Polymerization-mediated SRFR1 condensation in upper lateral root cap cells regulates root growth

Plant growth and development depend on precise responses to environmental and developmental cues. Primary root growth, regulated by internal hormone signals, must adapt to external factors such as water availability, soil compactness, pH, and microbial interactions. An essential step in root growth consists of cell divisions in the meristem, with outermost root cap layer thought to provide protection. However, recent studies reveal that lateral root cap (LRC) cells play critical regulatory roles beyond protection. In this study, we identified an LRC-specific protein condensation mechanism governing root growth. We demonstrated that SRFR1 forms condensates specifically in upper LRCs and their accumulation is dynamically modulated by both growth conditions and hormone treatment. SRFR1 condensate formation is driven by its plant-associated N-terminal tetratricopeptide repeat (PANT) polymerization domain and finetuned by the adjacent intrinsically disordered region 1 (IDR1). Mutational and biophysical analyses show that IDR1’s zwitterionic nature is essential for its regulatory role, acting as a chaperone to promote PANT polymerization at low temperatures while preventing aggregation at high temperatures. This enables SRFR1 condensate formation across a wide temperature range. Notably, the zwitterionic IDR1 can be functionally substituted by zwitterionic dehydrins. Shifting IDR1 towards a negative state impairs condensate formation, whereas a positive shift enhances SRFR1 condensation and further improves root growth. The association of zwitterionic IDRs with polymerization domains is common, suggesting that this mechanism broadly prevents irreversible aggregation and promotes physiological polymerization under varying temperatures.