MAPK4 and infection: Within this pathway, genes, including LRR receptor-like serine/threonine-protein kinase (FLS2), mitogen-activated protein kinase kinase 4 (MKK4), mitogen-activated protein kinase 3 (MPK3), and WRKY transcription factor 22 (WRKY22), were significantly increased in grafted wax gourds (H, resistant) after the lapse of infection, whereas there were no obvious changes in the original wax gourds (T, susceptible) (Figure 6).