OsPIL1 Differentially Modulates Rice Blast Resistance Through Integrating Light or Darkness During Magnaporthe oryzae Infection.

Light and darkness are critical environmental factors that regulate plant immune responses. OsPIL1, a phytochrome-interacting factor-like protein, has been implicated in rice immunity against Magnaporthe oryzae, although its underlying mechanism remains unclear. This study aimed to dissect how OsPIL1 integrates light or darkness to modulate rice immunity. OsPIL1-overexpressing (OsPIL1 OE), Ospil1 knockout (ΔOspil1) and wild-type (WT) rice plants were pre-treated with light or darkness before inoculation. Blast disease symptoms, transcriptional changes in defence-related genes, and phytohormone levels were analysed to elucidate OsPIL1-associated defence responses. Transcriptomic (RNA-seq), proteomic (IP-MS) and protein interaction (Co-IP) analyses were employed to identify OsPIL1-regulated genes and interacting proteins. We found that light and darkness had contrasting effects on OsPIL1 OE plants. Darkness pre-treatment enhanced resistance in OsPIL1 OE plants, whereas light pre-treatment severely compromised it, exacerbating disease symptoms. Crucially, the ΔOspil1 ko plants exhibited increased susceptibility compared to WT, a phenotype that was significantly more pronounced under light, confirming that OsPIL1 functions as a negative regulator of immunity in a light-dependent manner. These phenotypes were correlated with corresponding changes in fungal colonisation, defence gene transcription and phytohormone profiles. RNA-seq analysis revealed differential expression of genes related to signalling pathways (kinases, phosphatases, transcription factors/repressors and ubiquitin-related proteins) under light and darkness in OsPIL1 OE plants. IP‒MS identified the cell wall invertase OsINV3 as a candidate interacting partner of OsPIL1, an interaction was confirmed via Co-IP assays. The results of functional assays suggest that this interaction contributes to resistance, potentially by modulating sugar signalling. Collectively, these findings demonstrate that OsPIL1 is a key signalling hub that negatively regulates rice immunity in the presence of light, with partial resistance retained in darkness through OsINV3 interaction. This study reveals a crucial light-dependent immune regulatory mechanism and offers potential targets for improving disease resistance in rice through molecular breeding or agronomic intervention.