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.

Type II protein arginine methyltransferase 5 (PRMT5) is required for circadian period determination in Arabidopsis thaliana

“…However, phosphorylation also can alter protein-protein and protein-DNA interactions as well as protein activity without concomitant effects on protein stability. Posttranslational decoration with N-acetylglucosamine also plays a significant role in Arabidopsis clock function, because mutational loss of or overexpression of the O-linked β-N-acetylglucosamine transferase, Spindly (SPY), lengthens or shortens, respectively, the circadian period (45). The period lengthening associated with mutational disruption of prmt5 indicates that Rsme2 represents a decoration important for the functioning of the plant clock and possibly for clocks in general.…”

Plant Circadian Rhythms

“…Recently, a second type of posttranslational modification has been implicated in clock function. SPINDLY is an N-acetylglucosamine transferase that decorates GI, among other targets, and spy mutants exhibit altered rhythms in leaf movement (Tseng et al, 2004).…”

The Arabidopsis rcn1-1 Mutation Impairs Dephosphorylation of Phot2, Resulting in Enhanced Blue Light Responses

“…Arabidopsis phot2 cDNA (either full length or truncated for the domain analysis) was amplified with forward primer 59-GCTCTAGAGC-CATGGAGAGGCCAAGAGCCC-39 and reverse primer 59-AACTGCAGT-TAGAAGAGGTCAATGTCCAAG-39 and subcloned to the NcoI and PstI sites of the pAS1-CYH2 plasmid. Yeast transformation and library screening were as described (Tseng et al, 2004). The b-galactosidase activity assays were conducted using o-nitrophenyl-b-D-galactopyranoside (USB) as a substrate.…”