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3D Domain Swapping Dimerization of the Receiver Domain of Cytokinin Receptor CRE1 From Arabidopsis thaliana and Medicago truncatula.

ABSTRACT: Cytokinins are phytohormones regulating many biological processes that are vital to plants. CYTOKININ RESPONSE1 (CRE1), the main cytokinin receptor, has a modular architecture composed of a cytokinin-binding CHASE (Cyclases/Histidine kinases Associated Sensory Extracellular) domain, followed by a transmembrane fragment, an intracellular histidine kinase (HK) domain, and a receiver domain (REC). Perception of cytokinin signaling involves (i) a hormone molecule binding to the CHASE domain, (ii) CRE1 autophosphorylation at a conserved His residue in the HK domain, followed by a phosphorelay to (iii) a conserved Asp residue in the REC domain, (iv) a histidine-containing phosphotransfer protein (HPt), and (v) a response regulator (RR). This work focuses on the crystal structures of the REC domain of CRE1 from the model plant Arabidopsis thaliana and from the model legume Medicago truncatula. Both REC domains form tight 3D-domain-swapped dimers. Dimerization of the REC domain agrees with the quaternary assembly of the entire CRE1 but is incompatible with a model of its complex with HPt, suggesting that a considerable conformational change should occur to enable the signal transduction. Indeed, phosphorylation of the REC domain can change the HPt-binding properties of CRE1, as shown by functional studies.

SUBMITTER: Tran LH

PROVIDER: S-EPMC8498639 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Legumes can establish on nitrogen-deprived soils a symbiotic interaction with Rhizobia bacteria, leading to the formation of nitrogen-fixing root nodules. Cytokinin phytohormones are critical for triggering root cortical cell divisions at the onset of nodule initiation. Cytokinin signaling is based on a Two-Component System (TCS) phosphorelay cascade, involving successively Cytokinin-binding Histidine Kinase receptors, phosphorelay proteins shuttling between the cytoplasm and the nucleus, and Type-B Response Regulator (RRB) transcription factors activating the expression of cytokinin primary response genes. Among those, Type-A Response Regulators (RRA) exert a negative feedback on the TCS signaling. To determine whether the legume plant nodulation capacity is linked to specific features of TCS proteins, a genome-wide identification was performed in six legume genomes (Cajanus cajan, pigeonpea; Cicer arietinum, chickpea; Glycine max, soybean; Phaseolus vulgaris, common bean; Lotus japonicus; Medicago truncatula). The diversity of legume TCS proteins was compared to the one found in two non-nodulating species, Arabidopsis thaliana and Vitis vinifera, which are references for functional analyses of TCS components and phylogenetic analyses, respectively. RESULTS:A striking expansion of non-canonical RRBs was identified, notably leading to the emergence of proteins where the conserved phosphor-accepting aspartate residue is replaced by a glutamate or an asparagine. M. truncatula genome-wide expression datasets additionally revealed that only a limited subset of cytokinin-related TCS genes is highly expressed in different organs, namely MtCHK1/MtCRE1, MtHPT1, and MtRRB3, suggesting that this "core" module potentially acts in most plant organs including nodules. CONCLUSIONS:Further functional analyses are required to determine the relevance of these numerous non-canonical TCS RRBs in symbiotic nodulation, as well as of canonical MtHPT1 and MtRRB3 core signaling elements.

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3D Domain Swapping Dimerization of the Receiver Domain of Cytokinin Receptor CRE1 From Arabidopsis thaliana and Medicago truncatula.

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