Datisca glomerata

Abstract: MODELS for the maintenance of androdioecy (the presence of male and hermaphrodite individuals in a breeding population) in plants predict that males must have a fertility at least double the male fertility of hermaphrodites in order to be maintained by selection1–3. An even greater advantage is required in partially self-fertilizing populations1–3 as the gain in fitness through increased pollen production is least when few ovules are available for outcrossing. Because such stringent theoretical requirements make the evolutionary stability of this breeding system highly unlikely, functional androdioecy is thought to be rare in plants, and indeed the only documented instance occurs in populations of Datisca glomerata (Datiscaceae)4. As such, these populations provide a unique opportunity to test predictions concerning the evolution of androdioecy in plants. Here we report high outcrossing rates (65–92%) in two androdioecious populations of D. glomerata using random amplified polymorphic DNA markers. These outcrossing rates, when analysed with respect to existing evidence concerning pollen production and inbreeding depression in this species, are sufficiently high to satisfy theoretical requirements for the maintenance of androdioecy.

Abstract: The ability to establish root nodule symbioses is restricted to four different plant orders. Soil actinobacteria of the genus Frankia can establish a symbiotic relationship with a diverse group of plants within eight different families from three different orders, the Cucurbitales, Fagales and Rosales. Phylogenetically, Frankia strains can be divided into four clusters, three of which (I, II, III) contain symbiotic strains. Members of Cluster II nodulate the broadest range of host plants with species from four families from two different orders, growing on six continents. Two Cluster II genomes were sequenced thus far, both from Asia. In this paper we present the first Frankia cluster II genome from North America (California), Dg2, which represents a metagenome of two major and one minor strains. A phylogenetic analysis of the core genomes of 16 Frankia strains shows that Cluster II the ancestral group in the genus, also ancestral to the non-symbiotic Cluster IV. Dg2 contains the canonical nod genes nodABC for the production of lipochitooligosaccharide Nod factors, but also two copies of the sulfotransferase gene nodH. In rhizobial systems, sulfation of Nod factors affects their host specificity and their stability. A comparison with the nod gene region of the previously sequenced Dg1 genome from a Cluster II strain from Pakistan shows that the common ancestor of both strains should have contained nodABC and nodH. Phylogenetically, Dg2 NodH proteins are sister to rhizobial NodH proteins. A glnA-based phylogenetic analysis of all Cluster II strains sampled thus far supports the hypothesis that Cluster II Frankia strains came to North America with Datisca glomerata following the Madrean-Tethyan pattern.

Abstract: Previous studies of the small angiosperm family Datiscaceae have drawn contradictory con- clusions regarding its monophyly. Clarification of the relationships among the family components is critical to the interpretation of breeding system evolution within this family. Datisca glomerata is the only androdioe- cious member of the otherwise dioecious family and an initial phylogenetic study suggested that this rare breeding system was derived from dioecy in this family. A subsequent, broader scope phylogenetic analysis of Datiscaceae and related families has since suggested that Datiscaceae are not monophyletic, calling into question earlier conclusions regarding the evolution of androdioecy in Datiscaceae. In the present study, the phylogenetic relationships of Datiscaceae and the sequence of breeding system evolution are reexamined. DNA sequences from three sources including nuclear 18S ribosomal DNA, the internal transcribed spacer (ITS) region of nuclear ribosomal DNA, and the chloroplast-encoded rbcL gene were analyzed phylogeneti- cally using parsimony. Results from analysis of rbcL, 18S, and a combined data set all agree that Datiscaceae do not form a monophyletic assemblage. Datisca appears as a sister group to Begoniaceae in all analyses, but the position of sister taxa Octomeles and Tetrameles relative to Datisca and other members of the Cucurbitales is unresolved. The two species of Datisca form separate monophyletic lineages according to ITS analysis, pro- viding no evidence for a progenitor-derivative relationship for the two species. Phylogenetic trees from analy- ses of rbcL and 18S disagree as to whether dioecy or monoecy is ancestral to Datisca, and thus provide no evi- dence as to which sexual system gave rise to androdioecy in D. glomerata, however, there is no evidence for