Plant Chimaeras and Mosaics

Abstract

Plant chimaeras and mosaics are not only found in our gardens as variegated ornamentals. They also constitute valuable research tools with a range of applications in developmental and molecular biology. For example, much of our knowledge about the development of the shoot and root apical meristems is derived from studying patterns of variegation, and where patterns persist throughout the plant, deductions can be made as to the fate of individual meristematic cells and the number and arrangement of initial cells giving rise to a variety of plant organs or structures. At a molecular level, defined sectors can shed light on the cell autonomy of a certain trait, inform us about the propagation of molecular signals and indeed allow us to directly compare genetically distinct tissue sectors in an attempt to determine specific gene function.

Key Concepts:

  • Plant chimaeras comprise cells of distinct genomes, whereas in genetic mosaics, cells of different genotypes derived from the same zygote.

  • Cells with different genotypes or even from different species can communicate to form functional meristems and other tissues.

  • Continuous persistent sectors throughout a plant can be explained by a mosaic shoot apical meristem and can be used to create ‘developmental fate maps’.

  • The fate of most plant cells is determined late in development by their position rather than by their ancestry.

  • Sector boundary analysis is used to identify the number of cells set aside as progenitors of an organ.

  • Mosaic plants are used to analyse where a molecular signal originates and how it is propagated.

  • Sector analysis provides clues about the cell autonomy of a trait as well as specific gene function.

Keywords: chimaeras; genetic mosaics; shoot apical meristem; fate maps; cell lineage; sector analysis

Figure 1.

Variegated forms of (a) Hedera (ivy) and (b) Tradescantia (spiderwort).

Figure 2.

Schematic representation of shoot apical meristems comprising sectors and cell layers of different genetic make‐up and resulting leaf variegation (see text for explanations). (a) Sectorial chimaera (the three meristematic cell layers are indicated). (b) Periclinal chimaera. (c) Mericlinal chimaera.

Figure 3.

Sectored shoot and inflorescence of Arabidopsis thaliana as used by Bossinger and Smyth to study initiation patterns of flower and floral organ development (chlorophyll removed). Blue sectors are indicative of expression of the bacterial uidA reporter gene visualised by β‐glucuronidase (GUS) staining.

Figure 4.

Cross‐section (a) and schematic representation (b) of young poplar stem showing a genetically transformed tissue sector (blue staining) extending from the pith to the periderm. This sector can be interpreted as having derived from a single transformed initial. As it includes both xylem and phloem, it must have originated before the differentiation of these tissues from the procambium. Exclusion of pith and periderm from the sectored zone means that at the time of transformation, three distinct tissue layers existed in the developing shoot apical meristem. The stained sector occupies approximately 1/24th of the stem circumference, indicating that at the time of transformation and at this level of the developing apex some 24 procambial initials were arranged in a ring around a central pith surrounded by developing epidermal tissue (Spokevicius et al., ).

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Further Reading

Dawe RK and Freeling M (1991) Cell lineage and its consequences in higher plants. Plant Journal 1: 3–8.

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Irish VF and Sussex IM (1992) A fate map of the Arabidopsis embryonic shoot apical meristem. Development 115: 745–753.

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Langdale JA, Lane B, Freeling M and Nelson T (1989) Cell lineage analysis of maize bundle sheath and mesophyll cells. Developmental Biology 133: 128–139.

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Poethig RS (1989) Genetic mosaics and cell lineage analysis in plants. Trends in Genetics 5: 273–277.

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How to Cite close
Bossinger, Gerd, and Spokevicius, Antanas V(Feb 2011) Plant Chimaeras and Mosaics. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002090.pub2]