EXPRESSION OF SOYBEAN NODULIN-26 IN TRANSGENIC TOBACCO - TARGETING TOTHE VACUOLAR MEMBRANE AND EFFECTS ON FLORAL AND SEED DEVELOPMENT

Nodulin 26 is an integral membrane protein of the symbiosome membrane of nitrogen-fixing soybean nodules. We expressed a nodulin 26 cDNA in transgenic tobacco (TN26 tobacco) under the control of the cauliflower mosaic virus 35S promoter to study subcellular targeting and the phys iological effect(s) of its expression. Based on Northern and Western b lots, the expression of nodulin 26 mRNA and protein in transgenic plan ts is high in apical shoot sections, flowers, and stems, low in mature leaves, and absent in roots. Western blot analysis revealed high leve ls of transgenic nodulin 26 protein in tonoplast membranes. In contras t, nodulin 26 protein was not found in isolated plasma membranes, the soluble fraction, nor in chloroplast and mitochondria-enriched membran e fractions. About 50-60% of the flowers and pods from TN26 tobacco pl ants abscised prematurely. Seed capsule size and seed fill per capsule from the remainder of surviving flowers were about 50% of that of con trol plants. Pollen viability was found to be normal, but flowers from TN26 tobacco plants showed shorter anther filaments compared with con trol plants. Normal seed production and capsule size was restored by m anually crossing the stigmas from TN26 plants with isolated pollen fro m either transgenic or control plants. Thus, the aberrant filament gro wth could have resulted in the reproductive defects associated with th e plants.