Breakthrough of the Year: The Runners-Up
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This year''s runners-up for Breakthrough of the Year include new gamma-ray observations, the long-sought receptor for a key plant hormone, mock monopoles, a drug that increases life span, ice on the moon, gene-therapy successes, insights into the properties of graphene and how to use it to make novel devices, Hubble''s rebirth, and the first x-ray laser.
ABA Receptors
See references and Web links on plant ABA receptors.
Although "Fight or Flight" is not in their behavioral repertoire, plants have their equivalent of an adrenaline rush: a chemical called abscisic acid (ABA). High concentrations of ABA keep seeds dormant and help curtail water loss and inhibit root and other vegetative growth when times are tough. The receptors for this key plant hormone have long eluded plant biologists, sending them down false trails and leaving research in disarray. But in May, two independent teams, taking different approaches, identified the same family of proteins as the receptors. By late fall, several other groups had confirmed the connection between ABA and the PYR/PYL/RCAR proteins. As one leader in the field put it: "The ABA receptor field finally has a success."
One team, based in Germany, homed in on these receptors by looking for proteins that bind to enzymes called ABI1 and ABI2, known to help spur ABA activity. They found two, calling each a "regulatory component of ABA receptor" (RCAR). A second team, based in California, tracked down an ABA receptor by figuring out what pyrabactin, which revs up ABA activity, interacts with. This group called the receptor PYR1. Both teams discovered that their receptors were part of the same 14-member protein family.
Other researchers from China, Japan, Europe, and the United States have supported these results. Several have obtained crystal structures of ABA bound to its receptor or ABA and the receptor interacting with the PP2C phosphatases that must be shut down to allow ABA to function. The structures show that PYR/PYL/RCAR proteins pair off, making a gated pocket that ABA nestles into. ABA changes the shape of the pair of molecules so that the "gate" closes and creates a binding surface for a PP2C.
These results are a boon for plant biology?and possibly beyond. The PP2C and the ABA receptors both belong to highly conserved families of proteins whose roles in other organisms may become clearer now that their function in plants has been nailed down.
See references and Web links on plant ABA receptors.
To view the article''s source, visit Science Magazine online.
