Comprehensive analysis of the MLP genes in Paulownia fortunei and functional characterization of PfMLP25 in response to pathogen invasion

Major latex-like proteins (MLPs) play crucial regulatory roles in mediating plant responses to both abiotic and biotic stressors. Although MLPs have been identified in diverse plants, the genome-wide characteristics of MLP-encoding genes and their roles in pathogen defense in Paulownia (Paulownia fortunei) remain largely unexplored. P. fortunei is a fast-growing perennial tree widely cultivated across multiple regions of Asia due to its substantial economic and ecological value. Here, we identified 49 PfMLP genes from the P. fortunei genome and systematically characterized their sequence architectures and phylogenetic relationships. Transcriptome analyses revealed 16 PfMLPs that are responsive to Witches' Broom (PaWB) phytoplasma infection. Notably, we focused on the functional characterization of PfMLP25, whose expression was induced by PaWB infection. Heterogenous overexpression of PfMLP25 in transgenic poplars enhanced pathogen resistance, confirming its critical role in anti-pathogen defense. Additionally, we demonstrated that the PfMYB100 transcription factor regulates the transcription of PfMLP25 and identified its interaction with two key immune system-essential proteins, PfCDPKa and PfRODa. Furthermore, we validated the interaction between PfMLP25 and the PfPUBa protein, indicating a potential role for PfMLP25 in the ubiquitination pathway during PaWB phytoplasma invasion. Taken together, our findings suggest that PfMLP25 functions by mediating immune system activation and participating in ubiquitination processes during PaWB phytoplasma invasion. This study presents new insights into the role of PfMLP25 and its underlying molecular mechanisms in plant pathogen defense.