Phylogenetic relationships, character evolution and biogeography of southern African members of Zygophyllum (Zygophyllaceae) based on three plastid regions.

The plastid coding rbcL and non-coding trnLF regions of 53 of 55 southern African Zygophyllum species were sequenced and used to evaluate the phylogenetic relationships within the southern African representatives of the genus. Published sequences of the same gene regions of Australian, Asian and North African Zygophyllum species were included to assess the relationships of the species from these regions to the southern African species. The addition of Z. stapffii from Namibia, found to be conspecific with Z. orbiculatum from Angola, lead to a greatly resolved tree. The molecular results were largely congruent with a recent sectional classification of the southern African species and supported their subdivision into subgenera Agrophyllum and Zygophyllum. Reconstruction of the character evolution of capsule dehiscence, seed attachment and seed mucilage showed that these characters allowed a division of southern African species into the two subgenera but that this could not be applied to species occurring elsewhere. Other morphological characters were found to vary and unique character combinations, rather than unique characters, were found to be of systematic value in sectional delimitation. The study suggests that repeated radiations from the horn of Africa to southern Africa and Asia and back lead to the present distribution of the taxa in the subfamily Zygophylloideae. Although this study supports some of the recent taxonomic changes in the group, the unresolved relationships between the proposed genera Tetraena and Roepera and those retained as Zygophyllum species suggest that changes to the taxonomy may have been premature.

T-DNA organization in tumor cultures and transgenic plants of the monocotyledon Asparagus officinalis.

Asparagus officinalis was the first monocotyledonous plant from which hormone-independent and opine-producing crown gall tissue could be isolated. We confirm by DNA hybridization that tumor lines obtained after infection of this plant by Agrobacterium strains harboring wild-type nopaline and octopine tumor-inducing (Ti) plasmids are stably transformed and contain transferred DNA (T-DNA) segments identical to the T-DNA found in dicotyledonous plants. We have also infected Asparagus with a nononcogenic T-DNA vector that carries a chimeric aminoglycoside phosphotransferase [NOS-APH(3')II] gene and selected transformed tissues on kanamycin-containing medium. The transformed status of these tissues was then confirmed by DNA hybridization. From these calli we regenerated kanamycin-resistant shoots that were subsequently rooted. Thus we report the isolation of transgenic monocotyledonous plants engineered via the Agrobacterium vector system.

Efficient octopine Ti plasmid-derived vectors for Agrobacterium-mediated gene transfer to plants.

A two-component cloning system to transfer foreign DNA into plants was derived from the octopine Ti plasmid pTiB6S3. pGV2260 is a non-oncogenic Ti plasmid from which the T-region is deleted and substituted by pBR322. pGV831 is a streptomycin-resistant pBR325 derivative that contains a kanamycin resistance marker gene for plant cells and a site for cloning foreign genes between the 25-bp border sequences of the octopine T-region. Conjugative transfer of pGV831 derivatives to Agrobacterium and cointegration by homologous recombination between the pBR322 sequences present on pGV831 and pGV2260, can be obtained in a single step. Strains carrying the resulting cointegrated plasmids transfer and integrate T-DNA into the genome of tobacco protoplasts, and transformed tobacco calli are readily selected as resistant to kanamycin. Intact plants containing the entire DNA region between the T-DNA borders have been regenerated from such clones. In view of these properties we present pGV831 and its derivatives as vectors for efficient integration of foreign genes into plants.