Overexpression of EXO70E2 in Arabidopsis thaliana Disrupts Normal Development and Enhances Susceptibility to the Necrotrophic Fungus Botrytis cinerea.

Background: The exocyst complex, a conserved hetero-octameric complex including the EXO70 subunit, is a pivotal regulator of various cellular and developmental processes in plants. Among the diverse EXO70 isoforms, the specific function of EXO70E2-a primary organizer of exocyst-positive organelles (EXPOs)-remains to be fully elucidated. Methods: Here, we investigated the functional impact of constitutive EXO70E2 overexpression in Arabidopsis thaliana. Results: We observe that EXO70E2 overexpression leads to severe etiolation and dwarfism, accompanied by dose-dependent inhibition of primary root elongation. The YFP-labeled EXO70E2 localizes to distinct punctate structures. Histochemical analysis shows EXO70E2 expression in root tips and leaf vasculature, and its promoter activity is strongly induced by the salicylic acid analog INA and pathogen infection. Further function dissection demonstrates that EXO70E2-overexpressing plants exhibit enhanced susceptibility to the necrotrophic fungus Botrytis cinerea, manifested as larger lesions, accelerated host cell death, and increased fungal biomass. Conclusions: Our findings position EXO70E2 as a key negative regulator of plant development and defense outcomes, which may play a role in the balance between growth and immunity.