The contribution of amino acids (AAs) to soil nitrogen (N) fluxes is higher than previously thought. The fact that AA uptake is pivotal for N nutrition in boreal ecosystems highlights plant AA transporters as key components of the N cycle. At the same time, very little is known about AA transport and respective transporters in trees. Tree genomes may contain thirteen or more genes encoding the LYSINE HISTIDINE TRANSPORTER (LHT) family proteins, and this complicates the study of their significance for tree N use efficiency. With the strategy of obtaining a tool to study N use efficiency, our aim was to identify and characterize a relevant AA transporter in hybrid aspen (Populus tremula L. x tremuloides Michx.). We identified PtrLHT1.2, the closest homolog of Arabidopsis thaliana AtLHT1, which is expressed in leaves, stems and roots. Complementation of a yeast AA uptake mutant verified the function of PtrLHT1.2 as an AA transporter. Furthermore, PtrLHT1.2 was able to fully complement the phenotypes of the Arabidopsis AA uptake mutant lht1 aap5, including early leaf senescence-like phenotype, reduced growth, decreased plant N levels and reduced root AA uptake. AA uptake studies finally showed that PtrLHT1.2 is a high affinity transporter for neutral and acidic AAs. Thus, we identified a functional AtLHT1 homolog in hybrid aspen, which harbors the potential to enhance overall plant N levels and hence increase biomass production. This finding provides a valuable tool for N nutrition studies in trees and opens new avenues to optimizing tree N use efficiency.

中文翻译：

---

有机氮营养：来自杂种白杨 (Populus tremula L. x tremuloides Michx) 的 LHT1.2 蛋白是一种功能性氨基酸转运蛋白，也是拟南芥 LHT1 的同源物

氨基酸 (AA) 对土壤氮 (N) 通量的贡献比以前认为的要高。AA 吸收对北方生态系统中 N 营养至关重要这一事实突出表明植物 AA 转运蛋白是 N 循环的关键组成部分。与此同时，人们对 AA 运输和树木中各自的转运蛋白知之甚少。树木基因组可能包含 13 个或更多编码赖氨酸组氨酸转运蛋白 (LHT) 家族蛋白的基因，这使得研究它们对树木氮利用效率的意义变得复杂。为了获得研究氮素利用效率的工具，我们的目标是鉴定和表征杂交白杨（Populus tremula L. x tremuloides Michx.）中的相关 AA 转运蛋白。我们确定了 PtrLHT1.2，最接近的同源物拟南芥AtLHT1，在叶、茎和根中表达。酵母 AA 摄取突变体的补充验证了 PtrLHT1.2 作为 AA 转运蛋白的功能。此外，PtrLHT1.2 能够完全补充拟南芥 AA 摄取突变体lht1 aap5的表型，包括早期叶片衰老样表型、生长减少、植物 N 水平降低和根 AA 吸收减少。AA 摄取研究最终表明 PtrLHT1.2 是中性和酸性 AA 的高亲和力转运蛋白。因此，我们在杂交白杨中鉴定了一个功能性 AtLHT1 同源物，它具有提高植物整体氮水平并因此增加生物量产量的潜力。这一发现为树木中的氮营养研究提供了一个有价值的工具，并为优化树木氮的利用效率开辟了新的途径。