Protein helps seeds get up and grow

BROWN (US) — An intricate network of proteins that regulates plant growth and development is key to how seedlings are able to push past the surface of the soil.

The universal role of the protein phosphatase 2A (PP2A), that operates in a variety of organisms, including humans where it is associated with tumor growth, is to cleave to a phosphoryl group off a protein to affect how it will function.

“Everybody has reversible protein phosphorylation,” says Alison DeLong, associate professor of biology at Brown University. “It’s a question of how an organism regulates the dephosphorylation reaction. You need to do that correctly in order to regulate growth correctly.”

Working with Arabidopsis thaliana speciments in her lab,  DeLong wanted to discover how PP2A regulates the production of ethylene, a gaseous hormone that inhibits the elongation of plant cells.

As a plant embryo germinates, cells in the emerging shoot elongate to reach above the soil. Its goal is to reach daylight so that photosynthesis can begin before the reserve of food in the seed runs out. PP2A’s job is to keep a lid on ethylene production during germination.

Details of the research are reported online in the journal PLoS Genetics.

“Keeping these ethylene levels low is actually quite critical during this phase of growth,” DeLong says.
In a series of experiments comparing normal A. thaliana plants to those with mutations that disabled PP2A and other proteins, DeLong and and graduate student Kyle Skottke, the lead author, found the mechanism by which PP2A works.

In seedlings, its phosphoryl-pruning effect suppresses the activity of a protein called ACS6 that is necessary to produce ethylene. In Petri dishes kept in the dark—analogous to growing underground—plants lacking a PP2A gene grew much shorter shoots than normal plants.

Unexpectedly, the team, including researchers from the University of North Carolina–Chapel Hill, also found that PP2A boosts the activity of a second class of ACS proteins. Those proteins are responsible for maintaining the normal baseline production of ethylene, which is important to have around at other developmental stages.

“For us the fun part of the story is that we went looking for the answer to a single question and then, in walking through the analysis to lead us to that single answer, we actually found a second phenomenon that we hadn’t known to look for,” she says.

A next step in DeLong’s lab will be to look at how the protein network operates during later developmental stages. With spring settled, so to speak, the growing season is the next focus of her inquiry into the nature of growth.

The National Science Foundation funded the research.

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