Abstract
Dormancy cycling controls the seasonal conditions under which seeds germinate, and these conditions strongly influence growth and survival of plants. Several endogenous and environmental signals affect the dormancy status of seeds. Factors such as time, light, and temperature influence the balance between abscisic acid (ABA) and gibberellic acid (GA), two phytohormones that play a key role in seed dormancy and germination. High temperatures have been shown to increase ABA level and prevent seed germination, a process known as thermoinhibition. High temperature can also cause the acquisition of secondary dormancy, preventing germination of seeds upon their return to favorable germination conditions. The mechanisms and conditions linking thermoinhibition and secondary dormancy remain unclear. Phytochromes are photoreceptors known to promote seed germination of many plant species including Arabidopsis thaliana. Here, we demonstrate a role for PHYD in modulating secondary dormancy acquisition in seeds exposed to high temperature. We found that a functional PHYD gene is required for the germination of seeds that experienced high temperature, and that ABA- and GA-related gene expression during and after pre-incubation at high temperatures was altered in a phyD mutant. We further show that the level of PHYD mRNA increased in seeds pre-incubated at high temperature and that this increase correlates with efficient removal of the germination repressor PIL5.
Highlights
Phenology, the timing of a plant’s life events such as germination and flowering, has a major impact on survival and fitness (Chuine and Beaubien, 2001; Walther et al, 2002; Parmesan, 2006; Bradshaw and Holzapfel, 2008; Donohue et al, 2010)
We found that a functional PHYD gene is required for the germination of seeds that experienced high temperature, and that abscisic acid (ABA)- and gibberellic acid (GA)-related gene expression during and after pre-incubation at high temperatures was altered in a phyD mutant
Thermoinhibition is a process that occurs at high temperature to prevent germination of seeds under unfavorable temperatures
Summary
The timing of a plant’s life events such as germination and flowering, has a major impact on survival and fitness (Chuine and Beaubien, 2001; Walther et al, 2002; Parmesan, 2006; Bradshaw and Holzapfel, 2008; Donohue et al, 2010). Arabidopsis thaliana (Arabidopsis) seeds can survive under hot, dry conditions, whereas the vegetative state cannot; rosettes are resistant to cold temperatures, whereas the reproductive stage is susceptible to freezing damage. To accommodate these vulnerabilities, seeds of winter annuals are dispersed in the spring but only germinate in the autumn, allowing seedlings to avoid summer drought. Flowering occurs after winter in the following spring, allowing reproductive buds to avoid freezing temperatures. These delays allow each life stage to avoid the seasonal conditions that could cause its mortality. Germinating at the appropriate time of year is the first crucial developmental transition that determines survival, and it is under strong natural selection in numerous plant species including Arabidopsis (reviewed in Donohue et al, 2010)
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