Plastidic G6PDH and root structure regulation are essential for high nitrogen use efficiency in highland barley adaptation to low nitrogen

Abstract

Nitrogen (N) use efficiency (NUE) is a major factor determining crop growth and productivity. It is closely related to N acquisition and assimilation efficiency. In this study, the respective responses and mechanisms of highland barley (Kunlun14) and barley (Ganpi6) were investigated under low N condition. The root length, plant height, root/shoot ratio, and relative root growth rate in Kunlun14 were greater than those in Ganpi6 under low N stress, suggesting Kunlun14 has stronger tolerance to low N. The contents of nitrate and amino acids were decreased more in Ganpi6 than in Kunlun14 under low N stress. Moreover, Kunlun14 maintained higher nitrate uptake, translocation and assimilation capacity than Ganpi6. Glucose-6-phosphate dehydrogenase (G6PDH) activity, especially the plastidic G6PDH (Pla-G6PDH) activity, was markedly induced by low N in Kunlun14. Glucosamine, a G6PDH inhibitor, reduced nitrate uptake and assimilation capacity under low N stress. qRT-PCR and RNA-Seq analysis showed that the expression of HvG6PDH3 , encoding Pla-G6PDH3, was markedly induced by low N in barley roots. In addition, the differentially expressed genes in barley roots involved in hormones, transcription factors and cell wall biosynthesis play key roles under low N by regulating root development and N metabolism. Overexpression of HvG6PDH3 in Arabidopsis up-regulated the expression of AtNRT1.5 and AtNRT2.1 and increased the nitrate uptake and translocation capacity, which resulted in higher seed yield in HvG6PDH3 -overexpressors under low N stress. Taken together, HvG6PDH3 and the genes involved in regulating root architecture play essential roles in Kunlun14 tolerance to low N, which is conductive to maintaining high N uptake and assimilation efficiency. • Highland barley (Kunlun14) has higher NUE than barley (Ganpi6) under low N stress. • HvG6PDH3 is involved in the tolerance of highland barley to low N by positively regulating N uptake and assimilation. • DEGs involved in plant hormones, transcription factors and cell wall biosynthesis play key roles under low N stress.