Plant researchers have discovered a protein whose role in regulating cell differentiation and sex determination in vascular plants was previously unknown, using a fern model for their studies. This finding sheds light on the process of stem cell proliferation, which is vital for the reproduction and continuation of species, as it prevents all offspring from becoming male.
Researchers at Purdue University have identified a protein that has an unrecognized function in managing cell differentiation and defining gender in vascular plants, through investigations involving a fern model. This important discovery offers new perspectives on the stem cell proliferation process, which plays a crucial role in reproduction and species survival by ensuring not all descendants develop as males.
Yun Zhou, an associate professor in botany and plant pathology, along with a team of five Purdue colleagues, recently shared their findings in Current Biology. Their research focused on Ceratopteris, a fern species commonly used in botanical research, to unveil essential mechanisms that govern stem cell proliferation at cellular and molecular levels. In plants, stem cells that haven’t differentiated are present in actively growing regions called meristems.
The researchers found that a gene known as CrHAM is linked to a vital process that is present in all plants, animals, and humans—stem cell proliferation. All these multicellular organisms carry undifferentiated stem cells.
“Undifferentiated cells have the capability to divide and provide cells that eventually develop into various organs,” Zhou explained. “This is why it is crucial to maintain the stem cell population and develop meristems for plant growth and reproduction.”
Even though plant scientists already understood that stem cells are essential for plant growth and development, Zhou elaborated, “our research shows that CrHAM regulates meristem indeterminacy, highlighting its primary role in preventing stem cells from differentiating.”
This fern species can evolve as either male or hermaphrodite. Hermaphrodites feature both male and female reproductive parts and develop and maintain a meristem. In contrast, males do not form meristems. The findings in Current Biology pinpoint CrHAM as a critical factor that stops meristem tissues within hermaphrodites from producing male organs. Without this regulatory mechanism, meristem tissues would consistently differentiate into male organs, resulting in the loss of the hermaphrodite identity and halting reproduction for the species.
To gather data and validate their hypotheses, Zhou’s team utilized a blend of thorough molecular genetic analysis, comprehensive genome-wide expression profiling across various sex types and genotypes, and quantitative live-imaging confocal microscopy to analyze cell division. This method, innovated in Zhou’s lab, allowed researchers to monitor individual cells in the Ceratopteris fern as they divide and differentiate into distinct organs while preserving the plant’s normal growth.
Findings from previous research using this technique were published in a 2022 paper in Communications Biology. The lead author of both the Current Biology and Communications Biology studies was Yuan Geng, a PhD graduate from Purdue’s Zhou lab, now serving as a postdoctoral scholar at Caltech.
This Current Biology study is the latest in a progression of findings from Zhou and his team following his arrival at Purdue. Zhou aims to explore the cellular and molecular strategies that plants utilize to maintain stem cell division and promote organ formation. The balance of these processes in multicellular organisms raises numerous questions.
“In my lab, we’ve established two model systems to explore these questions,” Zhou mentioned. One model is the fern Ceratopteris—a non-seed plant. The other is the shoot meristem of Arabidopsis, a model for flowering plants. In related Arabidopsis studies on stem cells and HAM family genes published in Science in 2018 and Nature Communications in 2020, Zhou’s team uncovered regulatory principles that could be harnessed to enhance shoot meristem function and boost crop production.
While Zhou’s investigation doesn’t specifically target agricultural crops, the insights gained could contribute to improving biomass for energy and increasing food production yields. Additionally, a deeper comprehension of stem cell dynamics may eventually aid human health through regenerative therapies or stem cell-derived organs.
“All these areas are intricately linked to the foundational mechanisms of stem cell division and differentiation,” Zhou stated. “The essential knowledge we gain from this model system can certainly be leveraged to enhance quality of life.”
As vascular plants, both ferns and seed plants transport water and nutrients using specialized tissues. However, ferns reproduce through spore production, not seeds like seed plants.
Ferns and seed plants split into different lineages hundreds of millions of years ago, and throughout this extensive period, the HAM gene family has still worked to keep meristem cells undifferentiated.
“Though these genes in various plant species sometimes interact with different signaling pathways, they ultimately work toward the same goal at cellular and developmental levels. This is somewhat unexpected and opens new inquiries for our ongoing research,” Zhou expressed.
This research was supported by the National Science Foundation (NSF). Zhou’s team’s stem cell studies involving plant models are currently funded by both the NSF and the National Institutes of Health.
