Transcriptome Analysis of Maize Ear Leaves under Long-Term Applications of Nitrogen Fertilizer and its Combinations with Phosphorus and Potassium Fertilizers

This study aims to investigate the utilization status of nitrogen (N), potassium (K) and phosphorus (P) fertilizers at molecular level in field conditions. Maize cultivar Luyu 16 was planted in 41-year-old plots treated with different fertilizer combinations: unfertilized (control), N fertilizer (N), N fertilizer with P (NP), N fertilizer with K (NK), and N fertilizer with P and K (NPK). The ear leaves at grain filling stage were harvested for transcriptome analysis using RNA-Seq techniques. Results showed that NPK enhanced the contents of chlorophyll, soluble sugar, and protein, and improved the activities of antioxidant enzymes but reduced malondialdehyde (MDA) content much, relative to other treatments. There were 1258, 4438, 5177, and 4505 differentially expressed genes (DEGs) identified from the paired comparisons of NvsCK, NKvsCK, NPvsCK and NPKvsCK, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that DEGs identified from different paired comparisons but involved in the same biological or metabolic process were having significant differences in numbers, transcript levels, and expression pattern. Many promising genes related to absorption, transport, and metabolism of N, P and K were identified. The combination of N together with K and/or P fertilizers induced more differential genes than sole N fertilizer application. This study would deepen our understanding of macronutrient utilization efficiency in crops.