Disease relevance of GI

• GI and SPY also interacted in Escherichia coli and in vitro pull-down assays [1].
• Twenty-five plants were dipped into a suspension of Agrobacterium carrying a 2.5 kb antisense GI gene fragment from Arabidopsis, along with the gusA and bar reporter genes, all under the control of a CaMV 35S promoter [2].

High impact information on GI

• Control of circadian rhythms and photoperiodic flowering by the Arabidopsis GIGANTEA gene [3].
• Numerical simulations using the interlocking-loop model show that balancing LHY/CCA1 function against GI and other evening-expressed genes can largely account for temperature compensation in wild-type plants and the temperature-specific phenotypes of gi mutants [4].
• At 27 degrees C, a dynamic balance between GI and LHY allows temperature compensation in wild-type plants, but circadian function is impaired in lhy and gi mutant plants [4].
• These experiments demonstrated that GI acts between the circadian oscillator and CO to promote flowering by increasing CO and FT mRNA abundance [5].
• In contrast, ELF3 negatively regulates CO, FT, and GIGANTEA transcript levels, as the expression of all three genes is increased in elf3-1 [6].

Biological context of GI

• Therefore, GI plays a general role in controlling circadian rhythms, and this is different from its effect on the amplitude of expression of CO and FT [5].
• The phenotypes of spy and spy-4 gi-2 plants support the hypothesis that SPY functions with GI in pathways controlling flowering, circadian cotyledon movements, and hypocotyl elongation [1].
• The Arabidopsis GIGANTEA (GI) gene has been shown to regulate several developmental processes, including photoperiod-mediated flowering, phytochrome B signaling, circadian clock, and carbohydrate metabolism [7].
• This study provides evidence that down-regulation of the GI gene by co-suppression could delay bolting in a cold-sensitive long-day (LD) plant [2].
• Oxidative stress tolerance and longevity in Arabidopsis: the late-flowering mutant gigantea is tolerant to paraquat [8].

Associations of GI with chemical compounds

• GI gene was induced by cold stress, but not by salt, mannitol, and abscisic acid [7].
• We provide evidence that the GI response to blue and far-red light requires CRYPTOCHROME function in Arabidopsis [9].

Regulatory relationships of GI

• Also, we demonstrate that one of the mechanisms underlying GI protein oscillation occurs post-translationally via dark-induced proteolysis by the 26S proteasome [10].

Other interactions of GI

• As previously reported, the gi-2 mutation affects the period length and amplitude of CCA1 and LHY expression, and GI may act through a feedback loop to maintain a proper circadian function [11].
• Loss of GI function causes late flowering and reduces CO and FT RNA levels [1].
• 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 [6].
• The analysis of mutants of the photoperiod pathway showed epistasis of co and gi to the CRY2 alleles, indicating that cry2 needs the product of CO and GI genes to promote flowering [12].
• These cDNAs included a rice homolog of Arabidopsis GIGANTEA (GI), lir1, and a gene for myo-inositol 1-phosphate synthase, all of which were previously shown to be under the control of circadian clocks [13].

References