Both social and engineering factors must be further explored and scrutinized across the globe—as should notions of justice related to flooding impacts and responses.
Image courtesy of Shutterstock.com/Ekaterina Pokrovsky.
New Research In
Physical Sciences
Featured Portals
Articles by Topic
Biological Sciences
Featured Portals
Articles by Topic
Edited by Susan S. Golden, University of California, San Diego, La Jolla, CA, and approved May 29, 2018 (received for review March 30, 2018)
Significance
While all eukaryotic circadian clocks depend on transcriptional feedback loops, the plant circadian network is uniquely complex. An apparent redundancy in the plant clock is two types of transcription factors that antagonistically regulate common target genes. Here, we show that, although loss of either repressor- or activator-type factors perturbs clock pace and plant development, simultaneous loss of both types of factors restores near–wild-type development and largely rescues circadian period and phase phenotypes at ambient temperatures. However, in the higher-order mutant, rhythmic amplitude is reduced under optimal temperature, and rhythmicity is lost at low or high temperatures within the physiologically relevant range. Our data suggest that the multiple feedback loops of the plant clock help ensure rhythmicity under adverse environmental conditions.
Abstract
Although circadian oscillators in diverse eukaryotes all depend on interlinked transcriptional feedback loops, specific components are not conserved across higher taxa. Moreover, the circadian network in the model plant Arabidopsis thaliana is notably more complex than those found in animals and fungi. Here, we combine mathematical modeling and experimental approaches to investigate the functions of two classes of Myb-like transcription factors that antagonistically regulate common target genes. Both CCA1/LHY- and RVE8-clade factors bind directly to the same cis-element, but the former proteins act primarily as repressors, while the latter act primarily as activators of gene expression. We find that simulation of either type of loss-of-function mutant recapitulates clock phenotypes previously reported in mutant plants, while simulated simultaneous loss of both type of factors largely rescues circadian phase at the expense of rhythmic amplitude. In accord with this prediction, we find that plants mutant for both activator- and repressor-type Mybs have near-normal circadian phase and period but reduced rhythmic amplitude. Although these mutants exhibit robust rhythms when grown at mild temperatures, they are largely arrhythmic at physiologically relevant but nonoptimal temperatures. LHY- and RVE8-type Mybs are found in separate clades across the land plant lineage and even in some unicellular green algae, suggesting that they both may have functioned in even the earliest arising plant circadian oscillators. Our data suggest that the complexity of the plant circadian network may have arisen to provide rhythmic robustness across the range of environmental extremes to which plants, as sessile organisms, are regularly subjected.
Footnotes
- ↵1To whom correspondence should be addressed. Email: slharmer{at}ucdavis.edu.
Author contributions: A.S.-K. and S.L.H. designed research; A.S.-K. and R.W.K. performed research; V.F. contributed new reagents/analytic tools; A.S.-K., R.W.K., and S.L.H. analyzed data; and A.S.-K. and S.L.H. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1805524115/-/DCSupplemental.
Published under the PNAS license.
Log in using your username and password
Purchase access
You may purchase access to this article. This will require you to create an account if you don't already have one.
Multiple feedback loops of the Arabidopsis circadian clock provide rhythmic robustness across environmental conditions
More Articles of This Classification
Biological Sciences
Related Content
Cited by...
- No citing articles found.
Similar Articles
You May Also be Interested in
Blair Hedges discusses the state of Haiti's remaining forests and the consequences to biodiversity.
A study uncovers genetic evidence of early colonization of Jamaica by primates and suggests that adaptation can shape species morphology in novel environments, even when species come from morphologically conservative families.
Image courtesy of Lorraine Meeker (American Museum of Natural History, New York).
Researchers report that some moth species use sound absorbing-scales to avoid detection by bats and suggest that the findings could aid the design of biologically inspired sound absorbers for an array of applications, including noise mitigation and building acoustics.
Image courtesy of Thomas R. Neil.
Using phylogenetic analysis, researchers report that ants used plants for food and nesting long before plants evolved structures to accommodate arthropods, and although interactions with ants likely facilitated plant diversification, plant interactions did not shape ant diversification.
Image courtesy of Pixabay/cmolens.
