Impacts of Nitrogen Deficiency on Wheat (Triticum aestivum L.) Grain During the Medium Filling Stage: Transcriptomic and Metabolomic Comparisons

Abstract

Nitrogen (N) supplementation is essential to the yield and quality of bread wheat (Triticum aestivum L.). The impact of N-deficiency on wheat at the seedling stage has been previously reported, but the impact of distinct N regimes applied at the seedling stage with continuous application on filling and maturing wheat grains is lesser known, despite the filling stage being critical for final grain yield and flour quality. Here, we compared phenotype characteristics such as grain yield, grain protein and sugar quality, plant growth, leaf photosynthesis of wheat under N-deficient and N-sufficient conditions imposed prior to sowing (120 kg/hm2) and in the jointing stage (120 kg/hm2), and then evaluated the effects of this continued stress through RNA-seq and GC-MS metabolomics profiling of grain at the mid-filling stage. The results showed that except for an increase in grain size and weight, and in the content of total sugar, starch, and fiber in bran fraction and white flour, the other metrics were all decreased under N-deficiency conditions. A total of 761 differentially expressed genes (DEGs) and 77 differentially accumulated metabolites (DAMs) were identified. Under N-deficiency, 51 down-regulated DEGs were involved in the process of impeding chlorophyll synthesis, chloroplast development, light harvesting, and electron transfer functions of photosystem, which resulted in the SPAD and Pn value decreased by 32 and 15.2% compared with N-sufficiency, inhibited photosynthesis. Twenty-four DEGs implicated the inhibition of amino acids synthesis and protein transport, in agreement with a 17–42% reduction in ornithine, cysteine, aspartate, and tyrosine from metabolome, and an 18.6% reduction in grain protein content. However, 14 DEGs were implicated in promoting sugar accumulation in the cell wall and another six DEGs also enhanced cell wall synthesis, which significantly increased fiber content in the endosperm and likely contributed to increasing the thousands-grain weight (TGW). Moreover, RNA-seq profiling suggested that wheat grain can improve the capacity of DNA repair, iron uptake, disease and abiotic stress resistance, and oxidative stress scavenging through increasing the content levels of anthocyanin, flavonoid, GABA, galactose, and glucose under N-deficiency condition. This study identified candidate genes and metabolites related to low N adaption and tolerance that may provide new insights into a comprehensive understanding of the genotype-specific differences in performance under N-deficiency conditions.

Transcriptome Analysis Reveals Different Responsive Patterns to Nitrogen Deficiency in Two Wheat Near-Isogenic Lines Contrasting for Nitrogen Use Efficiency

“…Heerah et al [ 53 ] revealed that WRKY1 regulates the expression of various nitrogen-related genes, including NRT2.1 and AMT1.1 genes, in Arabidopsis. Wang et al [ 54 ] reported that the expression of TIFY10c was promoted under N deficiency in wheat. Similarly, overexpression of TabHLH1 enhances the expression of NRT2.2 and several genes involved in the antioxidant enzyme under low-N stress in wheat [ 55 ].…”

Dissection of Crop Metabolome Responses to Nitrogen, Phosphorus, Potassium, and Other Nutrient Deficiencies

“…A series of physiological and molecular mechanisms underlying crop adaptation to N deficiency have been demonstrated, such as coordinating carbon (C) and N metabolisms, regulating root architecture, modulating phytohormone signaling, enhancing N uptake and translocation, and accumulating stress tolerance-related compounds [ 8 , 20 , 21 , 22 , 23 , 24 ]. Since total N content and crop growth are affected by N limitation, metabolome analysis has been performed to identify N deficiency responsive metabolites and metabolic pathways, dissecting the adaptive mechanisms through regulation of metabolic profiles in many crops, such as rice ( Oryza sativa ), maize ( Zea mays ), wheat ( Triticum aestivum ), barley ( Hordeum vulgare ), soybean ( Glycine max ), tomato ( Solanum lycopersicum ), and rapeseed ( Brassica napus ) [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. A summary of metabolome analyses of crops responses to N deficiency is presented in Table 1 .…”

“… [ 36 ] Wheat ( Triticum aestivum ) Grains 25 days post anthesis GC–MS 77 Increasing ornithine, cysteine, aspartate, and tyrosine; promoting sugar accumulation. [ 31 ] Rapeseed ( Brassica napus ) Leaves 14 LC–ESI-MS/MS 175 Decreasing aspartic acid; increasing l -alanine. [ 32 ] Rapeseed ( Brassica napus ) Roots 14 LC–ESI-MS/MS 166 Increasing aspartic acid.…”

Ear metabolism and genotype-by-environment interaction in field-grown durum wheat: identification of novel traits for crop improvement

“…An efficient use of N fertilisation that meets sustainability is necessary since it is the nutrient that most affects crop production and quality, but it is costly and its excessive use can cause soil and water pollution (Vicente et al, 2019b;Wang et al, 2021). Then, it is important to identify those physiological and metabolic parameters affected by N with an impact on GY and GQ.…”

“…N metabolism is a key factor for plant growth, with a crucial impact on GY and GQ traits, such as protein content, dough quality, and processing characteristics (Zörb et al, 2018;Wang et al, 2021). It is relevant for the wheat research to understand the N assimilation and remobilisation taking place in the different green organs, especially during grain filling.…”