LNK genes integrate light and clock signaling networks at the core of the Arabidopsis oscillator

Jul 3, 2013Proceedings of the National Academy of Sciences of the United States of America

LNK genes connect light and internal clock signals in the core timing system of Arabidopsis

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Abstract

A genomewide transcriptome analysis identified genes that link light signaling to the circadian clock in Arabidopsis thaliana.

A family of genes, LNK, is induced by night light and regulated by the circadian clock.
Most light-induced genes respond more strongly during the subjective day, aligning with typical plant physiological processes.
LNK1 and LNK2 genes are uniquely activated by light during the night when the clock is highly responsive.
These genes influence circadian rhythms, light-driven growth responses, and flowering timing by regulating specific clock and flowering genes in the afternoon.
LNK1 and LNK2 are repressed by core-clock genes in the afternoon and early night, indicating a complex regulatory interaction.

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Light signaling pathways and the circadian clock interact to help organisms synchronize physiological and developmental processes with periodic environmental cycles. The plant photoreceptors responsible for clock resetting have been characterized, but signaling components that link the photoreceptors to the clock remain to be identified. Here we describe a family of night light-inducible and clock-regulated genes (LNK) that play a key role linking light regulation of gene expression to the control of daily and seasonal rhythms in Arabidopsis thaliana. A genomewide transcriptome analysis revealed that most light-induced genes respond more strongly to light during the subjective day, which is consistent with the diurnal nature of most physiological processes in plants. However, a handful of genes, including the homologous genes LNK1 and LNK2, are more strongly induced by light in the middle of the night, when the clock is most responsive to this signal. Further analysis revealed that the morning phased LNK1 and LNK2 genes control circadian rhythms, photomorphogenic responses, and photoperiodic dependent flowering, most likely by regulating a subset of clock and flowering time genes in the afternoon. LNK1 and LNK2 themselves are directly repressed by members of the TIMING OF CAB1 EXPRESSION/PSEUDO RESPONSE REGULATOR family of core-clock genes in the afternoon and early night. Thus, LNK1 and LNK2 integrate early light signals with temporal information provided by core oscillator components to control the expression of afternoon genes, allowing plants to keep track of seasonal changes in day length.

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LNK genes integrate light and clock signaling networks at the core of the Arabidopsis oscillator

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