An endoplasmic reticulum-derived structure that is induced under stress conditions in Arabidopsis

The endoplasmic reticulum (ER) body is a characteristic structure derived from ER and is referred to as a proteinase-sorting system that assists the plant cell under various stress conditions. Fluorescent ER bodies were observed in transgenic plants of Arabidopsis expressing green fluorescent protein fused with an ER retention signal. ER bodies were widely distributed in the epidermal cells of whole seedlings. In contrast, rosette leaves had no ER bodies. We found that wound stress induced the formation of many ER bodies in rosette leaves. ER bodies were also induced by treatment with methyl jasmonate (MeJA), a plant hormone involved in the defense against wounding and chewing by insects. The induction of ER bodies was suppressed by ethylene. An electron microscopic analysis showed that typical ER bodies were induced in the non-transgenic rosette leaves treated with MeJA. An experiment using coi1 and etr1-4 mutant plants showed that the induction of ER bodies was strictly coupled with the signal transduction of MeJA and ethylene. These results suggested that the formation of ER bodies is a novel and unique type of endomembrane system in the response of plant cells to environmental stresses. It is possible that the biological function of ER bodies is related to defense systems in higher plants.