Shi Bihai, Zhang Cui, Tian Caihuan, Wang Jin, Wang Quan, Xu Tengfei, Xu Yan, Ohno Carolyn, Sablowski Robert, Heisler Marcus G, Theres Klaus, Wang Ying, Jiao Yuling
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.
PLoS Genet. 2016 Jul 11;12(7):e1006168. doi: 10.1371/journal.pgen.1006168. eCollection 2016 Jul.
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.
枝条分支需要建立含有干细胞的新分生组织；这一现象引发了关于分生组织命运精确调控的问题。在种子植物中，这些新分生组织在叶腋处起始，以实现侧枝分支。通过对叶腋细胞进行活细胞成像，我们发现腋生分生组织的起始需要一个持续表达分生组织标记基因无茎分生组织（STM）的分生细胞群体。STM表达的维持依赖于叶腋处最低水平的生长素。STM的异位表达不足以激活那些已经失去叶腋STM表达细胞的植物形成腋芽。这表明一些细胞经历了对发育命运的不可逆定向分化。在更成熟的叶片中，卷叶（REV）直接上调叶腋分生细胞中STM的表达，但在分化细胞中则不然，从而建立腋生分生组织。REV与STM区域的细胞类型特异性结合与表观遗传修饰相关。我们的数据支持腋生分生组织起始的阈值模型，即低水平的STM维持分生组织能力，而高水平的STM导致分生组织起始。
