Localization of an SLG protein expressed under the regulation of a tapetum-specific promoter in anthers of transgenic Brassica napus

Abstract

S-locus glycoprotein (SLG) is known to be one of the proteins related to self-incompatibility in Brassica, and its transcripts are detected in anthers as well as stigmas. However, an SLG protein has not been detected in anthers so far. Because of sporophytic control of the self-incompatibility (SI) phenotype of pollen, an SLG gene is expected to be expressed in the sporophytic tissue of anthers, i.e., the tapetum. Overexpression of an SLG gene in the tapetum would enable us to predict the localization and function of an SLG protein in anthers. In this study, an SLG gene of self-incompatible B. campestris under the control of a tapetum-specific promoter was introduced into self-compatible B. napus. Immunoblot analysis using anti-SLG antiserum detected the exogenous SLG protein in the immature anthers, but not in the mature anthers. Immunoelectron microscopy showed the SLG protein to be localized in the tapetum and in the exine cell wall layer at the stage when the tapetum was degenerating. This result indicates the possible movement of the SLG protein from the tapetum to the pollen surface. A pollination test indicated that the pollen of the transgenic B. napus did not gain the SI phenotype.