Once Jackson's team had proven the necessity of chaperonins in KN1 trafficking, they set their sights on revealing the "how" and "why" of the relationship. In a series of experiments involving maize and Arabidopsis, a mustard plant used widely as a model for genetics research, they confirmed, first, that the entire chaperonin machinery a protein mega-complex consisting of eight segments, or subunits is involved in cell-to-cell trafficking of KN1.
"We could then ask questions about the mechanism involved, and about the functional importance of this trafficking to the plants," says Jackson. Through an ingenious process of elimination, he and his colleagues performed experiments showing that a portion of the chaperonin complex, called CCT8, had to be present in the "destination" cell if KN1 trafficking was to occur normally. "We inferred from our results that the chaperonin performs its role in the trafficking by refolding KN1 proteins in the destination cell. In other words, KN1 travels through the channel in a partly unfolded state."
Even more important, the team concluded that by selectively transporting KN1 and other "mobile signals" using this mechanism, plants are able to establish and maintain populations of stem cells. As Jackson's prior work has shown, this occurs, for instance, in meristems, the stem cell-rich tips of plants where new growth takes place.
Why do the signals that maintain stem cells need to be mobile? "Development is all about communication," Jackson explains. "Cells talk to each other, among other things, to influence one another. We hypothesize that the trafficking of signals like KN1 could serve to establish protein concentration gradient
|Contact: Peter Tarr|
Cold Spring Harbor Laboratory