High impact information on ZTL

• Map-based cloning of ZTL identified a novel 609 amino acid polypeptide consisting of an amino-terminal PAS domain, an F box and six carboxy-terminal kelch repeats [1].
• Both yeast two-hybrid and in vitro binding studies show that there is a physical interaction between ADO1 and the photoreceptors CRY1 and phyB [2].
• We found that a loss-of-function ado1 mutant is altered in both gene expression and cotyledon movement in circadian rhythmicity [2].
• A third member of the ZTL gene family was identified in the Arabidopsis genome and was named LKP2 (for LOV kelch protein2) [3].
• This proteolysis is proteasome dependent, implicating ZTL itself as substrate for ubiquitination [4].

Biological context of ZTL

• This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype [5].
• Other mutants recovered include 11 new ztl alleles encompassing mutations in each of the ZTL protein domains [5].
• Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations [5].
• The LKP1 LOV is very similar to the LOV domains in NPH1, a plasma membrane-associated blue light receptor kinase that regulates phototropism (Huala, E., Oeller, P.W., Liscum, E., Han, I-S., Larsen, E. & Briggs, W.R. (1997) Science, 278, 2120-2123) [6].
• Transgenic plants with a beta-glucuronidase (GUS) reporter gene driven by a 1.5 kb LKP1 promoter display strong GUS activity in leaves [6].

Anatomical context of ZTL

• The action of phytochromes and cryptochromes in photoperiodism is augmented by ZEITLUPE (ZTL) and FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) acting as accessory photoreceptors on entrainment and interaction, respectively [7].
• The GFP-associated fluorescence in 35S:GFP-LKP1 plants is observed in nuclei and cytosol, indicating that LKP1 is a new nucleo-cytoplasmic factor that influences flowering time in the long day pathway of Arabidopsis [6].

Regulatory relationships of ZTL

• Our results show that the TOC1-ZTL interaction is important in the control of TOC1 protein stability, and is probably responsible for the regulation of circadian period by the clock [8].

Other interactions of ZTL

• LKP2 interacted not only with itself but also with other members of the family, LKP1 and FKF1 [9].
• Here we show that the effects of ZTL and ELF3 on circadian clock function and early photomorphogenesis are additive [10].
• ZTL overexpression does not delay flowering through changes in GIGANTEA or FLAVIN-BINDING, KELCH REPEAT, F-BOX levels, but through a ZTL-mediated reduction in CO expression [10].
• Targeted degradation of TOC1 by ZTL modulates circadian function in Arabidopsis thaliana [8].
• Interaction with PHYB was unaffected by mutation of any ZTL domain [5].

Analytical, diagnostic and therapeutic context of ZTL

• Here we use a newly characterized Arabidopsis suspension cell culture to establish that the rhythmic changes in the levels of the clock-associated F-box protein, ZTL, are posttranscriptionally controlled through different circadian phase-specific degradation rates [4].

References