Artificial intelligence-based structural modeling of PSTOL1 receptor kinases in rice and sorghum.

Originally identified in rice (Oryza sativa OsPSTOL1), PHOSPHORUS-STARVATION TOLERANCE 1 (PSTOL1) proteins are essential determinants of phosphorus efficiency in several plant species, including Sorghum bicolor (SbPSTOL1). In contrast to OsPSTOL1, SbPSTOL1 homologs exhibit a transmembrane receptor-like kinase (RLK) architecture with polymorphic extracellular domains. We employed an AI-driven computational pipeline to investigate the structure and conformational dynamics of SbPSTOL1 proteins. Monomeric predictions using multiple deep-learning platforms yielded structures that were inconsistent with the SbPSTOL1 RLK topology, suggesting inherent monomeric instability or autoinhibition. In a validation step, we also modeled the phylogenetically related ZmWAKL RLK, which forms a heterodimer with its likely co-receptor, ZmWIK, and reproduced their interaction in silico. Oligomeric modelling resulted in structurally plausible models for SbPSTOL1 proteins that overcame the structural monomeric instability. Molecular dynamics simulations in a membrane environment also supported the preferential stability of oligomeric SbPSTOL1 states. Regional analysis suggested that, while the transmembrane and kinase domains are more rigid, the extracellular regions exhibit higher flexibility, consistent with their roles in environmental perception. Notably, oligomerization was associated with a conformational transition in the catalytic site, likely enabling the formation of the canonical αC-Glu ↔ β3-Lys salt bridge, a hallmark of kinase activation. Altogether, these results support a model in which oligomerization is a probable structural prerequisite for the catalytic competence of SbPSTOL1 but not necessarily of OsPSTOL1. These AI-based findings represent testable hypotheses for future experimental validation and present the first in silico structural characterization of SbPSTOL1 proteins, offering insights for elucidating complex RLK-mediated plant signaling mechanisms.