An ABA-GA bistable switch can account for natural variation in the variability of Arabidopsis seed germination time

Genetically identical plants growing in the same conditions can display heterogeneous phenotypes. Here we use Arabidopsis seed germination time as a model system to examine phenotypic variability and its underlying mechanisms. We show extensive variation in seed germination time variability between Arabidopsis accessions and use a multiparent recombinant inbred population to identify two genetic loci involved in this trait. Both loci include genes implicated in modulating abscisic acid (ABA) sensitivity. Mutually antagonistic regulation between ABA, which represses germination, and gibberellic acid (GA), which promotes germination, underlies the decision to germinate and can act as a bistable switch. A simple stochastic model of the ABA-GA network shows that modulating ABA sensitivity can generate the range of germination time distributions we observe experimentally. We validate the model by testing its predictions on the effects of exogenous hormone addition. Our work provides a foundation for understanding the mechanism and functional role of phenotypic variability in germination time.

Automated summary

Genetically identical plants can display heterogeneous phenotypes under the same conditions, and a study on Arabidopsis seed germination time has revealed the underlying mechanisms of this phenotypic variability. The research identified genetic loci and genes involved in modulating abscisic acid sensitivity, showing that the ABA-GA network acts as a bistable switch in the decision to germinate. A simple stochastic model of this network was validated through experimental observations, providing a foundation for understanding phenotypic variability in germination time.