Drought is one of the major environment factors that threatens future food security. In plants, stomatal pores expel 200 molecules of water for every carbon-dioxide molecule that is fixed during photosynthesis. Under drought conditions, plant hormone abscisic acid (ABA) activates its receptors, eventually leading to stomata closure and reduced water loss. Therefore, it is critical to understand the molecular process behind perceptions of plant hormones that regulate opening and closing of guard cells. In a recent study from our group published in Structure, we describe the mechanism of plant hormone perception that leads to initiation of drought resistance signaling.

Since 2009, several ABA-mimicking agrochemicals such as pyrabactin and quinabactin were discovered which can target ABA receptors. Chemical control of ABA receptors is thereby a promising strategy to modulate plant drought tolerance.

Despite progresses in understanding ABA signaling, a complete molecular picture of ABA recognition by the receptors is still lacking. Our study uses atomistic simulations to investigate ABA-mediated activation of two subtype ABA receptors from Arabidopsis thaliana. We have identified the pathways and the energetic landscapes of ABA binding and receptor activations, leading to unique insights into hormone perception.

The video depicts the process of plant hormone (ABA) binding to its receptor. The plot on the left shows the free energy landscapes associated with the process. Free energy indicates the probability of observing a particular conformation of the ligand and protein.

Interestingly, we have found that ABA binding is a necessary but insufficient condition for full receptor activation. A large energy barrier for ABA binding is observed, which is associated with the exclusion of water molecules from the receptor binding pocket.

Our results also show that post-translational modification of ABA receptor prevents ABA binding and renders current agrochemicals ineffective on ABA receptor activation.

Our findings open up new possibility for selective modulation of ABA receptors and design of new agrochemicals for effective control of drought resistance in plants.  

The paper is available online on the cell press website.