Nitrogen-Starved Wheat: A Multi-Omics Perspective From Epigenome Regulation to Grain Quality

Abstract

Nitrogen is the most yield-limiting macronutrient in wheat (Triticum aestivum L.), yet no prior review has integrated nitrogen deficiency symptomology, physiology, and multi-omics approaches encompassing transcriptomics, proteomics, metabolomics, and epigenomics into a single mechanistic framework for wheat specifically. Wheat's hexaploid genome, distinctive nitrogen remobilisation architecture, and unique grain protein composition generate responses that cannot be extrapolated from diploid cereals. Two stress modes must be distinguished: acute nitrogen withdrawal induces rapid NLP7-mediated NRT2 transporter activation within minutes, whereas chronic low-nitrogen supply drives sustained epigenetic and root architectural adaptations over weeks. Post-translational modifications, including NRT2 phosphorylation and thioredoxin-regulated starch biosynthetic enzyme activity, govern nitrogen remobilisation dynamics independently of transcript abundance. The novel synthesis offered here repositions epigenetic regulation, specifically H3K27ac and H3K27me3 dynamics at NRT2, GS, and storage protein loci, as a principal determinant of cultivar-specific nitrogen use efficiency operating independently of DNA sequence variation. Sub-genome homologue epigenetic asymmetry in hexaploid wheat provides phenotypic buffering capacity unavailable to diploid cereals. The rhizosphere microbiome is identified as an integral co-regulator of nitrogen acquisition whose molecular interactions with plant signalling networks remain uncharacterised. Three wheat-specific dimensions absent from rice and maize are identified: sub-genome epigenetic asymmetry, an unusually high nitrogen harvest index amplifying remobilisation failure costs, and a gliadin-glutenin quality trade-off driven by differential chromatin accessibility. Five knowledge gaps define the immediate research agenda: single-cell omics under nitrogen deficiency, developmental time-series multi-omics, CRISPR validation of NUE quantitative trait locus candidates, molecular characterisation of organic versus mineral nitrogen responses, and climate-nitrogen epigenomics under elevated carbon dioxide. Wheat-specific multi-omics investment is required as a primary research objective rather than an agronomic supplement.