Poplar Plants Overexpressing the Ubiquitin E3 Ligase PtrRZFP1 Display Enhanced Resistance Against Generalist Insects

Forest trees face numerous biotic challenges throughout their life cycle, including pathogens and leaf-chewing insects. Our previous research suggested that certain members of the RING ZINC FINGER PROTEIN (RZFP) family, particularly PtrRZFP1 in Populus trichocarpa, may play a role in insect-plant interactions. In this study, we found that the PtrRZFP1 gene is significantly upregulated by exogenous methyl jasmonate (MeJA), insect infestation, and mechanical injury. Specifically, overexpression of insectsin poplar plants enhances resistance against two major generalist insects, Mythimna separata and Spodoptera frugiperda. Conversely, suppressing this gene results in a reduced ability of the plants to fend off these insects. At the physiological level, our results indicated that PtrRZFP1 positively regulates leaf surface temperature and the rate of photosynthetic electron transport in poplar plants in response to insect attack. In addition, PtrRZFP1 can upregulate the content of hormones (including ABA, JA, and SA) and lignin in poplar leaves to cope with insects. Transcriptional analysis revealed that PtrRZFP1 activates pathways associated with lignin biosynthesis and JA signaling, thereby contributing to insect resistance. Investigations at the protein level also suggested that PtrRZFP1 may interact with proteins involved in biotic stress responses, mediating the complex dynamics of poplar-insect interactions. Overall, these findings underscore the multifaceted role of PtrRZFP1 in enhancing poplar resistance to generalist insects.