PIF4 enhances temperature-independent tolerance to TSWV in Nicotiana benthamiana.

Tomato spotted wilt virus (TSWV) significantly threatens agricultural productivity, causing significant production and yield losses. Higher temperature have been reported to further intensify the TSWV accumulation and disease severity in several crops. PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) has emerged as a key regulator of plant responses to multiple biotic and abiotic stresses; however, its precise role in plant immunity against TSWV has not been defined. To investigate this, we generated PIF4 knockout mutants and PIF4-overexpression lines of Nicotiana benthamiana by gene-editing and transgenic method, respectively. Loss of PIF4 function increased tolerance to TSWV in a temperature-dependent manner, characterized by delayed disease progression, significant upregulation of defense-related genes, robust ROS accumulation, and increased levels of salicylic acid. In contrast, TSWV infection was enhanced by PIF4 overexpression. These results demonstrate that PIF4 suppresses the plant defense mechanisms against TSWV, particularly under high temperatures. Our findings provide insights that may inform molecular breeding strategies aimed at improving crop tolerance to TSWV under variable temperature conditions.