Extra-chromosomal mutability determined by a nuclear gene locus in arabidopsis

Abstract

Two recessive mutations isolated after ethyl methanesulfonate treatment produce variegation when homozygous with excellent penetrance and variable expressivity. The variegation involves different degrees of pigmentation and morphology of the leaves as well as fertility. The altered phenotypes observed in the mutants display non-mendelian inheritance though the primary cause of the alteration is the mutation at a chromosomal locus ( chm) in linkage group 3. The two mutants seem allelic but non-identical. The results of the genetic analysis are consistent with the interpretation that a nuclear mutator locus is inducing several different type of hereditary alterations in the plastome. The plastome mutations reveal involvement of the plastome in the control of its own morphology as well as in cellular and organ differentiation. The system indicates that though the plastome is endowed with a considerable autonomy in some functions its mutability is subject also to nuclear control. The informational content of the 20–80 plastids per cell is apparently identical. The occurrence of cells with different types of plastids reveals that “epistasis” is not of major importance among the plastids within a single cell. The independent expression and inheritance of color variegation from morphological alterations indicate a separate localization (absence of linkage) of the pertaining genetic elements. The predominantly joint appearance of other phenes point to the existence of pleiotropy or linkage within the plastids.