In a laboratory at Tokyo University of Science in Japan, a common liverwort is quietly rewriting what scientists understand about how plants build themselves. The moss-like plant, Marchantia polymorpha, has only two genes responsible for producing reactive oxygen species (ROS) signaling molecules—compared to the dozens found in most other plants. This simplicity made it the perfect model for a research team seeking to understand a fundamental question in plant biology: how do plants organize billions of cells into structured roots, stems, and leaves?
Led by Professor Kazuyuki Kuchitsu from the Department of Applied Biological Science, the team used CRISPR-Cas9 gene-editing to disrupt both of those genes simultaneously. What happened next revealed just how critical these signaling molecules are. When both genes were disabled, the plants didn't develop normally at all. Instead of forming organized tissues, they became what researchers described as a slowly growing, disorganized cell mass—almost like a callus, the kind of undifferentiated tissue that forms on wounded plants.
The study, published in Current Biology, showed that ROS produced by these enzymes—known as NADPH oxidases or RBOHs in plants—acts as a crucial organizing signal for cell division. Plants with only one of the two genes disrupted showed abnormal growth patterns, but losing both created severe developmental defects. Reduced RBOH activity led to fewer actively dividing cells in the growing regions of the plant, and chemically removing ROS produced the same growth problems, confirming that ROS signaling is essential for normal vegetative growth.
But the role of these molecules extended beyond just getting cells to divide. In mutants lacking RBOH function, the developing cells were abnormally swollen and irregular, lacking the spatial order needed to form organized tissues. The researchers found that RBOH-derived ROS signaling is vital for maintaining the integrity of the cuticle—the waxy protective layer on plant surfaces—and the cell wall. When this protection broke down, cell-wall components leaked outside the plant body.
The team combined genetic approaches including conditional knockout and knockdown analyses with live-cell imaging, electron microscopy, and comprehensive gene expression analysis. That analysis revealed that ROS signaling is closely tied to hormone-related gene expression and transcriptional programs that guide cell differentiation—essentially the instruction sets that tell cells what to become as the plant develops.
The findings open new avenues for understanding plant development and could eventually inform agriculture. By clarifying how ROS signaling interacts with hormone pathways and cell differentiation programs, researchers gain insight into the basic mechanisms that shape all plant life.