Interestingly, the expression level of proteasome inhibitor subunit 1 (ZmPI31), a key gene that inhibits the maturation of the 20S proteasome to the 26S proteasome, was upregulated in single infection and co-infection, and the results of RT–qPCR were consistent with the transcriptome (Figure S3). This evidence concerns the gene PSMF1 and infection.