Conserved Architecture, Divergent Function: Tomato Lunapark Proteins Remodel the Endoplasmic Reticulum Without Enhancing Pathogen Resistance

The endoplasmic reticulum (ER) is a dynamic membrane network that plays essential roles in protein secretion, lipid biosynthesis and cellular signalling. Its architecture is maintained by conserved ER-shaping proteins, including the recently identified Lunapark (LNP) family, which have primarily been characterised in Arabidopsis thaliana. Whether these mechanisms are conserved in crop species remains unknown. Here, we identify and characterise two tomato (Solanum lycopersicum) LNP proteins, SlyLNP1 and SlyLNP2, and investigate their roles in ER organisation and function. Both proteins localised to the ER but displayed distinct distribution patterns, with SlyLNP1 preferentially associated with cisternae and SlyLNP2 localising to both cisternae and tubules. Overexpression of either protein promoted cisternal expansion and altered ER network organisation. FRET-FLIM analyses demonstrated that both SlyLNP proteins interact with themselves, each other, the ER fusogen RHD3 and the membrane-curvature protein RTN1, indicating conservation of the ER-shaping machinery. Furthermore, SlyLNP overexpression reduced ER-to-Golgi trafficking, linking ER remodelling with secretory pathway function. In contrast to their Arabidopsis counterparts, however, expression of tomato LNP proteins in Nicotiana benthamiana did not reduce infection by Phytophthora infestans. Together, our findings demonstrate that the molecular mechanisms governing ER architecture are highly conserved in tomato while revealing that the physiological consequences of Lunapark-mediated ER remodelling have diverged between plant species.