Setting-up a fast and reliable cytokinin biosensor based on a plant histidine kinase receptor expressed in Saccharomyces cerevisiae

Plant hormone profile and control over isoprene biosynthesis in a tropical tree Ficus septica

Plant hormone signalling and the circadian clock have been implicated in the transcriptional control of isoprene biosynthesis. To gain more insight into the hormonal control of isoprene biosynthesis, the present study measured plant hormone concentrations in jasmonic acid (JA)-treated leaves of our previous model study, examined their relationship with gene expression of isoprene synthase (IspS) and hormone signalling transcription factors. Of the plant hormones, IAA and JA-Ile and their related transcription factors (MYC2 and SAUR21) were significantly correlated with IspS gene expression. Concentrations of cytokinins, isopentenyladenine (iP), trans-zeatin riboside (tZR) and cis-zeatin riboside (cZR), were similarly significantly correlated with IspS expression. However, there was no significant correlation between their related transcription factor (ARR-B) and IspS expression. The circadian clock-related gene PRR7, but not the transcription factor LHY, was highly correlated with IspS expression. These results suggest that the hormonal balance between JA-Ile and IAA plays a central role in transcriptional regulation of IspS through the transcription factors MYC2 and SAUR21, the early auxin responsive genes. The putative cis-acting elements for SAUR on the IspS promoter (TGTCNN and CATATG), in addition to the G-box for MYC2, support the above proposal. These results provide insightful information on the core components of plant hormone-related regulation of IspS under coordination with the circadian clock genes.

Beyond transport: cytokinin ribosides are translocated and active in regulating the development and environmental responses of plants

Riboside type cytokinins are key components in cytokinin metabolism, transport, and sensitivity, making them important functional signals in plant growth and development and environmental stress responses. Cytokinin (CKs) are phytohormones that regulate multiple processes in plants and are critical for agronomy, as they are involved in seed filling and plant responses to biotic and abiotic stress. Among the over 30 identified CKs, there is uncertainty about the roles of many of the individual CK structural forms. Cytokinin free bases (CKFBs), have been studied in great detail, but, by comparison, roles of riboside-type CKs (CKRs) in CK metabolism and associated signaling pathways and their distal impacts on plant physiology remain largely unknown. Here, recent findings on CKR abundance, transport and localization, are summarized, and their importance in planta is discussed. The history of CKR analyses is reviewed, in the context of the determination of CK metabolic pathways, and research on CKR affinity for CK receptors, all of which yield essential insights into their functions. Recent studies suggest that CKR forms are a lot more than a group of transport CKs and, beyond this, they play important roles in plant development and responses to environmental stress. In this context, this review discusses the involvement of CKRs in plant development, and highlight the less anticipated functions of CKRs in abiotic stress tolerance. Based on this, possible mechanisms for CKR modes of action are proposed and experimental approaches to further uncover their roles and future biotechnological applications are suggested.

Electrochemical biosensor for cytokinins based on the CHASE domain of Arabidopsis histidine kinases 4

In this study, An AHK4 CHASE domain was used to construct an electrochemical cytokinin biosensor using ferrocene as the electrochemical mediator. Upon addition of cytokinin, the binding of cytokinin and AHK4 led to dimerization, which blocked electron transfer between ferrocene and the electrode, and the redox peak current of ferrocene was gradually reduced. Cytokinin was detected by recording the change of the ferrocene redox peak current. The biosensor shows a linear range of 50-400 nM with a linear regression equation of i_p = 0.0086c + 0.732 (R² = 0.993) with i_p in μA and c in nM and a detection limit (LOD) of 1.5 nM (S/N = 3). The biosensor exhibits excellent performance that avoids interference of other types of plant hormones and was successfully applied to the detection of cytokinins in bean sprouts.

