Abstract:
Biological rhythms are ubiquitous. They can be generated by circadian oscillators,
which produce daily rhythms in physiology and behavior, as well as by developmental oscillators
such as the segmentation clock, which periodically produces modular developmental units. Here,
we show that the circadian clock controls the timing of late-stage
floret development, or anthesis,
in domesticated sunflowers. In these plants, up to thousands of individual florets are tightly packed
onto a capitulum disk. While early floret development occurs continuously across capitula to
generate iconic spiral phyllotaxy, during anthesis floret development occurs in discrete ring-like
pseudowhorls with up to hundreds of florets undergoing simultaneous maturation. We demonstrate
circadian regulation of floral organ growth and show that the effects of light on this process
are time-of-
day
dependent. Delays in the phase of floral anthesis delay morning visits by pollinators,
while disruption of circadian rhythms in floral organ development causes loss of pseudowhorl
formation and large reductions in pollinator visits. We therefore show that the sunflower circadian
clock acts in concert with environmental response pathways to tightly synchronize the anthesis of
hundreds of florets each day, generating spatial patterns on the developing capitulum disk. This
coordinated mass release of floral rewards at predictable times of day likely promotes pollinator
visits and plant reproductive success.
Description:
DATA AVAILABILITY : All source data have been uploaded to Dryad under the following accession codes: 10.25338/B8865X
(timelapse scoring), 10.25338/B86358 (pollinator visits), 10.25338/B8963G (consensus scoring),
10.25338/B8CW5R (ovary measurements), and 10.25338/B8HP9F (organ growth kinetics).