Cytokinin and auxin relationship goals

Auxin-cytokinin and auxin-gibberellin interactions during morphogenesis of the The goals of this study were to determine if auxin application can rescue any of the Cytokinins/pharmacology; Dose-Response Relationship, Drug; Genotype. Endogenous auxins and cytokinins were quantitated in 24 axenic microalgal strains from the Chlorophyceae, Trebouxiophyceae, Ulvophyceae. We begin with an overview of cytokinin and auxin metabolism and signaling . The AHPs are the downstream targets of the AHK cytokinin receptors However, there are also antagonistic relationships revealed during the.

The interaction between auxin and cytokinin is particularly important to control a few developmental processes, such as the formation and maintenance of meristems that are essential to establish the whole plant body.

For example, the shoot meristems give rise to the above-ground parts of a plant, whereas the root meristems produce the below-ground parts.

Control of cytokinin and auxin homeostasis in cyanobacteria and algae

Many recent studies have provided important information for the understanding of the molecular mechanisms of auxin—cytokinin interaction in the regulation of meristem development. Maintenance of the cellular optimum auxin concentration can be controlled at multiple levels, such as biosynthesis, transport, perception, and signaling.

These multiple regulation pathways contribute to the differential auxin distribution within tissues at different developmental stages.

Secret Relationships [Behind Relationship Goals

Auxin polar transport is required to direct auxin flows and to form auxin gradients in plants, which are critical for developmental pattern formation. In Arabidopsis, three protein families are required to mediate auxin transport between cells: Besides the biosynthesis and transport of auxin, auxin signaling through receptors and downstream signaling components has also been suggested to be the regulating mechanism for many developmental processes.

This E3 complex is involved in proteasome-mediated protein degradation Ruegger et al.

Auxin–Cytokinin Interaction Regulates Meristem Development

Thus far, two classes of transcriptional regulators represent the core of auxin signaling: The ARFs could function as either activators or repressors in the regulation of auxin-induced gene expression Ulmasov et al. Like auxin, cytokinin is also a key regulator for various aspects of plant growth and development.

Cytokinin homeostasis is spatially and temporally regulated by a fine balance between synthesis and catabolism. The first enzyme identified in the Arabidopsis cytokinin biosynthetic pathway is adenosine phosphate-isopentenyltransferases IPTs. Another landmark is the identification of two cytochrome P monooxygenases, CYPA1 and CYPA2, which catalyze the hydroxylation at the prenyl side chain of the iP-nucleotides to synthesize tZ-nucleotides Takei et al.

In contrast to auxin, cytokinin is perceived in plants through a multi-step phosphorelay pathway similar to the bacterial two-component signaling system Kakimoto, ; To and Kieber, Among them, cytokinins CKs represent one of the most important groups, playing a key role in cytokinesis and regulation of the cell cycle.

In addition, CKs affect a number of other physiological processes, such as morphogenesis, apical dominance, leaf senescence, chloroplast development and seed dormancy Miller et al.

Control of cytokinin and auxin homeostasis in cyanobacteria and algae

According to their structure and physiological activity, CKs are categorized into 1 bioactive forms, including free bases and corresponding nucleosides and their precursors nucleotidesand 2 non-active or weakly active forms, CK-O- and CK-N-glucosides Sakakibara, In contrast to vascular plants, none or only trace amounts of CK N-glucosylated forms and mostly rather low levels of CK O-glucosides have been reported in cyanobacteria or algae Stirk et al. Cyanobacteria as photosynthetic microorganisms exhibit beneficial effects on plant growth through their CK-like activity in processes of atmospheric nitrogen fixation, and thus are successfully utilized in agriculture Stirk et al.

A relatively simple CK metabolism in cyanobacteria was predicted based on a search of CK-related homologous genes involved in CK biosynthesis and degradation pathways. Recently, the function of gene encoded adenylate-IPT in the cyanobacterium Nostoc sp.

In addition, no matching CKX sequences were detected in Synechocystis sp. On the other hand, the regulatory effect of CKs on cyanobacteria metabolism has been reported for Synechocystis sp. Strongly activated RNA transcription in the presence of transZ and CK-binding protein suggested the existence of a potential system of CK signal recognition, which might be transferred to the plant cell in cyanobacteria Selivankina et al. PCC was found, there are still no details concerning gene expression and function Anantharaman and Aravind, ; Selivankina et al.

Algae are a highly diverse, non-monophyletic group of photosynthetic eukaryotes occurring in marine, freshwater and land habitats, where sufficient photosynthetic light is available Lewis and McCourt, It was hypothesized that cytokinin may affect enzymes that regulate protein synthesis and degradation. This pathway is initiated by cytokinin binding to a histidine kinase receptor in the endoplasmic reticulum membrane.

This results in the autophosphorylation of the receptor, with the phosphate then being transferred to a phosphotransfer protein.

Auxin–Cytokinin Interaction Regulates Meristem Development

The phosphotransfer proteins can then phosphorylate the type-B response regulators RR which are a family of transcriptions factors. The phosphorylated, and thus activated, type-B RRs regulate the transcription of numerous genes, including the type-A RRs.

The type-A RRs negatively regulate the pathway. For example, cytokinins have been described to induce resistance against Pseudomonas syringae in Arabidopsis thaliana [14] and Nicotiana tabacum.