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Plant Physiol. 2019 Sep;181(1):305-318. doi: 10.1104/pp.19.00286. Epub 2019 Jun 10.

The Clock Gene TOC1 in Shoots, Not Roots, Determines Fitness of Nicotiana attenuata under Drought.

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Department of Molecular Ecology, Max Planck Institute for Chemical Ecology, 07745 Jena, Germany.
Centro de Investigación Científico Ecológico Académico, Lima 37, Peru.
Research Support Center in Molecular Diversity of Natural Products, Institute of Chemistry, University of São Paulo, São Paulo, SP 05508-000, Brazil.
Department of Molecular Ecology, Max Planck Institute for Chemical Ecology, 07745 Jena, Germany
German Centre for Integrative Biodiversity Research, 04103 Leipzig, Germany.
Department of Geography, University of Zurich, 8057 Zurich, Switzerland.


The highly conserved core circadian clock component TIMING OF CAB EXPRESSION1 (TOC1) contextualizes environmental stress responses in plants, for example by gating abscisic acid signaling and suppressing thermoresponsive growth. Selective interaction of TOC1 with PHYTOCHROME B under far-red-enriched light suggests a connection between circadian gating of light responses and sensitivity to ABA, an important regulator of growth and stress responses, including under drought. However, the fitness consequences of TOC1 function, particularly in the root, are poorly understood. Here, we used the desert annual, Nicotiana attenuata, to investigate the function of TOC1 in shoots and roots for maintaining fitness under drought, in both field and glasshouse experiments. Despite marked decreases in leaf water loss, TOC1-deficient lines failed to maintain fitness in response to drought stress as measured by total seed capsule production. Restoring TOC1 transcript levels in shoots via micrografting was sufficient to restore wild-type drought responses under field conditions. Microarrays identified a coexpression module in leaves strongly linking red and far-red light signaling to drought responses in a TOC1-dependent manner, but experiments with phytochrome-deficient lines revealed that the effects of TOC1 deficiency under drought cannot be attributed to changes in red/far-red light perception alone. Taken together, these results elucidate the sophisticated, tissue-dependent role of the circadian clock in maintaining fitness in the face of long-term abiotic stresses such as drought.

[Available on 2020-09-01]

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