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

We isolated a cDNA from a soybean library, which encodes sucrose binding pr otein (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, ei ther in the sense or antisense orientation, via Agrobacterium tumefaciens-m ediated transformation. The accumulation of the SEP homologue was increased in transgenic plants expressing the heterologous sbp gene, whereas those e xpressing the antisense construct had reduced levels of the protein. The an tisense transgenic plants developed symptoms characteristic of an inhibitio n of sucrose translocation and displayed a reduction in plant growth and de velopment. In contrast, overexpression of the protein accelerated plant gro wth and the onset of flowering induction. The overall developmental perform ance of the transgenic plants was correlated with their photosynthetic rate under normal conditions. While photosynthesis in the antisense lines was d ecreased, in the sense lines photosynthetic rates were increased. Furthermo re, both antisense repression and overexpression of the SEP homologue in tr ansgenic lines altered carbohydrate partitioning in mature leaves. Taken to gether, these results indicate that S-64 protein is functionally analogous to SEP, representing an important component of the sucrose translocation pa thway in plants. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved .