Seed storage protein. (Microbial infection) Involved in tobacco mosaic virus (TMV) replication. Required for endoplasmic reticulum (ER) aggregations mediated by TMV main replicase (P126) upon viral infection. Predominantly expressed in the embryo and endosperm of developing seeds (PubMed:7827492, PubMed:19014699). Also present in seedlings (PubMed:19014699). First observed at 5 days post anthesis (DPA). Accumulates throughout subsequent stages of embryo development, in embryonic tissues such as cotyledons and embryo axis as well as in the endosperm. In young seedlings, strictly confined to the cotyledons, hypocotyl and root tip, 3-4 days after germination. Also detected in the trichomes of new leaves. (Microbial infection) Accumulates after 0.5 to 6 h of tobacco mosaic virus (TMV) infection. (Microbial infection) Reduced tobacco mosaic virus (TMV) accumulation associated with altered endoplasmic reticulum (ER) transition in TMV-infected cells. Belongs to the 7S seed storage protein family.