Cytokinin and Ethylene Cell Signaling Pathways from Prokaryotes to Eukaryotes

Cytokinins (CKs) and ethylene (ET) are among the most ancient organic chemicals on Earth. A wide range of organisms including plants, algae, fungi, amoebae, and bacteria use these substances as signaling molecules to regulate cellular processes. Because of their ancestral origin and ubiquitous occurrence, CKs and ET are also considered to be ideal molecules for inter-kingdom communication. Their signal transduction pathways were first historically deciphered in plants and are related to the two-component systems, using histidine kinases as primary sensors. Paradoxically, although CKs and ET serve as signaling molecules in different kingdoms, it has been supposed for a long time that the canonical CK and ET signaling pathways are restricted to terrestrial plants. These considerations have now been called into question following the identification over recent years of genes encoding CK and ET receptor homologs in many other lineages within the tree of life. These advances shed new light on the dissemination and evolution of these hormones as both intra- and inter-specific communication molecules in prokaryotic and eukaryotic organisms.

The Origins and Roles of Methylthiolated Cytokinins: Evidence From Among Life Kingdoms

Cytokinins (CKs) are a group of adenine-derived, small signaling molecules of crucial importance for growth and multiple developmental processes in plants. Biological roles of classical CKs: isopentenyladenine (iP), trans and cis isomers of zeatin (tZ, cZ), and dihydrozeatin, have been studied extensively and their functions are well defined in many aspects of plant physiology. In parallel, extensive knowledge exists for genes involved in tRNA modifications that lead to the production of tRNA-bound methylthiolated CKs, especially in bacterial and mammalian systems. However, not much is known about the origins, fates, and possible functions of the unbound methylthiolated CKs (2MeS-CKs) in biological systems. 2MeS-CKs are the free base or riboside derivatives of iP or Z-type CKs, modified by the addition of a thiol group (–SH) at position 2 of the adenine ring that is subsequently methylated. Based on the evidence to date, these distinctive CK conjugates are derived exclusively via the tRNA degradation pathway. This review summarizes the knowledge on the probable steps involved in the biosynthesis of unbound 2MeS-CKs across diverse kingdoms of life. Furthermore, it provides examples of CK profiles of organisms from which the presence of 2MeS-CKs have been detected and confirms a close association and balance between the production of classical CKs and 2MeS-CKs. Finally, it discusses available reports regarding the possible physiological functions of 2MeS-CKs in different biological systems.

Natural and synthetic cytokinins and their applications in biotechnology, agrochemistry and medicine

The review is devoted to cytokinins — classical plant hormones known for more than six decades. Nevertheless, different aspects of the action of cytokinins are still being investigated. Relevant studies produced interesting, often unexpected, results, which cast doubt on the old paradigms and open new prospects for the use of these phytohormones. Particular attention is given to recent advances in the applications of natural cytokinins and their synthetic analogues in biotechnology, agriculture, medicine and cosmetics. The chemical synthesis, properties and the possible use of artificial cytokinins are considered in detail. The review is aimed at researchers interested in the development and applications of new biologically active compounds with a wide spectrum of action on diverse biological objects, from plants to humans.

The bibliography includes 233 references.

What do archaeal and eukaryotic histidine kinases sense?

Signal transduction systems configured around a core phosphotransfer step between a histidine kinase and a cognate response regulator protein occur in organisms from all domains of life. These systems, termed two-component systems, constitute the majority of multi-component signaling pathways in Bacteria but are less prevalent in Archaea and Eukarya. The core signaling domains are modular, allowing versatility in configuration of components into single-step phosphotransfer and multi-step phosphorelay pathways, the former being predominant in bacteria and the latter in eukaryotes. Two-component systems regulate key cellular regulatory processes that provide adaptive responses to environmental stimuli and are of interest for the development of antimicrobial therapeutics, biotechnology applications, and biosensor engineering. In bacteria, two-component systems have been found to mediate responses to an extremely broad array of extracellular and intracellular chemical and physical stimuli, whereas in archaea and eukaryotes, the use of two-component systems is more limited. This review summarizes recent advances in exploring the repertoire of sensor histidine kinases in the Archaea and Eukarya domains of life.