Wang Jia-Wei, Schwab Rebecca, Czech Benjamin, Mica Erica, Weigel Detlef
Department of Molecular Biology, Max Planck Institute for Developmental Biology, D-72076 Tübingen, Germany.
Plant Cell. 2008 May;20(5):1231-43. doi: 10.1105/tpc.108.058180. Epub 2008 May 20.
Leaves of flowering plants are produced from the shoot apical meristem at regular intervals, with the time that elapses between the formation of two successive leaf primordia defining the plastochron. We have identified two genetic axes affecting plastochron length in Arabidopsis thaliana. One involves microRNA156 (miR156), which targets a series of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes. In situ hybridization studies and misexpression experiments demonstrate that miR156 is a quantitative, rather than spatial, modulator of SPL expression in leaf primordia and that SPL activity nonautonomously inhibits initiation of new leaves at the shoot apical meristem. The second axis is exemplified by a redundantly acting pair of cytochrome P450 genes, CYP78A5/KLUH and CYP78A7, which are likely orthologs of PLASTOCHRON1 of rice (Oryza sativa). Inactivation of CYP78A5, which is expressed at the periphery of the shoot apical meristem, accelerates the leaf initiation rate, whereas cyp78a5 cyp78a7 double mutants often die as embryos with supernumerary cotyledon primordia. The effects of both miR156-targeted SPL genes and CYP78A5 on organ size are correlated with changes in plastochron length, suggesting a potential compensatory mechanism that links the rate at which leaves are produced to final leaf size.
开花植物的叶子由茎尖分生组织定期产生，两个连续叶原基形成之间所经过的时间定义了叶龄期。我们已经在拟南芥中鉴定出影响叶龄期长度的两个遗传轴。一个涉及微小RNA156（miR156），它靶向一系列类SQUAMOSA启动子结合蛋白（SPL）基因。原位杂交研究和异位表达实验表明，miR156是叶原基中SPL表达的定量调节剂，而非空间调节剂，并且SPL活性非自主地抑制茎尖分生组织中新叶的起始。第二个轴以一对具有冗余作用的细胞色素P450基因CYP78A5/KLUH和CYP78A7为例，它们可能是水稻（Oryza sativa）叶龄期1（PLASTOCHRON1）的直系同源基因。在茎尖分生组织周边表达的CYP78A5失活会加快叶片起始速率，而cyp78a5 cyp78a7双突变体通常作为具有多余子叶原基的胚胎死亡。miR156靶向的SPL基因和CYP78A5对器官大小的影响都与叶龄期长度的变化相关，这表明存在一种潜在的补偿机制，将叶片产生的速率与最终叶片大小联系起来。
