Data_Sheet_1_Genotypic Variation of Nitrogen Use Efficiency and Amino Acid Metabolism in Barley.zip

Owing to the large genetic diversity of barley and its resilience under harsh environments, this crop is of great value for agroecological transition and the need for reduction of nitrogen (N) fertilizers inputs. In the present work, we investigated the diversity of a North African barley genotype collection in terms of growth under limiting N (LN) or ample N (HN) supply and in terms of physiological traits including amino acid content in young seedlings. We identified a Moroccan variety, Laanaceur, accumulating five times more lysine in its leaves than the others under both N nutritional regimes. Physiological characterization of the barley collection showed the genetic diversity of barley adaptation strategies to LN and highlighted a genotype x environment interaction. In all genotypes, N limitation resulted in global biomass reduction, an increase in C concentration, and a higher resource allocation to the roots, indicating that this organ undergoes important adaptive metabolic activity. The most important diversity concerned leaf nitrogen use efficiency (LNUE), root nitrogen use efficiency (RNUE), root nitrogen uptake efficiency (RNUpE), and leaf nitrogen uptake efficiency (LNUpE). Using LNUE as a target trait reflecting barley capacity to deal with N limitation, this trait was positively correlated with plant nitrogen uptake efficiency (PNUpE) and RNUpE. Based on the LNUE trait, we determined three classes showing high, moderate, or low tolerance to N limitation. The transcriptomic approach showed that signaling, ionic transport, immunity, and stress response were the major functions affected by N supply. A candidate gene encoding the HvNRT2.10 transporter was commonly up-regulated under LN in the three barley genotypes investigated. Genes encoding key enzymes required for lysine biosynthesis in plants, dihydrodipicolinate synthase (DHPS) and the catabolic enzyme, the bifunctional Lys-ketoglutarate reductase/saccharopine dehydrogenase are up-regulated in Laanaceur and likely account for a hyperaccumulation of lysine in this genotype. Our work provides key physiological markers of North African barley response to low N availability in the early developmental stages.

鉴于大麦拥有丰富的遗传多样性且在恶劣环境中具备较强抗逆性，该作物对于农业生态转型以及降低氮肥（nitrogen, N）施用需求具有重要价值。本研究针对北非大麦基因型种质集合展开多样性分析，分别测定其在低氮（limiting N, LN）与高氮（ample N, HN）供应条件下的生长表现，以及幼苗期包含氨基酸含量在内的多项生理性状。我们鉴定出一个摩洛哥品种Laanaceur，在两种氮素营养条件下，其叶片中的赖氨酸积累量均为其他基因型的5倍。对该大麦种质集合的生理特性表征结果显示，大麦应对低氮胁迫的适应策略存在遗传多样性，并凸显了基因型×环境互作效应。在所有供试基因型中，氮素限制均会导致整体生物量下降、碳浓度升高，且更多光合产物被分配至根系，表明该器官发生了显著的适应性代谢活动。最为突出的多样性差异体现在叶片氮素利用效率（leaf nitrogen use efficiency, LNUE）、根系氮素利用效率（root nitrogen use efficiency, RNUE）、根系氮素吸收效率（root nitrogen uptake efficiency, RNUpE）以及叶片氮素吸收效率（leaf nitrogen uptake efficiency, LNUpE）这几项指标上。以LNUE作为反映大麦耐受低氮胁迫能力的目标性状，该指标与植株氮素吸收效率（plant nitrogen uptake efficiency, PNUpE）及RNUpE呈显著正相关。基于LNUE性状，我们将供试基因型划分为高、中、低三类低氮耐受等级。转录组学分析结果表明，信号传导、离子转运、免疫响应及胁迫响应是受氮素供应调控的主要功能通路。在供试的三个大麦基因型中，编码HvNRT2.10转运蛋白的候选基因在低氮条件下均呈现上调表达。在Laanaceur中，编码植物赖氨酸生物合成关键酶二氢吡啶二羧酸合酶（dihydrodipicolinate synthase, DHPS）的基因，以及编码分解代谢关键酶双功能赖氨酸-α-酮戊二酸还原酶/酵母氨酸脱氢酶（bifunctional Lys-ketoglutarate reductase/saccharopine dehydrogenase）的基因均发生上调，这大概率是该品种叶片赖氨酸超积累的分子机制。本研究明确了北非大麦在发育早期响应低氮胁迫的关键生理标志物。