Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo, 113-8657 Japan.
Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8601 Japan.
Plant Cell Physiol. 2024 May 14;65(4):671-679. doi: 10.1093/pcp/pcae003.
Nutritropism is a positive tropism toward 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 toward and coil around the sources. The molecular mechanisms are largely unknown. Here, we analyzed 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 signaling 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, signaling and de novo biosynthesis of the three phytohormones are 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 signaling in nutritropism similar to 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.
向化性是植物根系朝向营养物质的一种正向向性。NH4+ 浓度梯度是水稻（Oryza sativa L.）的一种向营养物质的向化刺激。当水稻根系暴露在由营养源产生的 NH4+ 浓度梯度中时，根尖会朝向并缠绕在营养源周围。其分子机制在很大程度上尚不清楚。在这里，我们分析了表现出向化性的弯曲根尖内外的转录组，以揭示向化性信号转导。通过激光微切割分别收集面向营养源的组织（内部）和远离营养源的组织（外部）。主成分分析显示，这两个组织之间的转录组模式存在明显差异。153 个差异表达基因的注释表明，在向化性下，根尖两侧的生长素、赤霉素和乙烯信号转导被不同程度地激活。这些植物激素的运输和/或生物合成抑制剂的外源应用在很大程度上抑制了向化性。因此，这三种植物激素的信号转导和从头生物合成对于向化性是必要的。IAA 基因的表达模式表明，生长素在内侧组织中积累更多，这意味着在向化性中，铵刺激类似于向重力性中重力刺激一样被转导到生长素信号转导中。SAUR 和 expansin 基因，已知在地上部向重力性中控制细胞壁修饰和促进细胞伸长，在内部组织中高度表达，而不是在外部组织中表达，我们的转录组数据无法解释根向化性中不同的伸长。
