PNAS：焦雨铃研究组解析植物信号传导

干细胞分化形成组织和器官，但目前尚不了解干细胞是否对于器官的形态建成仍有调控作用。经典的手术实验表明：在高等植物茎尖，侧生器官叶片的被-腹轴(又称近-远轴)极性建成受到茎尖干细胞调控(Sussex, 1951, Nature 167:651-652)。这个极性信号分子被称为Sussex信号(如图灰色箭头)，但其化学本质和分子机理一直未能解析。

我国科学家之前的研究表明生长素运输对于叶片极性建成有调控作用(Ni et al., 1999, Cell Res. 9:27-35)。根据这一线索，中国科学院遗传与发育生物学研究所焦雨铃课题组在拟南芥和番茄中通过荧光成像发现叶片原基中存在生长素浓度差异，近轴面(即叶片靠近茎尖一侧)生长素浓度较低。

此外，叶片原基发生之后，立即出现从近轴面向茎尖干细胞方向的生长素运输(如图红色箭头)。该研究在番茄中建立了显微操作体系，对茎尖的生长素分布和运输进行干扰。番茄中的显微操作结果结合拟南芥中转基因和遗传学结果表明，叶片原基近轴面的低生长素浓度和叶片与茎尖的生长素运输都对叶片极性的建成至关重要。干扰生长素运输导致近轴面生长素浓度升高;提高近轴面的生长素浓度导致叶片呈现无极性的远轴面化。

进一步研究证明生长素下游转录因子MONOPTEROS介导生长素信号调控叶片极性建成。此研究对于经典的Sussex信号在分子水平给出了机理性的解释，并证明了生长素对于以叶片为代表的植物器官极性建成的作用。

该研究成果于12月16日在线发表于《美国国家科学院院刊》(PNAS)上。该项目得到了科技部、自然科学基金委、植物基因组学国家重点实验室与中科院的资助。焦雨铃课题组的博士研究生齐继艳和汪颖博士为该文章的共同第一作者。

原文标题：Auxin depletion from leaf primordia contributes to organ patterning

原文摘要：Stem cells are responsible for organogenesis, but it is largely unknown whether and how information from stem cells acts to direct organ patterning after organ primordia are formed. It has long been proposed that the stem cells at the plant shoot apex produce a signal, which promotes leaf adaxial-abaxial (dorsoventral) patterning. Here we show the existence of a transient low auxin zone in the adaxial domain of early leaf primordia. We also demonstrate that this adaxial low auxin domain contributes to leaf adaxial-abaxial patterning. The auxin signal is mediated by the auxin-responsive transcription factor MONOPTEROS (MP), whose constitutive activation in the adaxial domain promotes abaxial cell fate. Furthermore, we show that auxin flow from emerging leaf primordia to the shoot apical meristem establishes the low auxin zone, and that this auxin flow contributes to leaf polarity. Our results provide an explanation for the hypothetical meristem-derived leaf polarity signal. Opposite to the original proposal, instead of a signal derived from the meristem, we show that a signaling molecule is departing from the primordium to the meristem to promote robustness in leaf patterning.

作者：阳光森林