Effects of Nutrient Elements on Growth and Expression of Insect-Defense Response Genes in IZanthoxylum bungeanum/I Maxim

In China, Zanthoxylum bungeanum Maxim, known as “Huajiao,” has a pleasant, fragrant flavor and several therapeutic properties. The nutritional content of plants is necessary for their defense response to insects. In this study, we analyzed the effects of soil fertilization treatments such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and special compound fertilizer for pepper (HZ) on the different growth parameters and expression of insect-defense-response genes in Z. bungeanum. The results show that the height and weight of prickly ash significantly differed after the application of fertilizers with different concentrations. Additionally, seedlings that were treated with low concentrations of nutrient fertilizers (N1, P1, K1, Ca1, and HZ1) were significantly higher, and they were selected for transcriptome analysis. According to transcriptomic analysis, a total of 65,566 unigenes were discovered, among which 61,379 corresponded to annotated protein-coding genes and 4187 to transcripts of novel protein-coding genes. A total of 294 unigenes were detected as candidate genes for regulating the defense response to insects, including 204 protease inhibitors, 29 plant lectins, and 61 other defense response genes. Additionally, trypsin inhibitors, cystatin, phytepsin, metalloproteinase, MMP, caffeic acid, resveratrol, and thiol proteinase inhibitors, ACA, TDC, and 28 BES1 were enriched in Z. bungeanum. Specifically, the leaves of Z. bungeanum that were treated with Ca and HZ fertilizations were dominated by the protease inhibitors. In addition, the type of fertilizer significantly affects gene expression in plants. The functional annotations were predicted by the number of differentially expressed genes and classified by GO and KEGG ontology enrichment analysis. Moreover, according to the GO database, biological processes were the largest group and contained a high frequency of differentially expressed genes. According to KEGG pathway results, significantly enriched genes belonged to the biosynthesis of secondary metabolisms, amino acid metabolism, and folding, sorting, and degradation. Overall, it was found that the type of fertilizer with low concentrations had an effect on Z. bungeanum’s primary and secondary metabolism, and these findings provided grounds for further research in forest protection science.