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Parasponia trees are the only non-legume species that form nitrogen-fixing root nodules with rhizobium. Based on its taxonomic position in relation to legumes ( Fabaceae), it is most likely that both lineages have gained this symbiotic capacity independently. Therefore, Parasponia forms a bridging species to understand the evolutionary constraints underlying this symbiosis. However, absence of key technologies to genetically modify Parasponia seriously impeded studies on these species. We employed Agrobacterium rhizogenes to create composite Parasponia andersonii plants that harbour transgenic roots. Here, we provide an optimized protocol to infect P. andersonii as well as its non-symbiotic sister species Trema tomentosa with A. rhizogenes. We show that the transformation efficiency is temperature dependent. Whereas the optimal growth temperature for both these species is 28 °C, the transformation is most efficient when co-cultivation with A. rhizogenes occurs at 21 °C. Using this optimized protocol up to 80 % transformation efficiency can be obtained. These robust transformation platforms will provide a strong tool to unravel the Parasponia-rhizobium symbiosis. [ABSTRACT FROM AUTHOR]

In the mutualistic symbioses between legumes and rhizobia, actinorhizal plants and Frankia, Parasponia sp. and rhizobia, and cycads and cyanobacteria, the N2-fixing microsymbionts exist in specialized structures (nodules or cyanobacterial zones) within the roots of their host plants. Despite the phylogenetic diversity among both the hosts and the microsymbionts of these symbioses, certain developmental and physiological imperatives must be met for successful mutualisms. In this review, phylogenetic and ecological aspects of the four symbioses are first addressed, and then the symbioses are contrasted and compared in regard to infection and symbio-organ development, supply of carbon to the microsymbionts, regulation of O2 flux to the microsymbionts, and transfer of fixed-N to the hosts. Although similarities exist in the genetics, development, and functioning of the symbioses, it is evident that there is great diversity in many aspects of these root-based N2-fixing symbioses. Each symbiosis can be admired for the elegant means by which the host plant and microsymbiont integrate to form the mutualistic relationships so important to the functioning of the biosphere. [ABSTRACT FROM AUTHOR]

In the mutualistic symbioses between legumes and rhizobia, actinorhizal plants andFrankia, Parasponiasp. and rhizobia, and cycads and cyanobacteria, the N2-fixing microsymbionts exist in specialized structures (nodules or cyanobacterial zones) within the roots of their host plants. Despite the phylogenetic diversity among both the hosts and the microsymbionts of these symbioses, certain developmental and physiological imperatives must be met for successful mutualisms. In this review, phylogenetic and ecological aspects of the four symbioses are first addressed, and then the symbioses are contrasted and compared in regard to infection and symbio-organ development, supply of carbon to the microsymbionts, regulation of O2 flux to the microsymbionts, and transfer of fixed-N to the hosts. Although similarities exist in the genetics, development, and functioning of the symbioses, it is evident that there is great diversity in many aspects of these root-based N2-fixing symbioses. Each symbiosis can be admired for the elegant means by which the host plant and microsymbiont integrate to form the mutualistic relationships so important to the functioning of the biosphere. [ABSTRACT FROM AUTHOR]

We used ITS and trnL sequence data, analyzed separately and combined by MP, to explore species relationships and concepts in Trema (Celtidaceae), a pantropical genus of pioneer trees. Whether Trema is monophyletic or includes Parasponia is still unresolved. Three clades within Trema received moderate to high support, one from the New World and two from the Old World, but their relationships were not resolved. In the New World, specimens of T. micrantha formed two groups consistent with endocarp morphology. Group I, with smaller brown endocarps, is a highly supported clade sister to T. lamarckiana. Group II, with larger black endocarps, is poorly resolved with several subclades, including the highly supported T. integerrima clade. Both Old World clades contain Asian and African species, with three or more species in each region. Trema orientalty is not monophyletic: specimens from Africa formed a highly supported clade sister to T. cifricana, while those from Asia were sister to T. aspera from Australia. [ABSTRACT FROM AUTHOR]

The pat gene, coding for phosphinothricin acetyltransferase (PAT) from Streptomyces viridochromogenes, was cloned behind the par promoter of the hemoglobin gene from Parasponia andersonii, Introduction into tobacco ( Nicotiana tabacum) resulted in predominantly root specific PAT expression. Application of 5 l/ha BASTA (herbicidal component: phosphinothricin) did not effect growth morphology and vigor of the plants. After application of 20 l/ha BASTA the plants showed herbicide damage. Nevertheless, they all recovered by forming new undamaged leaves and resumed full growth despite virtually non-detectable expression of the PAT enzyme in the leaves. [ABSTRACT FROM AUTHOR]

The first of two major steps in the infection process in roots of Parasponia rigida (Ulmaceae) following inoculation by Rhizobium strain RP501 involves the invasion of Rhizobium into the intercellular space system of the root cortex. The earliest sign of root nodule initiation is the presence of clumps of multicellular root hairs (MCRH), a response apparently unique among Rhizobium-root associations. At the same time or shortly after MCRH are first visible, cell divisions are initiated in the outer root cortex of the host plant, always subjacent to the MCRH. No infection threads were observed in root hairs or cortical cells in early stages. Rhizobial entry through the epidermis and into the root cortex was shown to occur via intercellular invasion at the bases of MCRH. The second major step in the infection process is the actual infection per se of host cells by the rhizobia and formation of typical intracellular infection threads with host cell accommodation. This infection step is probably the beginning of the truly symbiotic relationship in these nodules. Rhizobial invasion and infection are accompanied by host cortical cell divisions which result in a callus-like mass of cortical cells. In addition to infection thread formation in some of these host cortical cells, another type of rhizobial proliferation was observed in which large accumulations of rhizobia in intercellular spaces are associated with host cell wall distortion, deposition of electron-dense material in the walls, and occasional deleterious effects on host cell cytoplasm. [ABSTRACT FROM AUTHOR]