Biologists Unlock Secrets of Plants' Growing Tips

Aug 25, 2009

(PhysOrg.com) -- Biologist Magdalena Bezanilla and colleagues at the University of Massachusetts Amherst have used a technique they call multi-gene silencing to, for the first time, simultaneously silence nine genes in a multicellular organism. It allowed them to discover molecular secrets of how certain plant tissues know which end is their growing tip, also referred to as polarized growth.

The biologists conducted these experiments in a moss, but the findings illuminate processes in two tissues—root hairs and —found in all seed plants. Root hairs are extremely fine individual cells that grow out of a plant’s root, greatly increasing its surface area to collect water, essential minerals and nutrients. Pollen tubes travel down the flower to fertilize the plant’s egg. Scientists have “a very limited knowledge” at the molecular level of how such cells determine the direction they’re growing, says Bezanilla.

Knowing how to interrupt pollen tube formation in plants such as corn and soybeans, for example, could help prevent genetically engineered crops from interbreeding with wild populations. Aiding root hair growth could boost drought-resistance to other economically important plants.

Bezanilla and colleagues’ research paper in a recent issue of describes their work in the Physcomitrella patens moss species, which provides a simple, fast-growing model plant. Conveniently, it has a developmental stage when all cells are undergoing tip growth. Another advantage is that its whole genome is known.

The researchers focused on two proteins, actin and forming. Actin, in this case a kind of scaffold-builder needed to form root hairs and pollen tubes, forms filamentous polymers and is important for many cellular processes in species ranging from yeast to man. Formins, like actin, are found in many species and help to control actin polymer formation. Formins are critical for actin-based cellular processes.

Tools in a biologist’s kit can now remove the function of specific proteins—usually one or two at a time—to silence a gene, but in this study the researchers succeeded in silencing a remarkable nine genes at one time. Bezanilla and colleagues systematically silenced the many actin-regulating formins and determined which members of this protein family are needed to generate cells for proper tip growth.

As for silencing nine genes at once, Bezanilla says, “It can be difficult to identify the function of a single gene when it is nested in a highly redundant system or family where another family member will simply step in and take over performing a similar or overlapping function for the one that’s missing.” By using their technique for multi-gene silencing, she adds, “we discerned how to silence the whole family and dissect gene function in that wider context.”

Other tools in the researchers’ kit are methods for re-introducing the silenced genes, either normal or modified versions, the biologist explains. By “swapping parts” from closely related formin proteins and measuring tip growing activity for each combination, her research group eventually concluded that only one intact subclass of formins drives normal growth and controls how the plant recognizes its growing tip. “If you take away any part of the formin, tip growth stops,” says Bezanilla.

Interestingly, the researchers also discovered that this particular subclass of formins is the fastest yet known in any organism. “What’s interesting here is that these mosses don’t grow very fast in nature,” Bezanilla comments. “So we don’t understand why it would need the fastest formin, but it could be that what the plant actually needs at its growing tip is the ability to be flexible and dynamic, that is, adapt quickly to whatever situation is encountered,” she adds.

This required collaboration with biochemist Laurent Blanchoin and colleagues at the University of Joseph Fourier, Grenoble, France. Bezanilla says this teamwork combining in vitro and in vivo studies in a single work “is really the future of where science should be going because as important as it is to know the biochemical function of a particular protein molecule you’re studying, knowing its role in the whole organism is even more important.”

“Finding out that one protein gets its tasks done twice as fast as another in a test tube is interesting, but this difference could be meaningless to a cell,” she explains. “Marrying the in vivo and in vitro approaches is critical to our full understanding of biological processes.”

More information: Proceedings of the National Academy of Sciences

Provided by University of Massachusetts Amherst (news : web)

Explore further: Study finds fish just wanna have fun

add to favorites email to friend print save as pdf

Related Stories

A budding role for a cellular dynamo

Feb 18, 2009

Actin, a globular protein found in all eukaryotic cells, is a workhorse that varies remarkably little from baker's yeast to the human body. Part of the cytoskeleton, actin assembles into networks of filaments that give the ...

2-protein team would be lost without each other

Apr 19, 2007

Just as a hard-charging person sometimes needs a calming partner to be more effective, so it is with a pair of critical proteins that promote cell division and growth in the rapidly expanding root tip of plants.

How actin networks are actin'

Jan 02, 2008

Dynamic networks of growing actin filaments are critical for many cellular processes, including cell migration, intracellular transport, and the recovery of proteins from the cell surface. In this week’s issue of the open-access ...

How roots find a route

Feb 28, 2008

Scientists at the John Innes Centre in Norwich have discovered how roots find their way past obstacles to grow through soil. The discovery, described in the forthcoming edition of Science, also explains how ...

Recommended for you

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

irjsiq
not rated yet Aug 30, 2009
Fascinating Article!

Especially in Vivo/in Virtro simultaneously studied and reviewed related to processes of 'tip growth'.

Long familiar with 'growing tips' in 'root hairs', and the function of symbiotic mycelia, an order of magnitude smaller in diameter then root hairs.

Mycelia, which also have 'growing tips', are able to grow through even smaller soil spaces, enabling a greater system of 'mining' nutrients and moisture from a vastly increased soil area and carrying these back to the plant root system.

A phenomena of Saguaro Cactus, is the Saguaro's capability of very rapid root growth, in order to take fullest advantage of infrequent rains common to arid zones. The Saguaro's 'Ribs' expand with the 'drink' of water . . . saving the moisture for the perpetual 'lean times', when no rain falls!



Thanks again,

Roy Stewart,

Phoenix AZ