The researchers now show that Short-root moves from cells in the plant's inner vasculature out into the waterproofing endodermis that surrounds it to activate Scarecrow. Together, those two transcription factors (genes that control other genes) activate microRNAs, known as MIR165a and 166b. Those microRNAs then head back toward the vascular cells, meeting and degrading another transcription factor (called Phabulosa) as well as other regulatory factors along the way.
"Dr. Benfey and his colleagues have shown how two modes of gene regulation work together across cellular borders to ensure the proper patterning of plant root tissues," said Susan Haynes of the NIH's National Institute of General Medical Sciences, which partially funded the study. "This study provides important insight into how cells communicate positional information to orchestrate the complex process of tissue and organ development."
"Now we know that microRNAs can and do move to form gradients in the context of plant development," Benfey added. "It adds a new dimension to gene regulation."
According to Benfey, history suggests this kind of two-way communication involving microRNAs in the developing root is likely to be a more general phenomenon. "Just about everything in biology that once seemed particular sooner or later proves to be more general," he said.
He said there's also reason to think that the specific regulatory interactions they've uncovered were key in the evolutionary transition from single-celled algae to land plants.
"Formation of vascular tissue with a surrounding endodermal layer that acts as waterproofing was a key milestone in the evolution of land plants," Benfey said. "Without a tube to conduct water, you can't grow a tree or a sunflower."
|Contact: Kendall Morgan|