A new role for phytochromes in temperature‐dependent germination

Abstract

Summary• Germination timing is a fundamental life-history trait, as seedling establishment predicates realized fitness in the wild. Light and temperature are two important cues by which seeds sense the proper season of germination. Using Arabidopsis thaliana , we provide evidence that phytochrome-mediated germination pathways simultaneously respond to light and temperature cues in ways that affect germination.• Phytochrome mutant seeds were sown on agar plates and allowed to germinate in lit, growth chambers across a range of temperatures (7 ° C to 28 ° C).• phyA had an important role in promoting germination at warmer temperatures, phyE was important to germination at colder temperatures and phyB was important to germination across a range of temperatures.• Different phytochromes were required for germination at different temperatures, indicating a restriction or even a potential specialization of individual phytochrome activity as a function of temperature. This temperature-dependent activity of particular phytochromes reveals a potentially novel role for phytochrome pathways in regulating the seasonal timing of germination.

Induction of Dormancy in Arabidopsis Summer Annuals Requires Parallel Regulation of DOG1 and Hormone Metabolism by Low Temperature and CBF Transcription Factors

“…However, we consider this unlikely because CBF transcription is not temperature responsive at normal red/far-red ratios in the temperature range used for this study (Franklin and Whitelam, 2007). It would be interesting to test whether CBFs have a role in the regulation of dormancy by light quality (as opposed to germination; Heschel et al, 2007). However, in the absence of cold, CBF levels are generally higher in developing seeds than in seedlings, a conclusion also supported by available microarray data.…”

“…Two phytochrome isoforms, phyB and phyE, were both downregulated by low temperature. Both of these are important for dormancy and germination (Heschel et al, 2007), and this suggests that more dormant seeds might desensitize their germination to light via the inhibition of phytochrome transcription. Genes involved in ABA signaling in general showed an increase in expression at the warmer temperature, although these changes were in general only twofold or less and are expected to be much less important than the large difference in CYP707A2 expression and the magnitude of the effect of ABA on their protein levels.…”

Tissue- and isoform-specific phytochrome regulation of light-dependent anthocyanin accumulation in Arabidopsis thaliana

“…Prior reports have established roles for phyE in germination 52 and temperature-dependent aspects of germination, 53 the regulation of internode elongation and flowering time, 32 and temperature-dependent regulation of flowering. 54 Thus, in addition to expanding our knowledge on the distinct roles of phy family members in the regulation of light-dependent anthocyanin accumulation, we have provided significant new insight into the function of phyE in Arabidopsis.…”

Contrasting germination responses to vegetative canopies experienced in pre- vs. post-dispersal environments

“…Active phytochrome (Pfr) is involved in lightstimulated germination (Whitelam and Devlin, 1997;Heschel et al, 2007). FR light converts phytochrome from its active (Pfr) to inactive (Pr) form, and R light converts Pr to bioactive Pfr.…”