Abstract
BackgroundNitrogen (N) is a macronutrient that is essential for optimal plant growth and seed yield. Allotetraploid rapeseed (AnAnCnCn, 2n = 4x = 38) has a higher requirement for N fertilizers whereas exhibiting a lower N use efficiency (NUE) than cereal crops. N limitation adaptation (NLA) is pivotal for enhancing crop NUE and reducing N fertilizer use in yield production. Therefore, revealing the genetic and molecular mechanisms underlying NLA is urgent for the genetic improvement of NUE in rapeseed and other crop species with complex genomes.ResultsIn this study, we integrated physiologic, genomic and transcriptomic analyses to comprehensively characterize the adaptive strategies of oilseed rape to N limitation stresses. Under N limitations, we detected accumulated anthocyanin, reduced nitrate (NO3−) and total N concentrations, and enhanced glutamine synthetase activity in the N-starved rapeseed plants. High-throughput transcriptomics revealed that the pathways associated with N metabolism and carbon fixation were highly over-represented. The expression of the genes that were involved in efficient N uptake, translocation, remobilization and assimilation was significantly altered. Genome-wide identification and molecular characterization of the microR827-NLA1-NRT1.7 regulatory circuit indicated the crucial role of the ubiquitin-mediated post-translational pathway in the regulation of rapeseed NLA. Transcriptional analysis of the module genes revealed their significant functional divergence in response to N limitations between allotetraploid rapeseed and the model Arabidopsis. Association analysis in a rapeseed panel comprising 102 genotypes revealed that BnaC5.NLA1 expression was closely correlated with the rapeseed low-N tolerance.ConclusionsWe identified the physiologic and genome-wide transcriptional responses of oilseed rape to N limitation stresses, and characterized the global members of the BnamiR827-BnaNLA1s-BnaNRT1.7s regulatory circuit. The transcriptomics-assisted gene co-expression network analysis accelerates the rapid identification of central members within large gene families of plant species with complex genomes. These findings would enhance our comprehensive understanding of the physiologic responses, genomic adaptation and transcriptomic alterations of oilseed rape to N limitations and provide central gene resources for the genetic improvement of crop NLA and NUE.
Highlights
Nitrogen (N) is a macronutrient that is essential for optimal plant growth and seed yield
Under severe N limitation, the ratio of root NO3− concentration to shoot NO3− concentration was significantly smaller than 1.0 (Fig. 1d-f), which indicated that the limited N nutrient resources were dominantly allocated to the shoots, which was less affected by N starvation than the roots, to facilitate the photosynthesis
The activity analyses of the N-metabolism associated enzymes revealed that the Nitrate reductase (NR) activity that was markedly reduced in the shoots did not significantly change in the roots (Fig. 1g, h), whereas the activity of glutamine synthetase was clearly elevated under N limitation (Fig. 1i, j)
Summary
Nitrogen (N) is a macronutrient that is essential for optimal plant growth and seed yield. N limitation adaptation (NLA) is pivotal for enhancing crop NUE and reducing N fertilizer use in yield production. Immense quantities of N fertilizers are applied worldwide annually to maintain crop productivity. This practice requires excessive amounts of energy and poses a remarkable threat to the environment. N use efficiency (NUE) is defined as the total biomass or grain yield produced per unit of applied fertilizer N [2], and improving NUE is critical for the favorable development of sustainable agriculture and ecosystem. Enhancement of plant N limitation adaptation (NLA) has shown to be an effective strategy to maintain or increase crop yields with reduced application of N fertilizers [2]
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