title: SPINDLY and GIGANTEA interact and act in Arabidopsis thaliana pathways involved in light responses, flowering, and rhythms in cotyledon movements.
abstract: SPINDLY (SPY) is a negative regulator of gibberellin signaling in Arabidopsis thaliana that also functions in previously undefined pathways. The N terminus of SPY contains a protein-protein interaction domain consisting of 10 tetratricopeptide repeats (TPRs). GIGANTEA (GI) was recovered from a yeast two-hybrid screen for proteins that interact with the TPR domain. GI and SPY also interacted in Escherichia coli and in vitro pull-down assays. 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. GI acts in the long-day flowering pathway upstream of CONSTANS (CO) and FLOWERING LOCUS T (FT). Loss of GI function causes late flowering and reduces CO and FT RNA levels. Consistent with SPY functioning in the long-day flowering pathway upstream of CO, spy-4 partially suppressed the reduced abundance of CO and FT RNA and the late flowering of gi-2 plants. Like gi, spy affects the free-running period of cotyledon movements. The free-running period was lengthened in spy-4 mutants and shortened in plants that overexpress SPY under the control of the 35S promoter of Cauliflower mosaic virus. When grown under red light, gi-2 plants have a long hypocotyl. This hypocotyl phenotype was suppressed in spy-4 gi-2 double mutants. Additionally, dark-grown and far-red-light-grown spy-4 seedlings were found to have short and long hypocotyls, respectively. The different hypocotyl length phenotypes of spy-4 seedlings grown under different light conditions are consistent with SPY acting in the GA pathway to inhibit hypocotyl elongation and also acting as a light-regulated promoter of elongation.
authors.affiliation: Department of Plant Biology and Plant Molecular Genetics Institute, University of Minesota, St. Paul, Minesota 55108, USA.
authors.forename: Tong-Seung
authors.initials: TS
authors.lastname: Tseng
authors.forename: Patrice A
authors.initials: PA
authors.lastname: Salomé
authors.forename: C Robertson
authors.initials: CR
authors.lastname: McClung
authors.forename: Neil E
authors.initials: NE
authors.lastname: Olszewski
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018548:Cotyledon / Q000254:growth & development / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000235:genetics; D035264:Flowers / Q000254:growth & development / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D018546:Hypocotyl / Q000254:growth & development / Q000378:metabolism; D008027:Light; D009068:Movement; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000528:radiation effects; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D004268:DNA-Binding Proteins; C418905:FT protein, Arabidopsis; C121183:GI protein, Arabidopsis; D012333:RNA, Messenger; D018749:RNA, Plant; D012097:Repressor Proteins; C101465:SPY protein, Arabidopsis; D014157:Transcription Factors