functional Divergence of Poplar Histidine-Aspartate Kinase HK1 Paralogs in Response to Osmotic Stress

“…Our results are in agreement with those obtained with CKI1 showing interaction specificity with only three AHP among six in Arabidopsis [46]. Overall, these findings strengthen the hypothesis that HPt proteins participate to a certain level of interaction specificity within the MSP system [47,48], validating HPt2 and HPt9 as partners probably involved in poplar MSP linked to drought.…”

Cytokinin perception in potato: New features of canonic players

“…Conserved amino acids and consensus motifs (N, G1, F, G2) are indicated. According to conventional terminology, the catalytic module consists of dimerization and histidine phosphotransfer domain (DHpD), and catalytic and ATP-binding domain (CAD) (Mayerhofer et al ., 2015; Pekárová et al ., 2016). Scales at the bottom of the structures indicate the length in aa number.…”

New Insight into HPts as Hubs in Poplar Cytokinin and Osmosensing Multistep Phosphorelays: Cytokinin Pathway Uses Specific HPts

“…The notion of HPts as hub proteins is a concept that emerged a few years ago with the growing amount of MSP interaction network identification [21,54,55]. As integrative proteins in MSP are able to interact with upstream and downstream partners, it was proposed that HPt proteins act as hubs within the CK signaling pathway in Arabidopsis [21].…”

“…As integrative proteins in MSP are able to interact with upstream and downstream partners, it was proposed that HPt proteins act as hubs within the CK signaling pathway in Arabidopsis [21]. This idea was slightly modulated by Pekárová et al [54] who argued that HPts are not unspecific signaling hubs but can achieve a certain level of interaction specificity. In Arabidopsis, numerous examples have unveiled the crosstalk between CK signaling and other pathways.…”