Nutritropism is a positive tropism towards nutrients in plant roots. An NH4+ gradient is a nutritropic stimulus in rice (Oryza sativa L.). When rice roots are exposed to an NH4+ gradient generated around nutrient sources, root tips bend towards and coil around the sources. The molecular mechanisms are largely unknown. Here, we analysed the transcriptomes of the inside and outside of bending root tips exhibiting nutritropism to reveal nutritropic signal transduction. Tissues facing the nutrient sources (inside) and away (outside) were separately collected by laser microdissection. Principal component analysis revealed distinct transcriptome patterns between the two tissues. Annotations of 153 differentially expressed genes implied that auxin, gibberellin, and ethylene signalling were activated differentially between the sides of the root tips under nutritropism. Exogenous application of transport and/or biosynthesis inhibitors of these phytohormones largely inhibited the nutritropism. Thus, signalling and de novo biosynthesis of the three phytohormones is necessary for nutritropism. Expression patterns of IAA genes implied that auxins accumulated more in the inside tissues, meaning that ammonium stimulus is transduced to auxin signalling in nutritropism as same as gravity stimulus in gravitropism. SAUR and expansin genes, which are known to control cell wall modification and to promote cell elongation in shoot gravitropism, were highly expressed in the inside tissues rather than the outside tissues, and our transcriptome data are unexplainable for differential elongation in root nutritropism.

中文翻译：

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水稻根尖的转录组分析揭示了营养性背后的生长素、赤霉素和乙烯信号传导

向营养性是对植物根部营养物质的正向性。NH4+ 梯度是水稻 (Oryza sativa L.) 的营养刺激物。当水稻根部暴露于营养源周围产生的 NH4+ 梯度时，根尖会向营养源弯曲并盘绕在营养源周围。其分子机制很大程度上是未知的。在这里，我们分析了表现出营养性的弯曲根尖内部和外部的转录组，以揭示营养性信号转导。通过激光显微切割分别收集面向营养源（内部）和远离营养源（外部）的组织。主成分分析揭示了两种组织之间不同的转录组模式。153 个差异表达基因的注释表明，在营养向性作用下，生长素、赤霉素和乙烯信号在根尖两侧的激活存在差异。外源应用这些植物激素的运输和/或生物合成抑制剂很大程度上抑制了营养作用。因此，三种植物激素的信号传导和从头生物合成对于营养性是必要的。IAA基因的表达模式表明生长素在内部组织中积累更多，这意味着铵刺激在向营养性中被转导为生长素信号传导，与向地性中的重力刺激相同。SAUR 和扩张蛋白基因已知控制细胞壁修饰并促进芽向地性中的细胞伸长，它们在内部组织而不是外部组织中高度表达，并且我们的转录组数据无法解释根营养性伸长的差异。