The “Fertilization Dance” in Flowering Plants is Similar to Animals….Except for Who Leads

55218307 86bfa9d7a6 zThe Sperm & Egg Tango

In a paper published in the 23 November 2012 issue of Science magazine (Ref 1 below), Dr. Stephanie Sprunck and Prof. Dr. Thomas Dresselhaus and colleagues report a major finding regarding the cellular nature of sexual reproduction in plants.

Specifically, they have been studying gamete interaction during fertilization in the flowering plant Arabidopsis thaliana.

Briefly, what they report in this paper is “…that plants do the fertilization dance similarly to animals, but with a twist.” (from Ref 2 below)

From an excellent summary of the paper provided by Dr. William J. Snell (Ref 2 below), the major findings of this paper are as follows:

“In animals, the egg remains quiescent until fused with the sperm, but in Arabidopsis the egg leads. The egg cell responds to sperm discharged from a newly arrived pollen tube by secreting a cloud of sperm-activating proteins. The aroused sperm redistributes a previously cryptic putative membrane fusogen to its plasma membrane to prepare for fusion.”

These researchers also reported that, unlike in animal fertilization in which only the sperm is activated before fusion with the egg, in Arabidopsis both gametes are activated before fusion.

“Thus, the mutual activation of Arabidopsis gametes before fusion points to an evolutionary link between flowering plant fertilization and fertilization in unicellular sexual reproducing organisms such as yeast and Chlamydomonas….” (from Ref 1 below)

F1 large

Fertilization across phyla. As in algae and animals, Arabidopsis gametes undergo mutual activation. Upon sperm arrival, the egg cell secretes EC1 proteins that trigger sperm to display previously cryptic HAP2. Adhesion between Chlamydomonas gametes also triggers exposure of cryptic HAP2, and in mammals, sperm binding to egg triggers exposure of Izumo-1. Only in the two plant systems are both gametes activated before fusion. (Please Note: This figure and the accompanying legend are from Ref 2 below.)

References

1. Sprunck, S., et al. (2012) “Egg cell–secreted EC1 triggers sperm cell activation during double fertilization.” Science, Vol. 338, pp. 1093-1097. (Abstract)

2. Snell, W.J. (2012) “Plant gametes do fertilization with a twist.” Science, Vol. 338, pp. 1038-1039. (Summary)

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