Showing papers by "Richard A. Jorgensen published in 1993"

The Germinal Inheritance of Epigenetic Information in Plants

Abstract: Germinally transmissible variants that arise by the anomalous imposition of developmental information on the genome are not uncommon in plant genetics, although they are often ignored. Better understanding of such variants is believed to be important because they appear to reflect basic features of developmental control processes. This paper briefly reviews classical genetic studies of such variants in plants, then discusses recent work on the genetic behaviour of plant transgenes, the results of which parallel and extend the classical genetic studies of these phenomena. An attempt is made to explain the molecular basis of these phenomena in terms of modern hypotheses on the dynamic organization of chromatin.

The origin of land plants: a union of alga and fungus advanced by flavonoids?

Abstract: This paper addresses the hypothesis that land plants have a biphyletic origin as the product of an endocellular mutualism between a green alga and a tip-growing, fungus-like organism, culminating in the acquisition of part of the latter's genome by the host alga (Atsatt, P.R., 1988, Are vascular plants 'inside-out' lichens? Ecology 69, 17-23). According to this hypothesis, the tip-growing symbiont's capacity for invasive growth was exploited during the further evolution of the holobiont for the development of various specialized plant cell types, but especially those displaying tip growth. Here, noting the recent discovery of the dependence of pollen tube tip growth on flavonoids, this hypothesis is refined and extended by suggesting that a symbiotic relationship was advanced by the evolution of UV-protective flavonoids in the alga, followed by the evolution of a growth response by the tip-growing symbiont to the presence of those flavonoids, allowing the symbiont to continue to live with the alga in its new, high-light habitat. This growth response then evolved into a dependence on flavonoids in the context of an obligate, mutualistic relationship progressing toward endosymbiosis and incorporation of the endocytobiont's genetic capacity for cell polarization, tip growth and their control into the host alga's genome. Land plants and advanced charophycean algae (which are the closest green-algal relatives of land plants) are likely products of this process, while a primitive charophycean alga (lacking both tip growth and cell polarization) is proposed to have been the likely host for the endocytobiont. A series of tests of this hypothesis, based mainly on the identification and molecular phylogenetic analysis of appropriate genes, are proposed. Whether the endocytobiont could have been a relative of the earliest endomycorrhizal fungi is assessed.

Elicitation of Organized Pigmentation Patterns by a Chalcone Synthase Transgene

Abstract: The problems of determination and elaboration of developmental patterns are more accessible in the case of visible patterns such as anthocyanin pigmentation patterns. Anthocyanin pigments offer the added advantage that they are completely dispensible in plant growth and development, which means that manipulation of anthocyanin pigmentation patterns generally has no deleterious or pleiotropic effects on the plant. Furthermore, many anthocyanin genes are known to act cell autonomously, so patterns of expression can visualized on a cell by cell basis. Coen et al. (1988) have discussed the basic principles behind flower color patterns with emphasis on Antirrhinum majus. Here I will focus on flower color patterns in Petunia hybrida and explain how the use of transgenes to manipulate patterns provides a tool with the potential to improve our understanding of how patterns are determined and elaborated.