CsAP2L transcription factor regulates resistance of citrus fruit to Penicillium digitatum through lignin biosynthesis and ROS metabolism pathways

Green mold, caused by Penicillium digitatum (P. digitatum), is a major cause of post-harvest economic losses in citrus fruit. AP2 transcription factors are associated with growth stress in plants, however, their role in non-model crops like citrus fruit has been little studied. Therefore, this study aims to investigate the function of CsAP2L, which has been discovered and found in the nucleus. We find that CsAP2L can enhance resistance to green mold by using Agrobacterium-mediated transient overexpression in citrus fruit. Meanwhile, it is shown by RT-qPCR, electrophoretic mobility shift assay (EMSA), yeast one hybrid (Y1H) and dual luciferase reporter (DLR) experiments show that CsAP2L can activate the expression of disease resistance genes (CsCOMT1L, CsPOD and CsSOD4A) and repress the transcription of Cs4CL9 and CsSOD4AP. Furthermore, CsAP2L not only can promote the accumulation of lignin content but also can keep ROS in balance. In summary, CsAP2L enhances fruit resistance by regulating disease resistance genes in lignin biosynthesis and ROS metabolism pathways. This study provides new insights into the mechanism of fruit disease resistance.