Morphophysiological and proteomic profiling unveiling mechanisms underlying nitrogen use efficiency in popcorn (Zea mays var. everta)

In this study we hypothesize that the contrasting nitrogen use efficiency (NUE) between popcorn (Zea mays var. everta) inbred lines P2 (high NUE) and L80 (low NUE) is driven by distinct morphophysiological responses and proteomic profiles found in leaves and roots. To elucidate the mechanisms involved, plants were cultivated in a greenhouse under high (100% N) and low (10% N) nitrogen conditions, in a randomized complete block design with two factorial treatment arrangements and seven blocks. Morphological and physiological traits such as photochemical and non-photochemical quenching, quantum yield of photosystem II, and potential photosynthesis were evaluated. Compared to L80, under low N, P2 exhibited 25.9% greater leaf area, 22.4% taller plants, 21.7% thicker stems and 113% higher shoot dry mass, as well as higher values of photochemical and non- photochemical quenching and quantum yield of photosystem II that drove to a maximum photosynthesis 16.5% higher than L80. Comparative proteomic analysis of the leaves identified 215 differentially accumulated proteins (DAPs) in P2 and 168 DAPs in L80, while in roots, 127 DAPs were observed in P2 and 172 in L80. Notably, in leaves, the response to oxidative stress, energy metabolism, and photosynthesis represented the main differences between P2 and L80. In roots, the nitrate transport, ammonium assimilation, and amino acid metabolism appear to have contributed to the improved NUE in P2. Consequently, this study provides valuable insights into the molecular mechanisms underlying NUE and opens avenues for molecular breeding aimed at selecting superior genotypes for the development of a more sustainable agriculture.