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

Katie Abley,Pau Formosa-Jordan,Hugo Tavares,Ottoline Leyser,Emily YT Chan,James CW Locke,Mana Afsharinafar

doi:10.7554/elife.59485

Abstract

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.

Highlights

In an environment where current cues cannot be used to predict future conditions, exhibiting a range of phenotypes may promote species survival
To understand further how differences in coefficient of variation (CV) and mode of germination time distributions are generated by the model, we looked across all the parameter screen results to see how CV and mode varied as the model switched between the situation where the model is monostable after the rise in gibberellic acid (GA) production (e.g. Figure 5—figure supplement 1A–G) and the situation where it is bistable following this rise in GA production (e.g. Figure 5—figure supplement 1H–U)
By describing detailed distributions of germination time for hundreds of Arabidopsis lines grown in a common environment, our work reveals that these distributions are genetically controlled since they can vary greatly between different lines and are reproducible for a given genotype

Summary

Introduction

In an environment where current cues cannot be used to predict future conditions, exhibiting a range of phenotypes may promote species survival. A combination of experiment and modelling has revealed that the ABA-GA network can be described as a bistable switch due to the mutual inhibition between ABA and GA, leading to two possible states, a dormant high ABA low GA state, or a germinating low ABA high GA state (Topham et al, 2017) This regulatory motif can explain the observation that Arabidopsis seed germination is more effectively triggered by fluctuating temperatures than continuous cold (Topham et al, 2017). Our work reveals the degree of variability in germination time in Arabidopsis as well as evidence for its genetic basis and provides a starting point for future work examining the mechanisms of phenotypic variability in seed germination time

Results

Discussion

Materials and methods

Data availability statement