August 26, 2009 | David F. Coppedge

Plants Use Hourglass Mechanism

Plants need to know when to flower and produce seed.  They can read the sunshine, but what about plants living in shade or cloudy conditions?  It turns out they have two mechanisms for telling time: a light meter and an hourglass.  If the light meter doesn’t switch on, the hourglass lets the plant know it had better flower while it still has a chance to make seed.
    Science Daily reported on work by the Max Planck Institute for Developmental Biology, published in Cell.1  The way the hourglass works is through micro-RNAs.  By binding to messenger RNAs destined to start flowering processes via SPL proteins, they inhibit their actions.  “Jia-Wei Wang and colleagues demonstrate that independent of external cues, the concentration of the microRNA declines over time, like sand running through an hourglass,” the article explained.  “When the microRNA concentration falls below a certain level, enough SPL proteins are produced to activate the flowering process even in the absence of other regulators that measure day length or external temperature.”
    The two mechanisms provide redundancy for the plant to ensure flowering.  “The redundancy of environment-dependent and �independent mechanisms ensures that plants do not wait forever until flowering,” Max Plank director Detlef Weigel explained.  “Better flower once, then never.”
    Neither the Max Planck press release nor the scientific paper mentioned evolution once.


1.  Wang, Czech and Weigel, “miR156-Regulated SPL Transcription Factors Define an Endogenous Flowering Pathway in Arabidopsis thaliana,” Cell, Volume 138, Issue 4, 738-749, 21 August 2009, doi:10.1016/j.cell.2009.06.014.

Micro-RNAs were only discovered in the last decade.  This is another example of them in action with a functional regulatory role.  Darwinians will undoubtedly have a tall tale ready to explain this, but systems biology, which sees an organism as a system of interrelated and coordinated parts (see 07/21/2009), needs Darwinian storytelling like a teenage face needs a zit.

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