Center of Plant, Soil Interaction and Natural Resources Biotechnology, Scientific and Technological Bioresource Nucleus (BIOREN), Universidad de La Frontera, Temuco, Chile.
Laboratorio de Fisiología y Genética Marina (FIGEMA), Centro de Estudios Avanzados de Zonas Áridas (CEAZA), Coquimbo, Chile; Facultad de Ciencias del Mar, Universidad Católica del Norte, Coquimbo, Chile.
Plant Physiol Biochem. 2021 Apr;161:191-199. doi: 10.1016/j.plaphy.2021.02.014. Epub 2021 Feb 16.
Embothrium coccineum produces cluster roots (CR) to acquire sparingly soluble phosphorus (P) from the soil through the exudation of organic compounds. However, the physiological mechanisms involved in carbon drainage through its roots, as well as the gene expression involved in the biosynthesis of carboxylates and P uptake, have not been explored. In this work, we evaluated the relationship between carboxylate exudation rate and phosphoenolpyruvate carboxylase (PEPC) activity in roots of E. coccineum seedlings grown in a nutrient-poor volcanic substrate. Second, we evaluated CR formation and the expression of genes involved in the production of carboxylates (PEPC) and P uptake (PHT1) in E. coccineum seedlings grown under three different P supplies in hydroponic conditions. Our results showed that the carboxylate exudation rate was higher in CR than in non-CR, which was consistent with the higher PEPC activity in CR. We found higher CR formation in seedlings grown at 5 μM of P supply, concomitant with a higher expression of EcPEPC and EcPHT1 in CR than in non-CR. Overall, mature CR of E. coccineum seedlings growing on volcanic substrates poor in nutrients modify their metabolism compared to non-CR, enhancing carboxylate biosynthesis and subsequent carboxylate exudation. Additionally, transcriptional responses of EcPEPC and EcPHT1 were induced simultaneously when E. coccineum seedlings were grown in P-limited conditions that favored CR formation. Our results showed, for the first time, changes at the molecular level in CR of a species of the Proteaceae family, demonstrating that these root structures are highly specialized in P mobilization and uptake.
穗花杉产生簇生根（CR），通过分泌有机化合物从土壤中获取难溶性磷（P）。然而，其根部通过碳排泄的生理机制，以及参与羧酸生物合成和 P 吸收的基因表达，尚未得到探索。在这项工作中，我们评估了在营养贫瘠的火山基质中生长的穗花杉幼苗的根中羧酸分泌率与磷酸烯醇丙酮酸羧化酶（PEPC）活性之间的关系。其次，我们评估了在水培条件下，在三种不同的 P 供应下，穗花杉幼苗中 CR 的形成以及参与羧酸（PEPC）和 P 吸收（PHT1）产生的基因的表达。我们的结果表明，CR 中的羧酸分泌率高于非 CR，这与 CR 中更高的 PEPC 活性一致。我们发现，在 5 μM P 供应下生长的幼苗中形成了更高的 CR，同时 CR 中的 EcPEPC 和 EcPHT1 的表达也高于非 CR。总的来说，在营养贫瘠的火山基质上生长的穗花杉幼苗的成熟 CR 与非 CR 相比，会改变其代谢，增强羧酸的生物合成和随后的羧酸分泌。此外，当穗花杉幼苗在有利于 CR 形成的 P 限制条件下生长时，EcPEPC 和 EcPHT1 的转录响应同时被诱导。我们的研究结果首次在 Proteaceae 科的一个物种的 CR 中显示了分子水平的变化，表明这些根结构在 P 动员和吸收方面高度特化。
