We have developed a high-throughput T-DNA insertional mutagenesis program in tomato using activation tagging to identify genes that regulate metabolic pathways. One of the activation-tagged insertion lines ( ant1 ) showed intense purple pigmentation from the very early stage of shoot formation in culture, reflecting activation of the biosynthetic pathway leading to anthocyanin accumulation. The purple coloration resulted from the overexpression of a gene that encodes a MYB transcription factor. Vegetative tissues of ant1 plants displayed intense purple color, and the fruit showed purple spotting on the epidermis and pericarp. The gene-to-trait relationship of ant1 was confirmed by the overexpression of ANT1 in transgenic tomato and in tobacco under the control of a constitutive promoter. Suppression subtractive hybridization and RNA hybridization analysis of the purple tomato plants indicated that the overexpression of ANT1 caused the upregulation of genes that encode proteins in both the early and later steps of anthocyanidin biosynthesis as well as genes involved in the glycosylation and transport of anthocyanins into the vacuole.

Methods for improving the efficiency of plant recovery from somatic embryos of cassava (Manihot esculenta Crantz) were investigated by optimizing the maturation regime and incorporating a desiccation stage prior to inducing germination. Somatic embryos were induced from young leaf lobes of in vitro grown shoots of cassava on Murashige and Skoog medium with 2,4-dichlorophenoxy acetic acid. After 15 to 20 days of culture on induction medium, the somatic embryos were transferred to a hormone free medium supplemented with activated charcoal. In another 18 days mature somatic embryos became distinctly bipolar and easily separable as individual units and were cultured on half MS medium for further development. Subsequent desiccation of bipolar somatic embryos resulted in 92% germination and 83% complete plant regeneration. The plants were characterized by synchronized development of shoot and root axes. Of the non-desiccated somatic embryos, only 10% germinated and 2% regenerated plants. Starting from leaf lobes, transplantable plantlets were derived from primary somatic embryos within 70 to 80 days.

Regeneration of indica rice varieties remains a limiting factor for researchers undertaking rice Iransformation experiments. As reported for japonica rice and other crops, partial desiccation of indica rice calli dramatically promotes organogenesis and leads to high regeneration ability. We are now able to obtain 66.5%, 61.1% and 73.7% of calli that regenerate plants for the indica varieties TN1, IR72 and IR64 whereas in non desiccated controls only 30.0%, 15.5% and 18.7% of calli regenerated, respectively. Plants obtained were phenotypically normal and 50% were highly fertile. Partial desiccation is a reliable and simple method for improving indica rice regeneration. It also shortens the time of in vitro culture.

The morphogenetic responses of seedling explants of mung bean (Vigna radiata L.Wilczek cv ML-5) were studied in vitro. Direct induction of shoots/plants was possible from shoot tip, cotyledon and cotyledonary node explants. Dedifferentiation of the explants viz; Shoot tip, cotyledons, cotyledonary node, primordial leaves and roots was obtained on basal medium supplemented with auxin and cytokinin. Shoot regeneration was limited to primary calli while rhizogenesis was of common occurrence in established calli. In addition to differences in hormonal requirements, the various explants showed preferential growth in different basal media.

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We have developed an efficient transformation system for red raspberry (Rubus ideaus L.) using Agrobacterium mediated gene transfer. Using this system we have successfully introduced a gene that encodes an enzyme, S-adenosylmethionine hydrolase (SAMase), in raspberry cultivars Meeker (MK), Chilliwack (CH) and Canby (CY). Leaf and petiole expiants were inoculated with disarmed Agrobacterium tumefaciens strain EHA 105 carrying either of two binary vectors, pAG1452 or pAG1552, encoding gene sequences for SAMase under the control of the wound and fruit specific tomato E4 promoter. Primary shoot regenerants on selection medium were chimeral containing both transformed and non-transformed cells. Non-chimeral transgenic clones were developed by iterative culture of petiole, node and leaf explants, on selection medium, from successive generations of shoots derived from the primary regenerants. Percent recovery of transformants was higher with the selection marker gene hygromycin phosphotransferase (hpt), than with neomycin phosphotransferase (nptII). Transformation frequencies of 49.6%, 0.9% and 8.1% were obtained in cultivars Meeker, Chilliwack and Canby respectively from petiole expiants using hygromycin selection. Genomic integration of transgenes was confirmed by Southern hybridization. Transgenic plants from a total of 218 independent transformation events (161 MK, 4 CH, 53 CY) have been successfully established in soil.

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