The RPW8s (Resistance to Powdery Mildew 8) are atypical broad-spectrum resistance genes that provide resistance to the powdery mildew fungi. Powdery mildew of rubber tree is one of the serious fungal diseases that affect tree growth and latex production. However, the RPW8 homologs in rubber tree and their role of resistance to powdery mildew remain unclear. In this study, four RPW8 genes, HbRPW8-a, b, c, d, were identified in rubber tree, and phylogenetic analysis showed that HbRPW8-a was clustered with AtRPW8.1 and AtRPW8.2 of Arabidopsis. The HbRPW8-a protein was localized on the plasma membrane and its expression in rubber tree was significantly induced upon powdery mildew infection. Transient expression of HbRPW8-a in tobacco leaves induced plant immune responses, including the accumulation of reactive oxygen species and the deposition of callose in plant cells, which was similar to that induced by AtRPW8.2. Consistently, overexpression of HbRPW8-a in Arabidopsis thaliana enhanced plant resistance to Erysiphe cichoracearum UCSC1 and Pseudomonas syringae pv. tomato DC30000 (PstDC3000). Moreover, such HbRPW8-a mediated resistance to powdery mildew was in a salicylic acid (SA) dependent manner. Taken together, we demonstrated a new RPW8 member in rubber tree, HbRPW8-a, which could potentially contribute the resistance to powdery mildew.

Powdery mildew caused by Erysiphe quercicola is a serious threat to natural rubber (Hevea brasiliensis) production, but the molecular basis of host immunity against this pathogen remains poorly understood. Here, we identify EqBPIE1 (E. quercicola Broad-spectrum Plant Immunity Elicitor 1), a fungal effector expressed during the mid-to-late colonization stage, that localizes to the cytosol, chloroplasts, and nucleus of host cells. EqBPIE1 enhances chloroplast-derived reactive oxygen species production, promotes perinuclear chloroplast clustering and stromule (stroma-filled tubule) formation, and thereby facilitates the relay of immune signals to the nucleus. In the nucleus, EqBPIE1 interacts with the NLR protein HbRG1 (H. brasiliensis Resistance Gene 1) to trigger hypersensitive cell death. Silencing EqBPIE1 increased susceptibility of H. brasiliensis to E. quercicola, whereas heterologous expression and foliar application conferred broad-spectrum resistance against fungal, bacterial, and oomycete pathogens in multiple plant species. Our findings establish an effector-mediated chloroplast-to-nucleus immune signaling pathway and highlight EqBPIE1 as a promising molecular tool for engineering durable, broad-spectrum disease resistance across crops.