Drought stress is the major limiting factor in agriculture. Wheat, which is the most widely grown crop in the world, is predominantly cultivated in drought‐prone rainfed environments. Since roots play a critical role in water uptake, root response to water limitations is an important component for enhancing wheat adaptation. In an effort to discover novel genetic sources for improving wheat adaptation, we characterized a wheat translocation line with a chromosomal segment from Agropyron elongatum , a wild relative of wheat, which unlike common wheat maintains root growth under limited‐water conditions. By exploring the root transcriptome data, we found that reduced transcript level of LATERAL ROOT DENSITY (LRD) gene under limited water in the Agropyron translocation line confers it the ability to maintain root growth. The Agropyron allele of LRD is down‐regulated in response to water limitation in contrast with the wheat LRD allele, which is up‐regulated by water deficit stress. Suppression of LRD expression in wheat RNAi plants confers the ability to maintain root growth under water limitation. We show that exogenous gibberellic acid (GA) promotes lateral root growth and present evidence for the role of GA in mediating the differential regulation of LRD between the common wheat and the Agropyron alleles under water stress. Suppression of LRD also had a positive pleiotropic effect on grain size and number under optimal growth conditions. Collectively, our findings suggest that LRD can be potentially useful for improving wheat response to water stress and altering yield components.

中文翻译：

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侧根密度基因在小麦水分胁迫期间调节根系生长。

干旱胁迫是农业的主要限制因素。小麦是世界上种植最广泛的作物，主要在干旱的雨养环境中种植。由于根在水分吸收中发挥着关键作用，根对水分限制的反应是增强小麦适应能力的重要组成部分。为了发现改善小麦适应性的新遗传来源，我们对小麦易位系进行了表征，该易位系具有来自小麦野生近缘种冰草（Agropyron elongatum）的染色体片段，与普通小麦不同，它能够在有限的水分条件下保持根部生长。通过探索根转录组数据，我们发现冰草易位系中，在有限的水分条件下，侧根密度（LRD）基因的转录水平降低，使其具有维持根生长的能力。LRD的 Agropyron 等位基因因水分限制而下调，而小麦LRD等位基因则因缺水胁迫而上调。抑制小麦 RNAi 植物中的LRD表达赋予其在水分限制下维持根系生长的能力。我们发现外源赤霉酸（GA）促进侧根生长，并为 GA 在介导水分胁迫下普通小麦和冰草等位基因之间LRD差异调节中的作用提供了证据。在最佳生长条件下， LRD的抑制对晶粒尺寸和数量也具有积极的多效性作用。总的来说，我们的研究结果表明LRD可能有助于改善小麦对水分胁迫的反应和改变产量组成。