Antisense and sense expression of a sucrose binding protein homologue gene from soybean in transgenic tobacco affects plant growth and carbohydrate partitioning in leaves

We isolated a cDNA from a soybean library, which encodes sucrose binding protein (SBP) homologue, designated S-64. To analyze the function of the SEP homologue, transgenic tobacco plants were obtained by introducing chimeric genes containing the s-64 coding region linked to the 35S CaMV promoter, either in the sense or antisense orientation, via Agrobacterium tumefaciens-mediated transformation. The accumulation of the SEP homologue was increased in transgenic plants expressing the heterologous sbp gene, whereas those expressing the antisense construct had reduced levels of the protein. The antisense transgenic plants developed symptoms characteristic of an inhibition of sucrose translocation and displayed a reduction in plant growth and development. In contrast, overexpression of the protein accelerated plant growth and the onset of flowering induction. The overall developmental performance of the transgenic plants was correlated with their photosynthetic rate under normal conditions. While photosynthesis in the antisense lines was decreased, in the sense lines photosynthetic rates were increased. Furthermore, both antisense repression and overexpression of the SEP homologue in transgenic lines altered carbohydrate partitioning in mature leaves. Taken together, these results indicate that S-64 protein is functionally analogous to SEP, representing an important component of the sucrose translocation pathway in plants. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.