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Ethylene-independent Promotion of Photomorphogenesis by Cytokinin Requires a Functional Cytokinin and Light Signaling Pathway.

ABSTRACT: The transition of skotomorphogenesis to photomorphogenesis is induced by the perception of light and is characterized by the inhibition of hypocotyl elongation and opening of cotyledons. Although it is known that the plant hormone cytokinin, when applied in high concentrations, inhibits hypocotyl elongation in the dark-grown Arabidopsis plants, it is unclear to what extent this response is the result of cytokinin alone or cytokinin-induced ethylene production. We show that treatment of etiolated seedlings in presence of ethylene inhibitors (eg. AgNO3) or treatment of the ethylene-resistant mutant ein2, resulted in a significant inhibition of hypocotyl elongation. This indicates that cytokinin induced de-etiolation is largely independent of ethylene and suggests a close connection between the cytokinin two component system and the light singalling networks. We show that this cytokinin signal is mainly mediated through the cytokinin receptor ARIBIDOPSIS HISTIDIN KINASE 3 (AHK3) and the ARABIDOPSIS RESPONSE REGULATORS 1 (ARR1) in combination with ARR12. Interestingly, mutation of COP1, DET1 and CIN4/COP10 renders plants insensitive to cytokinin and these factors are indispensable for the transcriptional response during cytokinin induced de-etiolation which indicates that a functional light signaling pathway is essential for this cytokinin response. In addition, the cytokinin effect on hypocotyl elongation is highly dependent on the ambient light conditions where higher light intensities causes a switch in the response to CK from an inhibitor to a promoter of hypocotyl elongation.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE108912 | GEO | 2018/10/01

REPOSITORIES: GEO

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Project description:Phytohormones play crucial roles in regulating many aspects of plant development. Although much has been learned about the effects of individual hormones, cross-talk between and integration of different hormonal signals are still not well understood. We present a study of MINI ZINC FINGER 1 (MIF1), a putative zinc finger protein from Arabidopsis, and suggest that it may be involved in integrating signals from multiple hormones. MIF1 homologs are highly conserved among seed plants, each characterized by a very short sequence containing a central putative zinc finger domain. Constitutive overexpression of MIF1 caused dramatic developmental defects, including dwarfism, reduced apical dominance, extreme longevity, dark-green leaves, altered flower morphology, poor fertility, reduced hypocotyl length, spoon-like cotyledons, reduced root growth, and ectopic root hairs on hypocotyls and cotyledons. In addition, 35S::MIF1 seedlings underwent constitutive photomorphogenesis in the dark, with root growth similar to that in the light. Furthermore, 35S::MIF1 seedlings were demonstrated to be non-responsive to gibberellin (GA) for cell elongation, hypersensitive to the GA synthesis inhibitor paclobutrazol (PAC) and abscisic acid (ABA), and hyposensitive to auxin, brassinosteroid and cytokinin, but normally responsive to ethylene. The de-etiolation defect could not be rescued by the hormones tested. Consistent with these observations, genome-scale expression profiling revealed that 35S::MIF1 seedlings exhibited decreased expression of genes involved in GA, auxin and brassinosteroid signaling as well as cell elongation/expansion, and increased expression of ABA-responsive genes. We propose that MIF1, or the protein(s) with which MIF1 interacts, is involved in mediating the control of plant development by multiple hormones. Experiment Overall Design: The experiment was designed to compared expression profiles of wild type (vector transformed Col) and 35S::MIF1 seedlings grown in the dark or white light. Twelve affymetrix ATH1 arrays were used for three biological replicates, six for comparison of light-grown seedlings and the other six for dark-grown seedlings. Wild-type seedlings were from three independent vector transformant lines(#1, #4 and #7). For the 35S::MIF1 transgenic seedlings, MIF1OE#124 was used for the first and second replicates, and MIF1OE#127 was used for the third replicate.

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Ethylene-independent Promotion of Photomorphogenesis by Cytokinin Requires a Functional Cytokinin and Light Signaling Pathway.

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