GPAT2 is required for root cap cuticle formation in young Arabidopsis seedlings

During seedling establishment, a cuticle protects the root cap until the outer embryonic cell layer is shed. In Arabidopsis, the root cap cuticle of primary roots has a distinct composition that includes ester-bound unsubstituted very-long-chain fatty acids (VLCFAs) and ester-bound oxygenated C16/C18 fatty acids. We show that the incorporation of C26/C28 VLCFAs depends on the sn2-glycerol-3-phosphate acyltransferase GPAT2. Loss of GPAT2 increases cuticle permeability and enhances mucilage attachment while only moderately altering cuticle ultrastructure. In contrast, loss of the long-chain acyl-coenzyme A (CoA) synthetase LACS2-which functions with GPAT4 and GPAT8 to incorporate only oxygenated fatty acids into cutin-causes severe ultrastructural and barrier defects but has little effect on mucilage attachment. These findings reveal two largely independent pathways-GPAT2 dependent and LACS2/GPAT4/GPAT8 dependent-that differentially shape root cap cuticle structure and barrier function. Overall, this study provides new insights into organ-specific pathways of plant cuticle biosynthesis.