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.