LOCALIZATION OF BETA-GLUCURONIDASE IN PROTEIN BODIES OF TRANSGENIC TOBACCO SEED BY FUSION TO AN AMINO-TERMINAL SEQUENCE OF THE SOYBEAN LECTIN GENE

We examined the effect of the first 32 amino acids of the soybean seed lectin gene on subcellular localization of beta-glucuronidase (GUS) i n transgenic tobacco seeds. The coding region of a non-glycoslyated GU S protein served as a reporter gene inserted between two expression ca ssettes containing the 5' promoter and 3' non-coding regions of the le ctin gene. These expression cassettes were identical except for the pr esence or absence of the 32 amino acid N-terminal sequence that preced es the mature lectin protein. Tobacco leaf disks were transformed by A grobacterium tumefaciens and 13 independently transformed lines were t ested for genetic segregation ratios to define the number of independe ntly segregating insertion events. Both promoters resulted in developm ental and tissue specific expression of the GUS reporter gene. We dete rmined that when the GUS protein is preceded by the 32 amino acid N-te rminal lectin peptide, there is significant association of GUS activit y and protein with the protein bodies as determined by subcellular fra ctionation and by localization using immunogold electron microscopy. A lthough unexpected, these results indicate that the 32 amino acid N-te rminal sequence of the lectin protein which serves as a signal sequenc e is sufficient to send the attached protein to the protein bodies. Th ese expression cassettes with and without the 32 amino acid N-terminal sequence should be useful for expression of foreign proteins either i n the protein bodies or in the cytosol during seed development of soyb ean or other plants. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.