Power struggle between genetic master switches decides growth orientation in plants

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Washington, March 1 (ANI): A new research has determined that the power struggle between genetic master switches in plants decides the fate of their stem cells and the orientation of their growth.

Researchers at the Salk Institute expose the turf wars between two groups of antagonistic genetic master switches that set up a plant's polar axis with a root on one end and a shoot on the other.

"In what is arguably the most important decision for a plant, setting up the root/shoot axis, occurs during the early embryonic stages," said the study's lead author Jeffrey A. Long, an assistant professor in the Plant Molecular and Cellular Biology Laboratory.

"A tightly controlled balancing act between two groups of transcriptions factors ensures that they stay where they belong and don't get into each other's way," he said.

Plant embryogenesis establishes a very simple structure that contains two stem cell populations.

The shoot meristem, which will give rise to all the "above-ground" organs such as the stem, the leaves and the flowers, and is the site of photosynthesis; and the root meristem, which gives rise to the root system, which lies below the ground and provides water and nutrients to the plant.

While investigating why a defective TOPLESS gene messes with a plant's basic architecture, Long and his team discovered functional TOPLESS codes for a repressor protein that inactivates genes that otherwise would cause root development in the shoot area of the plant.

In the current study, Zachery R. Smith, a graduate student in Long's laboratory, discovered that these fate-transforming genes are actually two familiar characters: the genes PLETHORA 1 and 2 had been known to act as master regulators that determine the identity of the root meristem.

"Without TOPLESS to keep them turned off, however, these two transcription factors are free to impose their will on the top half of the plant embryo causing the development of a second root instead of a shoot," explained Smith.

Trying to unearth the missing master regulators of shoot development, Smith searched trough tens of thousands of mutant plants, till he hit on a member of the CLASS III HD-ZIP transcription factors, known as PHABULOSA, that fit the bill.

When the Salk researchers forcefully expressed members of the CLASS III HD-ZIP family in the traditional territory of the PLETHORA duo, it transformed the root into a shoot, resulting in a seedling with leaves on both ends.

"Although it had been known that HD-ZIPs are involved in many aspects of plant polarity nobody had ever shown that they can transform a root pole into a shoot pole," said Long. (ANI)

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