Dynamical Modeling of the Core Gene Network Controlling Flowering Suggests Cumulative Activation From the Gene Homologs in Chickpea.

Initiation of flowering moves plants from vegetative to reproductive development. The time when this transition happens (flowering time), an important indicator of productivity, depends on both endogenous and environmental factors. The core genetic regulatory network canalizing the flowering signals to the decision to flower has been studied extensively in the model plant and has been shown to preserve its main regulatory blocks in other species. It integrates activation from the () gene or its homologs to the flowering decision expressed as high expression of the meristem identity genes, including . We elaborated a dynamical model of this flowering gene regulatory network and applied it to the previously published expression data from two cultivars of domesticated chickpea (), obtained for two photoperiod durations. Due to a large number of free parameters in the model, we used an ensemble approach analyzing the model solutions at many parameter sets that provide equally good fit to data. Testing several alternative hypotheses about regulatory roles of the five homologs present in chickpea revealed no preference in segregating individual copies as singled-out activators with their own regulatory parameters, thus favoring the hypothesis that the five genes possess similar regulatory properties and provide cumulative activation in the network. The analysis reveals that different levels of activation from can explain a small difference observed in the expression of the two homologs of the repressor gene . Finally, the model predicts highly reduced activation between and , thus suggesting that this regulatory block is not conserved in chickpea and needs other mechanisms. Overall, this study provides the first attempt to quantitatively test the flowering time gene network in chickpea based on data-driven modeling.