The Pea Inner Nuclear Membrane SUN Domain Protein Modulates Plant (a)biotic Stress Responses by Regulating Nuclear Dynamics.

Plant inner nuclear membrane (INM) Sad1/UNC-84 (SUN) proteins are essential for maintaining nuclear morphology, positioning and gene expression during development and environmental stress conditions. Recent studies suggest their involvement in symbiosis and pathogen defence, but their precise role in plant immunity remains unclear. Given the importance of nuclear dynamics during plant-pathogen interactions, understanding the function of SUN proteins in immune signalling is essential. Here, we identify and characterise the pea (Pisum sativum) C-terminal SUN. Using knockdown (KD) and overexpression (OE) strategies in pea and/or Arabidopsis, we demonstrate that PsSUN localises to the INM and regulates pathogen-induced nuclear positioning, nuclear morphology and defence gene expression. PsSUN-KD increased nuclear circularity and sphericity, impaired nuclear relocation to the fungal penetration site, and inhibited powdery mildew growth. PsSUN-OE deformed the nuclear envelope (NE) and enhanced defence gene expression and pathogen resistance. PsSUN-OE also increased plant abiotic stress-responsive gene expression and abscisic acid sensitivity. Furthermore, we demonstrate that interactions between PsSUN and the Arabidopsis lamin-like protein KAKU4 likely influence both their localisation at the nuclear periphery and the architecture of the NE, with the extent of these effects depending on the expression levels of the two proteins. Our results suggest that SUN and nuclear lamina coordinately regulate plant NE architecture and stress responses.