Background and aims

Crop wild relatives, exposed to strong natural selection, exhibit effective tolerance traits against stresses. While an aggressive root proliferation phenotype has long been considered advantageous for a range of stresses, it appears to be counterproductive under drought due to its high metabolic cost. Recently, a parsimonious root phenotype, metabolically more efficient, has been suggested to be better adapted to semiarid environments, although it is not clear that this phenotype is a trait exhibited by crop wild relatives.

Methods

Firstly, we analysed the root phenotype and carbon metabolism in four Medicago crop wild relatives adapted to a semiarid environment and compared them with the cultivated M. truncatula Jemalong (A17). Secondly, we exposed the cultivated (probably the least adapted genotype to aridity) and the wild (the most common one in arid zones) M. truncatula genotypes to water deficit. The carbon metabolism response in different parts of their roots was analysed.

Results

A reduced carbon investment per unit of root length was a common trait in the four wild genotypes, indicative of an evolution towards a parsimonious root phenotype. During the water deficit experiment, the wild M. truncatula showed higher tolerance to drought, along with a superior ability of its taproot to partition sucrose and enhanced capacity of its fibrous roots to maintain sugar homeostasis.

Conclusion

A parsimonious root phenotype and the spatial specialization of root carbon metabolism represent two important drought tolerance traits. This work provides relevant findings to understand the response of Medicago species roots to water deficit.

中文翻译：

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释放大自然的抗旱能力：关注野生苜蓿种群的简约根表型和特化根代谢

 背景和目标

作物野生亲缘种，暴露于强大的自然选择，表现出对胁迫的有效耐受性状。虽然侵袭性的根系增殖表型长期以来一直被认为对一系列胁迫有利，但由于其高代谢成本，它在干旱下似乎适得其反。最近，一种吝啬的根表型，代谢效率更高，被认为更能适应半干旱环境，尽管目前尚不清楚这种表型是否是作物野生亲缘种所表现出的性状。

 方法

首先，我们分析了 4 种适应半干旱环境的 Medicago 作物野生近缘种的根系表型和碳代谢，并将其与栽培的 M. truncatula Jemalong （A17） 进行了比较。其次，我们将栽培的（可能是最不适应干旱的基因型）和野生（干旱地区最常见的一种）M. truncatula 基因型暴露于缺水的环境中。分析了它们根不同部分的碳代谢反应。

 结果

每单位根长的碳投资减少是四种野生基因型的共同特征，表明向简洁的根表型进化。在缺水实验中，野生 M. truncatula 表现出更高的耐旱性，同时其主根分配蔗糖的能力更强，其须根维持糖稳态的能力增强。

 结论

吝啬的根表型和根系碳代谢的空间特化代表了两个重要的耐旱性状。这项工作为了解苜蓿物种根对水分亏缺的响应提供了相关发现。