A laboratory simulation of Arabidopsis seed dormancy cycling provides new insight into its regulation by clock genes and the dormancy-related genes DOG1, MFT, CIPK23 and PHYA.

Angela J Hambidge,Steven Footitt,Hülya Ölçer‐Footitt,William E Finch‐Savage

doi:10.1111/pce.12940

Angela J Hambidge, Steven Footitt + Show 2 more

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https://doi.org/10.1111/pce.12940

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Abstract

Environmental signals drive seed dormancy cycling in the soil to synchronize germination with the optimal time of year, a process essential for species' fitness and survival. Previous correlation of transcription profiles in exhumed seeds with annual environmental signals revealed the coordination of dormancy‐regulating mechanisms with the soil environment. Here, we developed a rapid and robust laboratory dormancy cycling simulation. The utility of this simulation was tested in two ways: firstly, using mutants in known dormancy‐related genes [DELAY OF GERMINATION 1 (DOG1), MOTHER OF FLOWERING TIME (MFT), CBL‐INTERACTING PROTEIN KINASE 23 (CIPK23) and PHYTOCHROME A (PHYA)] and secondly, using further mutants, we test the hypothesis that components of the circadian clock are involved in coordination of the annual seed dormancy cycle. The rate of dormancy induction and relief differed in all lines tested. In the mutants, dog1‐2 and mft2, dormancy induction was reduced but not absent. DOG1 is not absolutely required for dormancy. In cipk23 and phyA dormancy, induction was accelerated. Involvement of the clock in dormancy cycling was clear when mutants in the morning and evening loops of the clock were compared. Dormancy induction was faster when the morning loop was compromised and delayed when the evening loop was compromised.

Highlights

Seeds are highly efficient sensors and interpreters of the prevailing environment and their environmental history
Dormancy cycling in Cape Verde Island (Cvi) under laboratory conditions: Cvi seeds in field soil are induced into deeper primary dormancy by low temperatures in winter, dormancy declines to low levels in response to higher temperatures in spring/summer; deeper dormancy is re-induced by autumn/winter low temperatures (Footitt et al 2011)
Primary dormant seeds on water did not germinate in the dark and germination was less than 5% at 20°C/light (Fig. 1(a))

Summary

Introduction

Seeds are highly efficient sensors and interpreters of the prevailing environment and their environmental history. When depth of dormancy is low seeds are sensitive to signals that inform of the spatial environment (e.g. light, nitrate and temperature). If these signals are not received to remove the final layer of dormancy seeds enter secondary dormancy (Finch-Savage and Footitt 2017). In this way seeds determine the time and place of plant establishment to synchronise their life cycle with favourable environments (Finch-Savage and Leubner-Metzger, 2006; Burghardt et al 2016; Springthorpe and Penfield 2015). Recent correlations of annual gene expression patterns in exhumed seeds with environmental signals in the field provided the first insight into the temporal integration of the molecular regulation of dormancy cycling (Footitt et al 2011, 2013, 2014)

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