Journal Article

Insight into Missing Genetic Links Between Two Evening-Expressed Pseudo-Response Regulator Genes <i>TOC1</i> and <i>PRR5</i> in the Circadian Clock-Controlled Circuitry in <i>Arabidopsis thaliana</i>

Shogo Ito, Yusuke Niwa, Norihito Nakamichi, Hideaki Kawamura, Takafumi Yamashino and Takeshi Mizuno

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 49, issue 2, pages 201-213
Published in print February 2008 | ISSN: 0032-0781
Published online February 2008 | e-ISSN: 1471-9053 | DOI:
Insight into Missing Genetic Links Between Two Evening-Expressed Pseudo-Response Regulator Genes TOC1 and PRR5 in the Circadian Clock-Controlled Circuitry in Arabidopsis thaliana

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry


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In Arabidopsis thaliana, many circadian clock-associated genes have been identified. Among them, the evening-expressed TOC1 (TIMING OF CAB EXPRESSION 1) gene plays a role by forming a transcriptional feedback core loop together with the morning-expressed CCA1 (CIRCADIAN CLOCK-ASSOCIATED 1) gene and its homologous LHY (LATE ELONGATED HYPOCOTYL) gene. TOC1 encodes a member of the PSEUDO-RESPONSE REGULATOR (PRR) family, including PRR9, PRR7, PRR5, PRR3,and PRR1/TOC1. The PRR genes other than TOC1 (or PRR1) also appear to be crucial for certain circadian-associated events. To clarify missing genetic linkages amongst these PRR genes, here we constructed a toc1 prr5 double knockdown mutant. In free-running circadian rhythms, the resulting toc1-2 prr5-11 mutant plants showed an extremely short period and reduced amplitude phenotype, which was more severe than that of the toc1-2 single mutant plant, suggesting a non-linear genetic interaction between TOC1 and PRR5. Surprisingly, the hallmark early flowering phenotype of toc1-2 in the short-day conditions had been converted to a markedly late flowering phenotype in the long-day conditions, when combined with the prr5-11 allele, which itself showed a subtle flowering phenotype. This unexpected genetic result (i.e. phenotypic sign conversion) suggested that the TOC1 and PRR5 genes are coordinately implicated in a non-linear and closed genetic circuitry. In the toc1-2 prr5-11 double mutant, the diurnal expression profile of CDF1 (CYCLING DOF FACTOR 1) was markedly de-repressed in the evening in the long-day conditions. These and other results of this study led us to propose the novel view that TOC1 might play bipartite roles in the control of flowering time within a closed circuitry; the one is a GI (GIGANTEA)-dependent negative role through CCA1/LHY, and the other is a CDF1-dependent positive role through cooperating closely with PRR5.

Keywords: Arabidopsis thaliana; Circadian rhythm; Clock component; Pseudo-response regulator; Photoperiodic flowering time

Journal Article.  7859 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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