BACKGROUND Short internodes contribute to plant dwarfism, which is exceedingly beneficial for crop production. However, the underlying mechanisms of internode elongation are complicated and have been not fully understood. RESULTS Here, we report a maize dwarf mutant, dwarf2014 (d2014), which displays shortened lower internodes. Map-based cloning revealed that the d2014 gene is a novel br2 allele with a splicing variation, resulting in a higher expression of BR2-T02 instead of normal BR2-T01. Then, we found that the internode elongation in d2014/br2 exhibited a pattern of inhibition-normality-inhibition (transient for the ear-internode), correspondingly, at the 6-leaf, 12-leaf and 14-leaf stages. Indeed, BR2 encodes a P-glycoprotein1 (PGP1) protein that functions in auxin efflux, and our in situ hybridization assay showed that BR2 was mainly expressed in vascular bundles of the node and internode. Furthermore, significantly higher auxin concentration was detected in the stem apex of d2014 at the 6-leaf stage and strictly in the node region for the ear-internode at the 14-leaf stage. In such context, we propose that BR2/PGP1 transports auxin from node to internode through the vascular bundles, and excessive auxin accumulation in the node (immediately next to the intercalary meristem) region suppresses internode elongation of d2014. CONCLUSIONS These findings suggest that low auxin levels mediated by BR2/PGP1 in the intercalary meristem region are crucial for internode elongation.

中文翻译：

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玉米brachytic2（br2）抑制下节间的伸长，而在节间分生组织区域中过长的植物生长素积聚。

背景技术节间短促成植物矮化，这对作物生产极为有利。但是，节间伸长的基本机制很复杂，尚未完全了解。结果在这里，我们报道了一个玉米矮化突变体dwarf2014（d2014），该突变体的下部节间缩短。基于图谱的克隆显示，d2014基因是具有剪接变异的新型br2等位基因，导致BR2-T02的表达高于正常BR2-T01。然后，我们发现d2014 / br2中的节间伸长在6叶片，12叶片和14叶片阶段分别表现出抑制-正常-抑制（耳朵-节点间的瞬态）模式。实际上，BR2编码一种P-糖蛋白1（PGP1）蛋白，该蛋白在生长素外排中起作用，我们的原位杂交实验表明，BR2主要在节间和节间的血管束中表达。此外，在6叶期的d2014茎尖中以及在14叶阶段的耳节间的节点区域中严格检测到高的植物生长素浓度。在这种情况下，我们建议BR2 / PGP1通过血管束将生长素从节点运至节点间，而在节点（紧邻分生组织的中间）区域中过量的生长素蓄积会抑制d2014的节点间伸长。结论这些发现表明，由BR2 / PGP1介导的间生膜区域内的生长素水平低对于节间延长至关重要。在6叶期的d2014茎尖中和在14叶期的耳间节的节点区域中严格检测到了较高的生长素浓度。在这种情况下，我们建议BR2 / PGP1通过血管束将生长素从节点运到节点间，而在节点（紧邻cal间分生组织）区域内生长素的过多积蓄抑制了节点间伸长d2014。结论这些发现表明，由BR2 / PGP1介导的间生膜区域内的生长素水平低对于节间延长至关重要。在6叶期的d2014茎尖中和在14叶期的耳间节的节区中严格检测到明显较高的生长素浓度。在这种情况下，我们建议BR2 / PGP1通过血管束将生长素从节点运至节点间，而在节点（紧邻分生组织的中间）区域中过量的生长素蓄积会抑制d2014的节点间伸长。结论这些发现表明，由BR2 / PGP1介导的间生膜区域内的生长素水平低对于节间延长至关重要。节点中（紧邻分生组织的部位）区域中生长素的过度积聚会抑制d2014的节点间伸长。结论这些发现表明，由BR2 / PGP1介导的间生膜区域内的生长素水平低对于节间延长至关重要。节点中（紧邻分生组织的部位）区域中生长素的过度积聚会抑制d2014的节点间伸长。结论这些发现表明，由BR2 / PGP1介导的间生膜区域内的生长素水平低对于节间延长至关重要。