Study on development of a new transgenic tomato plant having self-incompatibility gene from wild species.

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The present study aims to develop a new technique of molecular breeding for production of transgenic tomato genotypes having self-incompatibility gene originated from wild species of tomato, and for genetical control of plant reproduction by means of Agrobacterium-mediated gene transfer method. Solanaceous plants including wild relatives of tomato possess a gemetophytic self-incompatibility regulated by a single locus with multiple alleles (S-gene). The S-gene encodes a ribonuclease (S-RNase) that specifically expresses in pistil tissues of plant. A lot of cDNA clones and genomic clones encoding S-RNase have been reported from solanaceous plant species, e.g., Nicotiana, Petunia and Lycopersicon. On the other hand, the cultivated tomato plants are self-compatible, and genetic mechanisms leading to it's self-compatibility are not known. From research results of the present study, it was shown that in genetic transformants of a tomato cultivar "Aki-Tama" obtained through Agrobacterium- infected leaf-disks, the introduced S-RNase gene was identified as a single copy in the genome by Southern hybridization, and expressed specifically in the style tissue, as shown by Northern blot a malysis. The expressin level of the introduced gene was, however, very low, when compared with the wild species. This suggests that promoter region (lkbp of 5'-upstream region from ORF of S-RNase) used for construction of the Ti-vector is sufficient for tissue-specific expression, but not enough for enhancement of gene expression level. From RNase-activity staining after SDS-PAGE of stylar proteins, almost no activity of S-RNase was detected in tomato cultivars, indicating that self-compatibility of tomato is due to a low level of S-RNase activity in the style.