Embargo: 23:00 Beijing Time, 2 April, 2020
Branching allows plants to occupy space in 3D, an innovation consider essential for their adaption. Branching requires reestablishment of new growth axes, which depends on stem cell activities. Where do these stem cell come from?
A team led by investigators from the Institute of Genetics and Developmental Biology (IGDB), Chinese Academy of Sciences is reporting a self-activation loop that maintains stem cell fate in the leaf axil to enable branching.
The findings, published in Current Biology on April 4, 2020, show how a key shoot stem cell promoting gene activates its own expression to maintain a stem cell lineage in the leaf axil to enable branching. This knowledge could help researchers to optimize crop architecture to further boost yield, especially in an era of global climate change.
Distinct from animals, plants form lateral organs throughout their life from a specialized stem cell-containing tissue, termed meristems. Shoot apical meristems form leaves, and buds establish at the leaf axil to enable branching. Buds are formed by axillary meristems that have the same developmental potential as the shoot apical meristem. Previous research by the same group of scientists has showed that a meristematic cell lineage is maintained in the leaf axil to provide progenitor cells for axillary meristem initiation. This current study reports how cell fate is maintained in this cell lineage.
"Meristematic cells use a very simple mechanism to keep their identify,” said Professor JIAO Yuling, corresponding author of the paper. “This research helps us to understand how cell fate can be maintained, and this regulatory circuit may also be utilized by animal stem cells.”
The leaf axil meristematic cells maintain the expression of STM, a transcription factor promoting shoot meristems. The scientists found that the maintenance of STM expression relies on its self-activation: STM binds to its own promoter and activates gene expression. STM is not alone, and this process requires a STM-interacting partner protein ATH1. ATH1 and STM split the job. Whereas ATH1 is responsible for DNA binding, STM provides transcriptional activation activity. In addition to the new roles of ATH1 in axillary meristem initiation, a previous study by Professor Robert Sablowski, a coauthor and Research Group Leader at John Innes Centre (JIC), found it regulates plant height.
Why the expression of STM needs to be maintained? "STM expression is required to keep the STM locus accessible to other binding proteins." said first author CAO Xiuwei, a postdoctoral fellow in JIAO's lab. "The STM locus needs to be bound by other transcription factors before axillary meristem initiation, and this binding requires a permissive epigenetic environment."
Comparing with animals, plant cell fate is more flexible. Nevertheless, developmental history of plant cells is also important. Recent studies have shown that cell lineages are essential in many aspects of development, ranging from branching to stomata formation, lateral root formation, and regeneration. “Plant cells do not migrate, providing a more tractable system to study cell lineage and fate determination.” JIAO added. This study inspires future investigation into understanding the molecular mechanisms underlying stem cell fate maintenance in plants and in animals.
Image: A self-activation loop that maintains leaf axil cells with a meristematic cell fate. ATH1–STM heterodimer binds the STM locus to maintain its expression. The maintained expression endows permissive STM chromatin for subsequent upregulation. This auto-regulation safeguards the re-establishment of stem cell niche for branching. (Image by IGDB)
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In addition to Cao, Jiao, and Sablowski, the research team includes: IGDB's current and formal WANG Jin, XIONG Yuanyuan, YANG Haibian, YANG Minglei, and YE Peiyi, JIC’s Stefano Bencivenga.
CITATION: Cao, X., Wang, J., Xiong, Y., Yang, H., Yang, M., Ye, P., Bencivenga, S., Sablowski, S. and Jiao, Y. (2020) A self-activation loop maintains meristematic cell fate for branching. Current Biology, DOI: xxx
The research was supported by the National Natural Science Foundation of China (grants 31825002, 31861143021, and 31861130355), the Key Research Project of the Frontier Science of CAS (grant ZDBS-LY-SM012), the Strategic Priority Research Program of CAS (grant XDA24020203), a Newton Advanced Fellow of the Royal Society (grant NAF\R1\180125), and CAS-JIC Centre of Excellence for Plant and Microbial Science.
