Plant and Cell Physiology Advance Access published online on January 4, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcm178
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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
1 Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
2 Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
3 Corresponding author: Shogo Ito, Fax: +81-52-789-4091, E-mail: i052001d{at}mbox.nagoya-u.ac.jp
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Abstract |
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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) genes. 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 severer 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 at 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.
4These two authors contributed equally to this study.
(Received November 23, 2007; Accepted December 19, 2007)
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