Poster: Organelle Biogenesis

Abs # 1167: The ER body, a novel ER-derived compartment, accumulating a b-glucosidase with an ER retention signal in Arabidopsis

Presenter:	Hara-Nishimura, Ikuko , ihnishi@gr.bot.kyoto-u.ac.jp
Authors	Hara-Nishimura, Ikuko  (A)   Matsushima, Ryo  (A)   Kondo, Maki  (B)   Nishimura, Mikio  (B)
Affiliations:	(A): Kyoto University (B): National Institute for Basic Biiology

The ER body is a novel compartment that is derived from endoplasmic reticulum (ER) in Arabidopsis. ER bodies were visualized in transgenic plants (GFP-h) expressing green fluorescent protein with an ER-retention signal, HDEL. In contrast to whole seedlings which have a wide distribution of the ER bodies, rosette leaves have no ER bodies. Recently we reported that wound stress induced the formation of many ER bodies in rosette leaves. ER bodies were also induced by treatment with methyl jasmonate, a plant hormone involved in the defense system of plants. The formation of ER bodies might be a novel and unique type of endomembrane system in the response of plant cells to environmental stresses. We isolated an Arabidopsis mutant nai1, in which fluorescent ER bodies were hardly detected in whole plants. We found that a 65-kDa protein was specifically accumulated in a 1000 g-pellet (P1) fraction of GFP-h plants, but not in the P1 fraction of nai1 plants. N-terminal peptide sequencing revealed that the 65-kDa protein was a b-glucosidase, PYK10, with an ER retention signal, KDEL. Immunocytochemistry showed that PYK10 was localized in the ER bodies. Compared with the accumulation of GFP-HDEL, which was associated with both cisternal ER and ER bodies, the accumulation of PYK10 was much more specific to ER bodies. PYK10 was one of the major proteins in cotyledons, hypocotyls and roots of Arabidopsis seedlings, while PYK10 was not detected in rosette leaves that have no ER bodies. These findings indicated that PYK10 is the main component of ER bodies. It is possible that PYK10 produces defense compounds when plants are damaged by insects or wounding. 1. Matsushima, R. et al. (2002) Plant Physiol., 130, 1807-1814. 2. Matsushima, R. et al. (2002) Plant J., in press.