Distinct root apoplastic barrier distribution and conserved peroxidase function in desert trees

The formation of extracellular barriers in roots plays a critical role in maintaining water balance and nutrient homeostasis; however, their molecular composition and physiological roles in desert-adapted plants remain largely unexplored.Here, we examine apoplastic barrier formation in the roots of two arid-adapted, ecologically and economically important tree species: date palm (Phoenix dactylifera) and grey mangrove (Avicennia marina). In date palm, lignin and suberin showed complementary distribution patterns within the outer root layers. In mangrove roots, lignin accumulated in the epidermis and exodermis, whereas suberin was concentrated in the exodermis. Label-free Raman spectroscopy imaging confirmed these spatial patterns. Noninvasive Magnetic resonance imaging (MRI) revealed that water distribution mirrored barrier localization: date palms retained water in the vasculature and outer tissues, whereas mangroves concentrated water in the xylem. Transcriptome analysis identified a type III PEROXIDASE (PER) highly expressed in the exodermis of both species. The PER protein localized to Golgi-derived vesicles and the plasma membrane and interacted with a component of the Golgi apparatus. Expression of date palm and mangrove PER in Arabidopsis thaliana leads to ectopic lignin deposition in the root epidermis. Together, our findings suggest that type III PEROXIDASES are transported to the plasma membrane through the Golgi vesicles and promote lignin deposition. Overall, this study reveals distinct root barrier distribution and identifies a conserved molecular component underlying structural adaptations that enable plants to thrive in challenging environments.