Longevity variation has been one of the fundamental research directions in the life sciences. On February 23, 2023, Plant Communications published online a review paper entitled "The imperial role of stem cells in determining plant longevity variation" by Omid Karami's team from Leiden University in the Netherlands and their collaborators. Starting from the long-term stability of plant stem cells, this review explains how plant stem cells regulate plant longevity in terms of genetic mechanisms, hormonal signaling and environmental factors.
The longevity of vascular plants ranges from a few weeks to several thousand years. Unlike animals, where most of their organs are usually formed during embryogenesis, vascular plants can achieve longevity in some species by proliferating stem cells located within the meristem to generate new tissues and organs both apically and laterally. Thus, plant stem cells make a significant contribution to longevity, and variation in plant longevity is largely determined by the persistence of stem cells and their maintenance of their daughter cell fate, and differentiation during organ formation. Although existing studies have provided a broad understanding of how plants maintain stem cell numbers, the factors that control stem cell maintenance are still poorly understood. Further understanding of the molecular genetic mechanism by which plants maintain stem cell fate for a long time will fundamentally unlock the secret of plant control of longevity.
Plant meristems mainly include shoot apical meristem (SAM), root apical meristem (RAM) and vascular cambium meristem (VCM). In plants, SAM is responsible for the formation of aboveground parts (stems, leaves, flowers, etc.); and the homeostasis of SAM is mainly regulated by CLV3 and their receptors (CLV1 and CLV2, etc.) and WUS transcription factors. The latest study found that FUL can shorten the lifespan of Arabidopsis by inhibiting the expression of WUS in SAM.
The maintenance of aboveground parts alone is not enough, and the maintenance of the plant root system is done by RAM. At the same time, RAM is regulated by various plant hormones such as auxin, cytokinin and ethylene, ROS and transcription factors such as ERF115, BRAVO and SCR.
VCM can form the xylem and phloem of plants; VCM is mainly regulated by the TDIF-PXY-WOX pathway. In addition, auxin, cytokinin, and ethylene act as positive regulators of cambial cell proliferation.
After germination, plants undergo the juvenile-to-adult transition and the vegetative-to-reproductive phase transition, respectively, during their growth and development. Genetic studies have shown that miR156/157 and its target gene SPL play an important role in the juvenile-to-adult transition, miR172 and AP2 family members are also involved in the formation of adult leaf traits. In addition, AHL15/19/20 are negative regulators of the juvenile-to-adult transition.
Physiological and genetic studies have shown that the vegetative-to-reproductive phase transition is comprehensively regulated by multiple endogenous and environmental factors, such as photoperiod, vernalization, age, and gibberellin biosynthesis and signaling. These processes are coordinated by a regulatory network of nearly 300 genes. These genes mainly include FLC, SOC1, FT, SPLs, CO, FD, AP1, and LFY.
Axillary meristems (AM) are located in the leaf axils of plants, and AM has the same cellular characteristics as SAM. AM is in a dormant state until it is induced by internal factors or environmental signals; after dormant axillary buds grow out, the formation of lateral branches can be induced. Thus, the growth of dormant axillary buds and the fate of their meristems are major determinants of plant architecture and lifespan. In Arabidopsis Col-0, AM induces the development of lateral inflorescences; this gene regulatory network mainly involves key genes that regulate the vegetative-to-reproductive phase transition. In Arabidopsis Sy-0, however, AM-induced lateral growth remained vegetative, leading to an increase in the number of rosette leaves on stem nodes and the formation of aerial rosettes.
In summary, stem cells are the main source of plant longevity, and changes in plant longevity are highly dependent on stem cell activity and cell characteristics. Various developmental factors can be understood as stem cell-induced changes in plant longevity. This study discusses the role of stem cell activity or cellular identity in determining plant longevity, as well as the genetic mechanisms, hormonal signaling, and environmental factors that maintain stem cell fate in the long term. However, only a few genes have been found to be involved in the regulation of plant longevity, and the molecular mechanisms regulating plant longevity are still not well understood. How stem cell activity and cell fate affect changes in plant longevity is not very clear. Therefore, future studies are warranted to elucidate in detail the genetic and molecular mechanisms controlling stem cell homeostasis in the context of plant longevity variation.
Reference:
Karami, O.; et al. The imperial role of stem cells in determining plant longevity variation. Plant Communications. 2023, 100566. https://doi.org/10.1016/j.xplc.2023.100566
