Adaption of Roots to Nitrogen Deficiency Revealed by 3D Quantification and Proteomic Analysis

Abstract

Rapeseed (Brassica napus) is an important oil crop worldwide. However, severe inhibition of rapeseed production often occurs in the field due to nitrogen (N) deficiency. The root system is the main organ to acquire N for plant growth, but little is known about the mechanisms underlying rapeseed root adaptions to N deficiency. Here, dynamic changes in root architectural traits of N-deficient rapeseed plants were evaluated by 3D in situ quantification. Root proteome responses to N deficiency were analyzed by the tandem mass tag-based proteomics method, and related proteins were characterized further. Under N deficiency, rapeseed roots become longer, with denser cells in the meristematic zone and larger cells in the elongation zone of root tips, and also become softer with reduced solidity. A total of 171 and 755 differentially expressed proteins were identified in shortand long-term N-deficient roots, respectively. The abundance of proteins involved in cell wall organization or biogenesis was highly enhanced, but most identified peroxidases were reduced in the N-deficient roots. Notably, peroxidase activities also were decreased, which might promote root elongation while lowering the solidity of N-deficient roots. These results were consistent with the cell wall components measured in the N-deficient roots. Further functional analysis using transgenic Arabidopsis (Arabidopsis thaliana) plants demonstrated that the two root-related differentially expressed proteins contribute to the enhanced root growth under N deficiency conditions. These results provide insights into the global changes of rapeseed root responses to N deficiency and may facilitate the development of rapeseed cultivars with high N use efficiency through rootbased genetic improvements.

Comparative genome and transcriptome analysis unravels key factors of nitrogen use efficiency in Brassica napus L

“…It is well documented that plants can alter root architecture to enhance N acquisition under N deficiency conditions to adapt to N‐deficient environments (Kiba & Krapp, ; Qin et al, ; White et al, ). The hydroponic experiment showed that the root morphologies of the two B. napus genotypes were affected differently: D4‐15 had more root tips and larger root surface area than D2‐1 under N deficient conditions (Figure S1), suggesting that greater plasticity of the root system might contribute to enhanced NupE and NUE in B. napus (Qin et al, ).…”

“…It is well documented that plants can alter root architecture to enhance N acquisition under N deficiency conditions to adapt to N‐deficient environments (Kiba & Krapp, ; Qin et al, ; White et al, ). The hydroponic experiment showed that the root morphologies of the two B. napus genotypes were affected differently: D4‐15 had more root tips and larger root surface area than D2‐1 under N deficient conditions (Figure S1), suggesting that greater plasticity of the root system might contribute to enhanced NupE and NUE in B. napus (Qin et al, ). Besides changes in root architecture, which affects NupE and NutE, such as N assimilation, remobilization of plant N from senescent to newly growing tissues, and alteration of carbohydrate partitioning might also contribute to NUE (Han, Okamoto, Beatty, Rothstein, & Good, ; Tegeder & Masclaux‐Daubresse, ).…”

“…It is well documented that plants can alter root architecture to enhance N acquisition under N deficiency conditions to adapt to Ndeficient environments (Kiba & Krapp, 2016;Qin et al, 2019;. The hydroponic experiment showed that the root morphologies of the two B. napus genotypes were affected differently:…”

“…D4-15 had more root tips and larger root surface area than D2-1 under N deficient conditions ( Figure S1), suggesting that greater plasticity of the root system might contribute to enhanced NupE and NUE in B. napus (Qin et al, 2019). Besides changes in root architecture, which affects NupE and NutE, such as N assimilation, remobilization of plant N from senescent to newly growing tissues, and alteration of carbohydrate partitioning might also contribute to NUE (Han, Okamoto, Beatty, Rothstein, & Good, 2015;Tegeder & Masclaux-Daubresse, 2018).…”

“…In general, agronomic NUE can be split into two main characters (Moll, Kamprath, & Jackson, ), N acquisition efficiency (NupE) and N utilization efficiency (NutE) (White et al, ; Xu et al, ). N uptake capacity, which is determined by influx transporters located on the plasma membranes of root cells, is one of the major determinants of the NupE, in conjunction with an appropriate root architecture that responds to local and systemic N signals (O'Brien et al, ; Qin et al, ; White, George, Dupuy, et al, ). Following uptake by root cells, some nitrate is assimilated within the roots, whilst a larger proportion is translocated to the shoot, where it is first reduced to nitrite by nitrate reductase (NR) in the cytoplasm, then to ammonium by nitrite reductase (NiR) in the plastids, which is metabolized to glutamate (Glu) and glutamine (Gln) by Gln synthetase (GS) and Glu synthase (GOGAT), respectively (Tegeder & Masclaux‐Daubresse, ; Xu et al, ).…”