Bihai Shi , Cui Zhang , Caihuan Tian , Jin Wang , Quan Wang , Tengfei Xu ,Yan Xu , Carolyn Ohno , Robert Sablowski , Marcus G. Heisler , Klaus Theres ,Ying Wang , Yuling Jiao Two-Step Regulation of a Meristematic Cell Population Acting in Shoot Branching

Two-Step Regulation of a Meristematic CellPopulation Acting in Shoot Branching in Arabidopsis

Bihai Shi , Cui Zhang , Caihuan Tian , Jin Wang , Quan Wang , Tengfei Xu ,Yan Xu , Carolyn Ohno , Robert Sablowski , Marcus G. Heisler , Klaus Theres ,Ying Wang , Yuling Jiao

PLoS Genet 

DOI:10.1371/journal.pgen.1006168

Abstract:  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 MERIS-TEMLESS (STM). The maintenance of STM expression depends on the leaf axil auxin mini-mum. 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.