Regulatory mechanisms of ER body formation and its function in Brassicaceae plants

Endoplasmic reticulum (ER) bodies are unique ER subdomains with a spindle-shaped structure in Brassicaceae, Cleomaceae, and Capparaceae plants, and they accumulate high levels of β-glucosidases (BGLUs). ER body-localized BGLUs are crucial for the hydrolysis of glucosinolates that are responsible for the chemical defense. In Arabidopsis thaliana, ER body-deficient mutants are vulnerable to non-herbivorous arthropods and non-pathogenic fungi, and display altered root microbiota assembly. ER bodies are predominantly observed in seedlings and roots, as well as in the epidermal cells above leaf midveins and margins. Arabidopsis thaliana MERISTEM LAYER1 (ATML1) transcription factor controls ER body accumulation in leaves through the activation of the NAI1 transcription factor, which upregulates the expression of ER body-related genes. ER bodies are further induced by wounding, indicating that their accumulation is also controlled in response to environmental signals. Jasmonate plays a key role in regulating ER body induction through CORONATINE INSENSITIVE1 (COI1), and the transcription factors MYC2, MYC3, and MYC4, which further control the expression of MYB47 and MYB95, key regulators of ER body-related genes. The conservation of orthologous and paralogous genes among ER body-related genes is observed in Brassicaceae plant genomes, indicating the conservation of ER body accumulation mechanisms among Brassicaceae species.