A paper by Myles Fenske (Imaizumi Lab) and colleagues recently was featured on the cover of PNAS. Read more about their research on the timing of Petunia fragrance below.
When most people think of circadian clocks, they think of jet lag, and… well, just jet lag1. Circadian clocks are in need of an awareness campaign. Even accomplished life scientists are guilty of asking the question: “plants have clocks?2”. Indeed they do, as does most every organism on Earth. Yes, even bacteria.
Turns out, being able to synchronize internal and external physiology with the rotation of the Earth is kind of a big deal. The early bird gets the worm, and to be the early bird, you gotta have an alarm clock.
Clocks are incredibly effective at timing behavior because of how pervasive they are in regulating physiology. A recent study showed that upwards of 30% of the plant genome (specifically Arabidopsis) is under circadian clock control3. Clocks don’t just regulate physiology at a single point of contact, they exert an influence over the entire organism.
There are some pretty interesting behaviors that the clock regulates; you may have seen the famous sun-tracking sunflower video. Back in the summer of 2011, I was reading Stacey Harmer’s excellent review of the plant circadian clock4, when I came across a paragraph listing a few other outputs of the clock: “photosynthesis, stem growth, and scent emission”. Scent emission, huh?
In fact, many flowering plants emit scent only at specific times of day, which corresponds with the activity of their most helpful pollinators. Our study organism, the common garden Petunia (Petunia hybrida), emits scent at night. Petunia hybrida’s parent, and “wild analog5”, Petunia axillaris, also emits scent at night, which attracts the attention of the large hawkmoth Manduca sexta.
While scent emission was already known to exhibit circadian rhythms, virtually nothing was known about the circadian clock’s connection to scent emission.
To make a long story short, in this paper, we identify Petunia hybrida’s LHY, the first identified clock gene in Petunia, and we then change its temporal expression pattern, and examine how that change in expression affects scent emission. When LHY is expressed constantly (during both day AND night) scent emission completely ceases! If you look at the underlying gene expression, many of the scent metabolic genes are repressed to the point that they no longer have evening peaks.
When we shifted the expression of LHY from its usual morning peak to the early afternoon, we saw a corresponding shift in scent emission, as well as seeing a shift in scent gene expression from the evening to the early afternoon. We also showed that LHY protein is able to directly bind to scent gene promoter sequences in vitro.
It appears that LHY primarily contributes to the timing of scent emission not by regulating the expression of enzymes directly responsible for producing scent, but those responsible for producing the precursor substrates.
Check out our paper and some of the press links (ranging from Nature to creationist bloggers6!) at:
- Or Taco Time®.
- First hand experiences
- Covington MF, et al. (2008) Global transcriptome analysis reveals circadian regulation of key pathways in plant growth and development. Genome Biol 9(8):R130
- Harmer SL. (2009) The circadian system in higher plants. Annu Rev Plant Biol 60:357–377.
- I may have made up this term. The research model for the common garden petunia, P. hybrida, is a cultivar named “Mitchell”. It’s a hybrid of P. axillaris and P. integrifolia. P. axillaris has large white flowers with long and narrow corolla tubes (which require long proboscises, unless you’re a nectar robber) and is largely pollinated at night when it emits a strong bouquet of scent. P. integrifolia has purple flowers with short and wide corolla tubes (which facilitate bumble bee visitation during the daytime). P. hybrida most closely resembles P. axillaris, with white flowers emitting a P. axillaris-like scent profile at night, and is readily pollinated by Manduca sexta in Tom Daniel’s windtunnel. Why not do this study in P. axillaris? Because the metabolic pathways were characterized in P. hybrida, the economically significant species.
- This is why you don’t move the phylogeny to the supplement.
