Mepiquat chloride increases the Cry1Ac protein content of Bt cotton under high temperature and drought stress by regulating carbon and amino acid metabolism

The effects of mepiquat chloride (DPC) on the Cry1Ac protein content in Bacillus thuringiensis (Bt) cotton boll shells under high temperature and drought stress were investigated to provide a theoretical reference for Bt cotton breeding and high-yield and-efficiency cotton cultivation. This study was conducted using Bt cotton cultivar'Sikang 3' during the 2020 and 2021 growing seasons at Yangzhou University Farm, Yangzhou, Jiangsu Province, China. Potted cotton plants were exposed to high temperature and drought stress, and sprayed with either 20 mg L -1 DPC or water (CK). Seven days after treatment, the Cry1Ac protein content, alpha-ketoglutarate content, pyruvic acid content, glutamate synthase activity, glutamic oxaloacetic transaminase activity, soluble protein content, and amino acid content were measured, and transcriptome sequencing was performed. DESeq was used for differential gene analysis. Under the DPC treatment, the Cry1Ac protein content increased by 4.7-11.9% compared to CK. The alpha-ketoglutarate content, pyruvic acid content, glutamate synthase activity, glutamic oxaloacetic transaminase activity, soluble protein content, and amino acid content all increased. Transcriptome analysis revealed 7,542 upregulated genes and 10,449 downregulated genes for DPC vs . CK. Gene ontology (GO) and Kyoto Encyclopedia of Gene and Genomes (KEGG) analyses showed that the differentially expressed genes were mainly involved in biological processes, such as carbon and amino acid metabolism. For example, genes encoding 6-phosphofructokinase, pyruvate kinase, glutamic pyruvate transaminase, pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase, glutamate synthase, 1-pyrroline-5-carboxylate dehydrogenase, glutamic oxaloacetic transaminase, amino-acid N-acetyltransferase, and acetylornithine deacetylase were all significantly upregulated. The DPC treatment increased pyruvate, alpha-ketoglutarate, and oxaloacetate by increasing the operational rate of the glycolytic pathway of the citric acid cycle. It also significantly upregulated the genes encoding glutamate synthase, pyrrolidine-5-carboxylic acid dehydrogenase, glutamate oxaloacetate transaminase, and N-acetylglutamate synthetase, while it downregulated the genes encoding glutamine synthetase. Therefore, the synthesis of aspartic acid, glutamic acid, pyruvate, and arginine increased after treatment with DPC, and the Cry1Ac protein content was increased by regulating carbon and amino acid metabolism.