Abstract
As sessile organisms, plants are exposed to extreme variations in environmental conditions over the course of their lives. Since plants grow and initiate new organs continuously, they have to modulate the underlying developmental program accordingly to cope with this challenge. At the heart of this extraordinary developmental plasticity are pluripotent stem cells, which are maintained during the entire life-cycle of the plant and that are embedded within dynamic stem cell niches. While the complex regulatory principles of plant stem cell control under artificial constant growth conditions begin to emerge, virtually nothing is known about how this circuit adapts to variations in the environment. In addition to the local feedback system constituted by the homeodomain transcription factor WUSCHEL (WUS) and the CLAVATA signaling cascade in the center of the shoot apical meristem (SAM), the bZIP transcription factor PERIANTHIA (PAN) not only has a broader expression domain in SAM and flowers, but also carries out more diverse functions in meristem maintenance: pan mutants show alterations in environmental response, shoot meristem size, floral organ number, and exhibit severe defects in termination of floral stem cells in an environment dependent fashion. Genetic and genomic analyses indicate that PAN interacts with a plethora of developmental pathways including light, plant hormone, and meristem control systems, suggesting that PAN is as an important regulatory node in the network of plant stem cell control.
Highlights
In contrast to most animals, plants continue to form new organs throughout their lives
AND OUTLOOK Taken together, we have shown here by molecular phenotyping and genetics that PAN is connected to a plethora of diverse input pathways and may act as an integrator to buffer shoot meristem activity
The same holds true for the PAN output network, which we found to include components of the circadian clock and stress response as examples for modulating environmental interactions
Summary
In contrast to most animals, plants continue to form new organs throughout their lives This remarkable capacity is dependent on the continuous presence of undifferentiated and self-renewing stem cells over long periods of time. Most notably WUSCHEL (WUS) and SHOOTMERISTEMLESS (STM ) are required for the maintenance of the shoot meristem (Barton and Poethig, 1993; Laux et al, 1996; Long et al, 1996; Mayer et al, 1998). Their inactivation causes premature differentiation and the eventual exhaustion of the stem cell pool, leading to the termination of the shoot meristem. The CLAVATA (CLV ) genes, have an opposite effect on meristems and if defective, shoot meristems overproliferate and expand inappropriately (Clark et al, 1993, 1995; Kayes and Clark, 1998)
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