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Plants, despite their ability to root deeply into the ground and reach for sunlight, are ultimately stationary organisms that must withstand various environmental challenges including fluctuating temperatures, drought, and microbial threats. To mitigate these risks, many plant species have developed protective adaptations, one of which is the formation of a specialized outer layer called the periderm. While much research has focused on the early stages of plant development, the later-stage formation of periderm has been less explored until recently.
Researchers at the Salk Institute have introduced a groundbreaking gene expression atlas that maps the plant periderm at a single-cell level. This atlas reveals crucial insights into the cellular composition of the periderm and highlights the genes and biological processes that guide its development. Among these are phellem cells, which are enriched with suberin – a molecule that plays a vital role in capturing and storing carbon from the atmosphere over extended periods. This enhanced understanding could enable scientists to promote the growth of this protective layer in plants, particularly in the face of climate change-induced stress. Additionally, it opens avenues to enhance the genes associated with phellem cell production, potentially resulting in plants better equipped to sequester carbon, aligning with the objectives of Salk’s Harnessing Plants Initiative.
The findings of this research were published in Developmental Cell on January 9, 2025.
According to Professor Wolfgang Busch, the lead author of the study and director of the Harnessing Plants Initiative at Salk, “Plants are essential in removing carbon from the atmosphere and storing it in the soil. The periderm, particularly its phellem cells, facilitates the storage of carbon in a stable form. By thoroughly mapping the process of how these cells develop, we can gain a better understanding and encourage the synthesis of durable carbon storage in plant roots, thus fostering resilience against climate change.”
When plants initially establish themselves, they focus on primary growth characterized by extending root length. As they mature, they shift to secondary growth, which involves thickening existing roots and developing the periderm. This layer comprises various cell types including phellem, phellogen, and phelloderm, each performing unique functions and influenced by distinct genetic profiles, aspects which have largely been underexplored in prior research.
The research team was particularly interested in the phellem cells for their high suberin content. Suberin is significant in the context of the Harnessing Plants Initiative as its integration in plant roots can provide a stable carbon reservoir compared to other parts of the plant where carbon may dissipate quickly. In addition to its role in carbon storage, suberin has been associated with enhanced resistance to root rot, suggesting a dual role of protection and carbon sequestration for these cells.
Previous studies on periderm structures primarily utilized bulk analysis techniques that, while informative, did not capture the specificity of individual cell types. To address this, the Salk research team employed cutting-edge single-cell sequencing methods, thereby allowing for detailed insights into the unique genetic make-up of each periderm cell type. They concentrated on the model plant Arabidopsis thaliana, commonly used in plant biological research, to monitor gene expression throughout the development of its root cells.
“This level of detail regarding mature plants over time is unprecedented,” remarked Charlotte Miller, a research scientist in Busch’s lab and the first author of the study. “While previous methodologies analyzed entire root systems, single-cell techniques enabled us to dissect the genetic development of each individual cell in the periderm, fostering greater precision in engineering resilient plant species capable of addressing climate change challenges.”
The study unveiled a multi-phased developmental pathway for phellem cells, identified by critical genes such as MYB67 that are integral to regulating this process. By understanding the genetic profiles at various developmental stages, researchers aspire to identify genes that could be harnessed to enhance the production of phellem cells and increase their suberin content, thereby bolstering carbon capture capabilities.
Furthermore, the atlas yielded valuable insights into other periderm cell types beyond phellem, facilitating a clearer understanding of developmental transitions within the periderm system, such as the transformation of phellogen into phellem cells. Miller expressed particular enthusiasm for investigating phellogen cells, noting their unexpected capacity to differentiate into various cell types even during later stages of plant growth.
Busch anticipates that the knowledge of suberin-rich cells may illuminate how they effectively seal wounds created by lateral root growth – a process that often compromises the integrity of the plant’s outer layer. Learning more about the relationship between periderm cell types and suberin content could lead to better insights into this complex dynamic, which is critical for root expansion while minimizing susceptibility to infections.
In conclusion, Busch emphasized that this research not only advances scientific understanding of plant biology but also paves the way for developing stronger crops capable of enhancing carbon sequestration, addressing both agricultural productivity and climate change mitigation, key tenets of Salk’s Harnessing Plants Initiative.
Other contributors to this study include Sean Jarrell-Hurtado, Manisha Haag, Y. Sara Ye, Mathew Simenc, Paloma Alvarez-Maldonado, Sara Behnami, Ling Zhang, Joseph Swift, Ashot Papikian, Jingting Yu, Kelly Colt, Joseph Ecker, Todd Michael, and Julie Law of Salk.
This study received support from the Bezos Earth Fund, Hess Corporation, and TED Audacious Project.
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