The novel Arabidopsis thaliana svt2 suppressor of the ascorbic acid-deficient mutant vtc1-1 exhibits phenotypic and genotypic instability

Ascorbic acid is a potent antioxidant that detoxifies reactive oxygen species when plants are exposed to unfavorable environmental conditions. In addition to its antioxidant properties, ascorbic acid and its biosynthetic precursors fulfill a variety of other physiological and molecular functions. A mutation in the ascorbic acid biosynthesis gene VTC1, which encodes GDP-mannose pyrophosphorylase, results in conditional root growth inhibition in the presence of ammonium. To isolate suppressors of vtc1-1, which is in the Arabidopsis Columbia-0 background, seeds of the mutant were subjected to ethyl methanesulfonate mutagenesis. A suppressor mutant of vtc1-1 2, svt2, with wild-type levels of ascorbic acid and root growth similar to the wild type in the presence of ammonium was isolated. Interestingly, svt2 has Arabidopsis Landsberg erecta features, although svt2 is delayed in flowering and has an enlarged morphology. Moreover, the svt2 genotype shares similarities with L er polymorphism markers and sequences, despite the fact that the mutant derived from mutagenesis of Col-0 vtc1-1 seed. We provide evidence that svt2 is not an artifact of the experiment, a contamination of L er seed, or a result of outcrossing of the svt2 mutant with L er pollen. Instead, our results show that svt2 exhibits transgenerational genotypic and phenotypic instability, which is manifested in a fraction of svt2 progeny, producing revertants that have Col-like phenotypic and genotypic characteristics. Some of those Col-like revertants then revert back to svt2-like plants in the subsequent generation. Our findings have important implications for undiscovered phenomena in transmitting genetic information in addition to the Mendelian laws of inheritance. Our results suggest that stress can trigger a genome restoration mechanism that could be advantageous for plants to survive environmental changes for which the ancestral genes were better adapted.