Nuclear Localization of NPR1 Is Required for Activation of <i>PR</i> Gene Expression

TLDR

Systemic acquired resistance in plants relies on upregulation of pathogenesis‑related genes, a process regulated by the NPR1 protein whose mutations impair PR induction and overexpression enhances resistance. The study aimed to determine how NPR1’s subcellular localization influences its role in SAR. NPR1 was tagged with GFP to track nuclear accumulation, and a glucocorticoid‑receptor fusion was employed to inducibly control its nuclear import. Nuclear localization of NPR1 is essential for activating PR genes, as demonstrated by the steroid‑inducible system.

Abstract

Systemic acquired resistance (SAR) is a broad-spectrum resistance in plants that involves the upregulation of a battery of pathogenesis-related (PR) genes. NPR1 is a key regulator in the signal transduction pathway that leads to SAR. Mutations in NPR1 result in a failure to induce PR genes in systemic tissues and a heightened susceptibility to pathogen infection, whereas overexpression of the NPR1 protein leads to increased induction of the PR genes and enhanced disease resistance. We analyzed the subcellular localization of NPR1 to gain insight into the mechanism by which this protein regulates SAR. An NPR1–green fluorescent protein fusion protein, which functions the same as the endogenous NPR1 protein, was shown to accumulate in the nucleus in response to activators of SAR. To control the nuclear transport of NPR1, we made a fusion of NPR1 with the glucocorticoid receptor hormone binding domain. Using this steroid-inducible system, we clearly demonstrate that nuclear localization of NPR1 is essential for its activity in inducing PR genes.