Wang Linjie, Li Jifu, Liu Liting, Dong Rongshu, Liu Guodao, Rao Idupulapati M, Chen Zhijian
Key Laboratory of Crop Gene Resources and Germplasm Enhancement in Southern China, Ministry of Agriculture and Rual Affairs/Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou, 571101, China.
National Key Laboratory for Tropical Crop Breeding, Sanya, 572024, China.
Plant Physiol. 2025 Jan 6. doi: 10.1093/plphys/kiaf005.
Stylo (Stylosanthes guianensis) is a tropical legume that exhibits considerable tolerance to manganese (Mn) toxicity, which severely constrains plant growth in acidic soils. To elucidate the Mn detoxification mechanisms in stylo, this study investigated the excess Mn-regulated metabolic profile of stylo roots and examined the role of metabolic enzymes in Mn tolerance. Excess Mn triggered oxidative stress in the two stylo genotypes tested. However, Mn-stimulated activation of antioxidant defense systems was observed in the Mn-tolerant genotype RY5 but not in the Mn-sensitive genotype TF0317. Metabolomic analysis of the Mn-tolerant RY5 roots revealed numerous excess Mn-responsive metabolites, mainly related to flavonoids and phenolic acids. Furthermore, a set of genes involved in the phenylpropanoid/flavonoid pathway were upregulated by excess Mn in stylo roots, especially in RY5. We characterized the excess Mn-inducible gene SgPAL2, encoding phenylalanine ammonia-lyase. SgPAL2 localized to the endoplasmic reticulum. Compared to control plants, SgPAL2 overexpression led to increases in shoot and root dry weights under Mn-excess conditions, whereas SgPAL2 suppression had the opposite effect. Moreover, SgPAL2 overexpression dramatically altered secondary metabolism, particularly flavonoid metabolism. In a bioassay, the inhibition of root elongation caused by excess Mn was alleviated by treatment with exogenous calycosin, an SgPAL2-regulated isoflavonoid, suggesting calycosin can detoxify Mn. Taken together, these findings indicate that SgPAL2 plays a critical role in enhancing Mn tolerance in stylo through metabolic regulation.
柱花草（圭亚那柱花草）是一种热带豆科植物，对锰（Mn）毒性具有相当强的耐受性，而锰毒性在酸性土壤中会严重抑制植物生长。为了阐明柱花草中锰的解毒机制，本研究调查了过量锰调控的柱花草根系代谢谱，并研究了代谢酶在耐锰性中的作用。过量的锰在测试的两种柱花草基因型中引发了氧化应激。然而，在耐锰基因型RY5中观察到锰刺激抗氧化防御系统的激活，而在锰敏感基因型TF0317中未观察到。对耐锰的RY5根系进行代谢组学分析，发现了许多过量锰响应代谢物，主要与黄酮类化合物和酚酸有关。此外，柱花草根系中一组参与苯丙烷类/黄酮类途径的基因被过量的锰上调，尤其是在RY5中。我们对过量锰诱导的基因SgPAL2进行了表征，该基因编码苯丙氨酸解氨酶。SgPAL2定位于内质网。与对照植物相比，SgPAL过表达导致在锰过量条件下地上部和根部干重增加，而SgPAL2抑制则产生相反的效果。此外，SgPAL2过表达显著改变了次生代谢，特别是黄酮类代谢。在生物测定中，用外源毛蕊异黄酮（一种由SgPAL2调控的异黄酮）处理可缓解过量锰对根伸长的抑制，这表明毛蕊异黄酮可以解除锰毒。综上所述，这些发现表明SgPAL2通过代谢调控在增强柱花草的耐锰性中起关键作用。
