The phytotoxin coronatine and the plant growth regulator methyl jasmonate (MeJA) inhibit the growth of Arabidopsis seedlings. Coronatine and MeJA induced the accumulation of an approximately 29-kD protein in wild-type seedlings but not in seedlings of the coi1 mutant, which is insensitive to both compounds. The approximately 29-kD protein was recognized not only by antibodies raised against the partially purified polypeptide, but also by antibodies raised against vegetative storage proteins (VSPs) from soybean (29 kD) and poplar (32 kD). In the absence of added MeJA/coronatine, the VSP-like protein was highly expressed in flowers and siliques but not in seeds, seedlings, or mature leaves of wild-type Arabidopsis. By contrast, this protein could not be detected in coi1 seedlings treated with coronatine or MeJA, and it was found in very low levels in the male sterile flowers of coi1. A transcript corresponding to the gene of the Arabidopsis 27-kD VSP precursor shows the same pattern of expression as the VSP-like protein. Significantly, the VSP-like protein was not detected in green siliques or seeds obtained from coi1 flowers fertilized with wild-type pollen. We conclude that the VSP-like protein is normally expressed in maternal tissues, where it is regulated by COI1, but is not essential for the development of siliques.