The role of the carboxypeptidase AMP1 in cell fate maintenance
Final Report Abstract
Plants can adjust their body plan to the environmental conditions of their growing location by the continuous formation of new organs. Post-embryonic organogenesis is sustained by the activity of stem cell niches called meristems. Meristems consist of different zones with distinct functions. Stem cells in the center produce daughter cells which are displaced to the periphery, where they undergo a gradual program of cell proliferation and subsequent differentiation to build up new organs and tissues. In the shoot meristem, this program includes the active suppression of stem cell identity in peripheral cells by the existing stem cells in the center. This mechanism ensures the maintenance of a single stem cell population and simultaneously provides a regenerative backup system in case the original stem cell population is lost. The molecular basis of this process is not resolved, and a better understanding of the factors involved might contribute to optimizing in vitro regeneration procedures that are crucial for innovative breeding approaches, such as genome editing. The putative carboxypeptidase AMP1 in Arabidopsis plays a central role in suppressing stem cell identity in the peripheral cells of the shoot meristem. However, the biochemical function of this enzyme is unidentified, and AMP1 activity could not be assigned to any of the known stem cell regulators. A role of AMP1 in the miRNA-dependent control of translation has been established in the past, however, how this activity is connected to its developmental functions is not resolved. Using a combination of genetic and molecularbiological approaches we examined the functional interaction between AMP1 and the HD-ZIP III transcription factors, miRNA-controlled determinants of shoot meristem specification. We could show that HD-ZIP III activity is enhanced in amp1 and significantly contributes to the stem cell defects of the mutant. Notably, tissue-specific misexpression of HD-ZIP III members in wild-type plants was fully sufficient to reestablish a pluripotent cell state in different tissues. Surprisingly, the limitation of HD-ZIP III expression by AMP1 occurs mainly at the transcriptional level rather than mediating miRNA- dependent inhibition of their translation. A miRNA-independent role of AMP1 in suppressing stem cell identity was further supported by local inhibition of miRNA function and genetic interaction studies with core components of the miRNA machinery. Taken together, we could show that HD-ZIP III proteins act as master regulators of pluripotency downstream of AMP1 and represent crucial targets to enhance regeneration. Finally, we could also characterize novel inhibitors of auxin transport that strongly enhance HD-ZIP III transcription and thus boost in vitro shoot formation in regeneration-recalcitrant species such as sunflower.
Publications
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Deciphering the role of the carboxypeptidase AMP1 in cell fate maintenance. Invited oral presentation at the International Symposium: “Secrets of stem cells underlying longevity and persistent growth in plants” April 26-28, 2021
Yang, S., Poretska, O. & Sieberer, T.
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A novel chemical inhibitor of polar auxin transport promotes shoot regeneration by local enhancement of HD‐ZIP III transcription. New Phytologist, 235(3), 1111-1128.
Yang, Saiqi; de Haan, Marjolein; Mayer, Julius; Janacek, Dorina P.; Hammes, Ulrich Z.; Poppenberger, Brigitte & Sieberer, Tobias
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Novel chemical strategies to boost shoot regeneration in recalcitrant crops. Oral presentation at the 4th International Conference on “Plant Cell & Tissue Culture in Vitro” July 4-5, 2022
Sieberer, T.
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ALTERED MERISTEM PROGRAM1 sustains cellular differentiation by limiting HD-ZIP III transcription factor gene expression. Plant Physiology, 196(1), 291-308.
Yang, Saiqi; Poretska, Olena; Poppenberger, Brigitte & Sieberer, Tobias
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AMP1, a key regulator of shoot development and stress tolerance, controls cell fate maintenance by limiting HD-ZIP III expression. Oral presentation at the 40th IPG Symposium “Plant Hormones at the Intersection of Stress and Development” May 21-25, 2024
Yang, S., Poretska, O., Poppenberger, B. & Sieberer, T.
