DETECTION OF DELETERIOUS GENOTYPES IN MULTIGENERATIONAL STUDIES - I -DISRUPTIONS IN INDIVIDUAL ARABIDOPSIS ACTIN GENES

Plant actins are involved in numerous cytoskeletal processes effecting plant development, including cell division plane determination, cell elongation, and cell wall deposition. Arabidopsis thaliana has five an cient subclasses of actin with distinct patterns of spatial and tempor al expression. To test their functional roles, we identified insertion mutants in three Arabidopsis actin genes, ACT2, ACT4, and ACT7 repres enting three subclasses. Adult plants homozygous for the act2-1, act4- 1, and act7-1 mutant alleles appear to be robust, morphologically norm al, and fully fertile. However, when grown as populations descended fr om a single heterozygous parent, all three mutant alleles were found a t extremely low frequencies relative to the wild-type in the F-2 gener ation. Thus, all three mutant alleles appear to be deleterious. The ac t2-1 mutant allele was found at normal frequencies in the F-1, but at significantly lower frequencies than expected in the F-2 and F-3 gener ations. These data suggest that the homozygous act2-1/act2-2 mutant ad ult plants have a reduced fitness in the 2N sporophytic portion of the life cycle, consistent with the vegetative expression of ACT2. These data are interpreted in light of the extreme conservation of plant act in subclasses and genetic redundancy.