Overexpression of GmHIR1 in Soybean Enhances Phytophthora sojae Resistance

Phytophthora root rot is a major disease that reduces soybean yield and quality. The role of hypersensitive-induced response (HIR) proteins in soybean resistance to Phytophthora sojae (P. sojae) remains unclear. In this study, wild-type W82, GmHIR1 overexpression lines (OE1 and OE2), and CRISPR/Cas9 knockout mutants (Q48 and Q54) were used to characterize GmHIR1 function. GmHIR1 was induced after P. sojae infection. The knockout mutants showed larger lesions, higher pathogen biomass and increased cell death at infection sites. In contrast, the overexpression lines exhibited reduced lesion size, lower pathogen accumulation, and weaker staining signals. These results indicate that GmHIR1 positively regulates soybean resistance to P. sojae. Further transcriptomic and proteomic analyses showed that GmHIR1 overexpression caused broad changes in infection-induced molecular responses. Differentially regulated genes and proteins were mainly associated with Ca²⁺ and MAPK signaling, oxidative stress response, peroxidase activity, and phenylpropanoid and flavonoid metabolism. In summary, GmHIR1 acts as a positive regulator of soybean resistance to P. sojae. It may enhance resistance through association with early immune responses, redox homeostasis, programmed cell death regulation, and defense-related metabolic processes. This study identifies GmHIR1 as a candidate gene for improving soybean resistance to Phytophthora root rot.