Berger Yael, Harpaz-Saad Smadar, Brand Arnon, Melnik Hadas, Sirding Neti, Alvarez John Paul, Zinder Michael, Samach Alon, Eshed Yuval, Ori Naomi
The Robert H Smith Institute of Plant Sciences and Genetics in Agriculture and The Otto Warburg Minerva Center for Agricultural Biotechnology, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel.
Development. 2009 Mar;136(5):823-32. doi: 10.1242/dev.031625. Epub 2009 Jan 28.
Leaves are formed at the flanks of the shoot apical meristem (SAM) and develop into a variety of forms. In tomato, prolonged leaf patterning enables the elaboration of compound leaves by reiterative initiation of leaflets with lobed margins. In goblet (gob) loss-of-function mutants, primary leaflets are often fused, secondary leaflets and marginal serrations are absent, and SAMs often terminate precociously. We show that GOB encodes a NAC-domain transcription factor expressed in narrow stripes at the leaf margins, flanking the distal side of future leaflet primordia, and at the boundaries between the SAM and leaf primordia. Leaf-specific overexpression of the microRNA miR164, a negative regulator of GOB-like genes, also leads to loss of secondary-leaflet initiation and to smooth leaflet margins. Plants carrying a dominant gob allele with an intact ORF but disrupted miR164 binding site produce more cotyledons and floral organs, have split SAMs and, surprisingly, simpler leaves. Overexpression of a form of GOB with an altered miR164 binding site in leaf primordia leads to delayed leaflet maturation, frequent, improperly timed and spaced initiation events, and a simple mature leaflet form owing to secondary-leaflet fusion. miR164 also affects leaflet separation in Cardamine hirsuta, a Brassicaceae species with complex leaves. Genetic and molecular analyses suggest that GOB expression is intact in the simplified leaves of entire tomato mutants, which have a defect in a putative repressor of auxin responses. Our results show that GOB marks leaflet boundaries and that its accurate spatial, temporal and quantitative activity affects leaf elaboration in a context-dependent manner.
叶片在茎尖分生组织（SAM）的侧面形成，并发育成多种形态。在番茄中，长时间的叶片模式形成通过小叶边缘具裂片的反复起始，使复叶得以精细发育。在杯状（gob）功能缺失突变体中，初生小叶常融合，次生小叶和边缘锯齿缺失，且SAM常过早终止发育。我们发现，GOB编码一个NAC结构域转录因子，该因子在叶缘的狭窄条带、未来小叶原基远侧的侧翼以及SAM与叶原基之间的边界处表达。叶特异性过表达微小RNA miR164（一种GOB样基因的负调控因子）也会导致次生小叶起始丧失和小叶边缘平滑。携带显性gob等位基因（其开放阅读框完整但miR164结合位点被破坏）的植株产生更多子叶和花器官，具有分裂的SAM，且令人惊讶的是，叶片更简单。在叶原基中过表达一种miR164结合位点改变的GOB形式，会导致小叶成熟延迟、频繁出现起始时间和间隔不当的情况，以及由于次生小叶融合而形成的简单成熟小叶形态。miR164也影响碎米荠（一种具有复杂叶片的十字花科植物）的小叶分离。遗传和分子分析表明，在整个番茄突变体的简化叶片中，GOB表达是完整的，这些突变体在一个假定的生长素反应抑制因子中存在缺陷。我们的结果表明，GOB标记小叶边界，其精确的空间、时间和定量活性以上下文依赖方式影响叶片发育。
