Compensatory Mutations in GI and ZTL May Modulate Temperature Compensation in the Circadian Clock

Abstract

Circadian systems share the three properties of entrainment, free-running period, and temperature compensation (TC). TC ensures nearly the same period over a broad range of physiologically relevant temperatures; however, the mechanisms behind TC remain poorly understood. Here, we identify single point mutations in two key elements of the Arabidopsis circadian clock, GIGANTEA (GI) and ZEITLUPE (ZTL), which likely act as compensatory substitutions to establish a remarkably constant free-running period over a wide range of temperatures. Using near-isogenic lines generated from the introgression of the Cape Verde Islands (Cvi) alleles of GI and ZTL into the Landsberg erecta (Ler) background, we show how longer periods in the Cvi background at higher temperatures correlate with a difference in strength of the GI/ZTL interaction. Pairwise interaction testing of all GI/ZTL allelic combinations shows similar affinities for isogenic alleles at 22°C, but very poor interaction between GI (Cvi) and ZTL (Cvi) at higher temperature. In vivo, this would result in lower ZTL levels at high temperatures leading to longer periods in the Cvi background. Mismatched allelic combinations result in extremely strong or weak GI/ZTL interactions, indicating how the corresponding natural variants likely became fixed through epistatic selection. Additionally, molecular characterization of GI (Cvi) reveals a novel functional motif that can modulate the GI/ZTL interaction as well as nucleocytoplasmic partitioning. Taken together, these results identify a plausible temperature-dependent molecular mechanism, which contributes to the robustness of TC through natural variation in GI and ZTL alleles found on the Cape Verde Islands.

SDC mediates DNA methylation-controlled clock pace by interacting with ZTL in Arabidopsis

“…As the circadian period varies among different Arabidopsis ecotypes due to their natural geographic origin ( 54 ), we further examined the effect of 5-Aza-dC treatment on the circadian clock in a few additional natural accessions, including Cvi ( Cape verde islands ), Ws ( Wassileskija ) and L er ( Landsberg erecta ) ( Supplementary Figure S1D–F ). Consistent with previous findings ( 55 , 56 ), the Cvi ecotype showed a relatively shorter circadian period (21.93 ± 0.16 h) without treatment compared to L er (23.65 ± 0.08 h) and Ws (23.83 ± 0.05 h) (Figure 1I ). Nevertheless, all examined ecotypes displayed a significantly lengthened circadian period with a range of 0.68–1.37 h after 20 mg/l 5-Aza-dC treatment compared to their respective mock-treated controls (Figure 1I and Supplementary Table S3 ) (Cvi 23.30 ± 0.22 h; L er 24.68 ± 0.07 h, and Ws 24.51 ± 0.04 h).…”

Post-Translational Mechanisms of Plant Circadian Regulation

“…These results suggest that a mutual stabilization of ZTL and GI occurs in the cytoplasm, and GI stabilization and cytoplasmic retention occurs naturally through a LOV domain mediated GI-ZTL interaction, with ZTL indirectly regulating GI nuclear pools by sequestering GI to the cytosol. This notion is supported by a recent study in which the reduced strength of GI-ZTL interactions in the Arabidopsis Cape Verde Islands ecotype, correlate with the low ZTL abundance [144]. The GI L 712 XXLXXL 718 motif mediates GI-ZTL interaction and also determines GI nucleocytoplasmic partitioning.…”

Evolutionary Analysis and Functional Identification of Clock-Associated PSEUDO-RESPONSE REGULATOR (PRRs) Genes in the Flowering Regulation of Roses

“…The circadian clock of plants is referred to an endogenous oscillator regulating various plant physiological processes such as photomorphogenesis, stress responses, and flowering [28][29][30][31][32][33][34][35][36][37][38]. PRR genes are very important in plant flowering in response to circadian rhythm [13].…”