MicroRNAs (miRNAs), however, are short (~22) nucleotide RNA sequences found in plants and animals that do not encode proteins but act in gene regulation and in the process, impact almost all biological processes — from development to physiology to stress response.
Present in almost in every cell, microRNAs are known to target tens to hundreds of genes each and to be able to repress, or "silence," their expression. What is less well understood is how exactly miRNAs repress target gene expression.
Now a team of scientists led by geneticists at the University of California, Riverside has conducted a study on plants (Arabidopsis
) that shows that the site of action of the repression of target gene expression occurs on the endoplasmic reticulum (ER), a cellular organelle that is an interconnected network of membranes — essentially, flattened sacs and branching tubules — that extends like a flat balloon throughout the cytoplasm in plant and animal cells.
"Our study is the first to demonstrate that the ER is where miRNA-mediated translation repression occurs," said lead researcher Xuemei Chen, a professor of plant cell and molecular biology and a Howard Hughes Medical Institute-Gordon and Betty Moore Foundation Investigator. "To understand how microRNAs repress target gene expression, we first need to know where microRNAs act in the cell.
Until now no one knew that membranes are essential for microRNA activity. Our work shows that an integral membrane protein, AMP1, is required for the miRNA-mediated target gene repression to be successful. As AMP1 has counterparts in animals, our findings in plants could have broader implications."