Capsella

Abstract: We provide a phylogenetic analysis of the genera Arabidopsis and Arabis based on nuclear ribosomal DNA sequences. We show that traditional taxonomical concepts within tribe Ara-bideae, which includes these genera, are highly artificial. Arabis and Arabidopsis are paraphyletic and consist of several different independent lineages. The genus Capsella, originally placed in tribe Lepideae, is related to North American Arabis and the Arabidopsis thaliana lineage. Other genera, including East Asian Yin-shania, North American Halimolobus, cosmopolitan Barbarea and Cardamine, and European Aubrieta are positioned among different Arabis lineages. One Arabis species, Arabis pauciflora, is only distantly related to tribe Arabideae. Base chromosome number reduction from n = 8 to n = 5 to 7 occurred several times, suggesting that lower base chromosome numbers than n = 8 are derived in tribe Arabideae. Current knowledge on the evolution and systematics of the genera Arabis and Arabidopsis and relationships within the mustard family are summarized and discussed in the light of convergent evolution and transfer of knowledge from Arabidopsis thaliana as a molecular model plant to other species of the Cruciferae.

Abstract: Several factors, singly or synergistically, may influence the behavior of weedy species under conditions of intraspecific competition. The species studied were Brownals inermis, B. tectorum, Capsella bursa-pastoris, Conysa canadensis, Plantago lanceolata, P. major, Se7tecio sylvaticuts, S. viscosus, and Silene acnglica. Some or all of the species were subjected to condi- tions of intraspecific competition involving variable regimes of: (1) seed-sowing density, (2) soil surface, (3) fertilizer, (4) moisture, and (5) habitat, i.e., greenhouse and non-greenlhouse (onditions. Initially the vegetative dry weight production per unit area increased as density in- creased for every species. After a certain density (relative to the species) was reached, produc- tion was independent of density. All species displayed considerable plasticity in that similar geno- types showed a great increase in seed production between high and low densities (e.g., over a 100-fold increase for Capsella bursa-pastoris). Mean seed weight was constant under variable con(litions of density, fertilizer, soil surface, and moisture in all species except Bromus tectorum. In nmixed stands, the population of each species is smaller than its potential maximum. The size of a population of seedlings may be determined by the number of microenvironments suitable for germination ("safe-sites") in an area. The populations of the respective species may bc further regulated by: (1) self-controlled germination (Bromus inlermis, ConyZa cana- densis, Plantago lanzceolata, and Silene anglica) ; (2) mortality (Plantago major); and (3) individual plasticity (Bromus tectorum, Capsella bursa-pastoris, Senecio sylvaticus, and S. viscosus).

Abstract: An activation tagging screen in which the cauliflower mosaic virus 35S enhancer was inserted randomly into an Arabidopsis genome homozygous for the floral homeotic mutation apetala2-1 (ap2-1) resulted in a line (28-5) with extraordinarily wide, heart-shaped ovaries. The ovary of the 28-5 ap2-1 mutant shows an oval shape because of increased numbers of enlarged cells. When the ap2-1 mutation is crossed out of the genetic background, more elongated rather than wider fruits are obtained. Normally, Arabidopsis fruits will develop to a normal size only when the ovules are present and fertilized. In the 28-5 single mutant, the siliques keep growing despite failure of fertilization and can reach nearly normal size. When wild-type pollen was used to pollinate the mutant pistil, the pollinated 28-5 silique became >10% longer and 40% wider than a wild-type silique, although producing very few seeds. The enhancer insertion in line 28-5 acts by hyperactivating a cytochrome P450 gene, CYP78A9. The pistil of 28-5 ap2-1 mutant flowers shows a structure similar to that of Capsella bursa-pastoris, a distant mustard relative of Arabidopsis, suggesting that the processes regulated by the CYP78A9-encoded protein may be involved in evolutionary control of carpel shape.