Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, CA 92521, USA.
Proc Natl Acad Sci U S A. 2012 Dec 18;109(51):21146-51. doi: 10.1073/pnas.1210789109. Epub 2012 Dec 4.
Leaves and flowers begin life as outgrowths from the edges of shoot apical meristems. Stem cell divisions in the meristem center replenish cells that are incorporated into organ primordia at the meristem periphery and leave the meristem. Organ boundaries, regions of limited growth that separate forming organs from the meristem, serve to isolate these two domains and are critical for coordination of organogenesis and meristem maintenance. Boundary formation and maintenance are poorly understood processes, despite the identification of a number of boundary-specific transcription factors. Here we provide genetic and biochemical evidence that the Arabidopsis thaliana transcription factor lateral organ boundaries (LOB) negatively regulates accumulation of the plant steroid hormone brassinosteroid (BR) in organ boundaries. We found that ectopic expression of LOB results in reduced BR responses. We identified BAS1, which encodes a BR-inactivating enzyme, as a direct target of LOB transcriptional activation. Loss-of-function lob mutants exhibit organ fusions, and this phenotype is suppressed by expression of BAS1 under the LOB promoter, indicating that BR hyperaccumulation contributes to the lob mutant phenotype. In addition, LOB expression is BR regulated; therefore, LOB and BR form a feedback loop to modulate local BR accumulation in organ boundaries to limit growth in the boundary domain.
叶片和花朵最初是从茎尖分生组织边缘的外生体发育而来。分生组织中心的干细胞分裂补充了被整合到分生组织边缘器官原基中的细胞，并离开分生组织。器官边界是限制生长的区域，将正在形成的器官与分生组织分开，对于协调器官发生和分生组织维持至关重要。尽管已经鉴定出许多边界特异性转录因子，但边界的形成和维持仍然是一个理解不深的过程。在这里，我们提供了遗传和生化证据，表明拟南芥转录因子侧生器官边界（LOB）负调控器官边界中植物甾体激素油菜素（BR）的积累。我们发现，LOB 的异位表达导致 BR 反应降低。我们鉴定出 BAS1，它编码一种 BR 失活酶，是 LOB 转录激活的直接靶标。LOB 功能丧失突变体表现出器官融合，而这种表型可以通过 BAS1 在 LOB 启动子下的表达来抑制，表明 BR 过度积累导致 lob 突变体表型。此外，LOB 表达受 BR 调控；因此，LOB 和 BR 形成一个反馈回路，以调节器官边界中局部 BR 积累，从而限制边界区域的生长。
