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PLoS Genet. 2016 Jul 11;12(7):e1006168. doi: 10.1371/journal.pgen.1006168. eCollection 2016 Jul.

Two-Step Regulation of a Meristematic Cell Population Acting in Shoot Branching in Arabidopsis.

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State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, and National Center for Plant Gene Research, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
Department of Plant Breeding and Genetics, Max Planck Institute for Plant Breeding Research, Cologne, Germany.
Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen, China.
State Key Laboratory of Crop Stress Biology in Arid Areas, Ministry of Agriculture Key Laboratory of Horticultural Plant Biology and Germplasm Innovation in Northwest China, College of Horticulture, Northwest A&F University, Yangling, Shaanxi, China.
Developmental Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
Cell and Developmental Biology Department, John Innes Centre, Norwich Research Park, Norwich, United Kingdom.
Frontier Laboratory of Crop Design, Beijing, China.


Shoot branching requires the establishment of new meristems harboring stem cells; this phenomenon raises questions about the precise regulation of meristematic fate. In seed plants, these new meristems initiate in leaf axils to enable lateral shoot branching. Using live-cell imaging of leaf axil cells, we show that the initiation of axillary meristems requires a meristematic cell population continuously expressing the meristem marker SHOOT MERISTEMLESS (STM). The maintenance of STM expression depends on the leaf axil auxin minimum. Ectopic expression of STM is insufficient to activate axillary buds formation from plants that have lost leaf axil STM expressing cells. This suggests that some cells undergo irreversible commitment to a developmental fate. In more mature leaves, REVOLUTA (REV) directly up-regulates STM expression in leaf axil meristematic cells, but not in differentiated cells, to establish axillary meristems. Cell type-specific binding of REV to the STM region correlates with epigenetic modifications. Our data favor a threshold model for axillary meristem initiation, in which low levels of STM maintain meristematic competence and high levels of STM lead to meristem initiation.

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