AGP Glycosylation Controls Cell Wall Signal Integration During Development in Arabidopsis

Background Arabinogalactan proteins (AGPs) are hydroxyproline-rich glycoproteins essential for plant cell wall dynamics, signaling, vegetative growth, and reproductive development. Their initial glycosylation is catalyzed by eight hydroxyproline- O -galactosyltransferases (GALT2-GALT9) in Arabidopsis thaliana . However, the early molecular consequences of defective AGP galactosylation and how they vary across developmental stages remain poorly understood. Results RNA-sequencing of the galt2-9 octuple mutant revealed stage-dependent transcriptomic reprogramming across whole seedlings, early stage flowers, and early stage siliques. Seedlings showed modest changes (646 DEGs), with enrichment of hemicellulose/xyloglucan metabolism, lignin, and suberin biosynthesis pathways. Early stage flowers exhibited intermediate reprogramming (1,466 DEGs), activating pollen tube guidance, fertilization, and stress signaling pathways. Early stage siliques displayed extensive transcriptional changes (5,856 DEGs), strongly inducing defense pathways, including chitin catabolism, camalexin biosynthesis, pathogen-associated molecular pattern (PAMP) recognition, and seed oil-body formation. At maturity, siliques exhibited near-complete transcriptional compensation (99.97% normalization), driven by upregulation of ethylene response factors, receptor kinases, and WRKY transcription factors, whereas flowers accumulated persistent defects in pollen maturation genes. Weighted gene co-expression network analysis (WGCNA) identified distinct AGP-associated modules across developmental stages. In seedlings, AGP5 co-expressed with stress- and cell wall-related genes including GSTF6, GSTF7, WRKY41, and RLP28, while AGP13 and AGP14 associated with cell wall remodeling components. In early stage flowers, AGP5 was linked to signaling genes such as CHI, PNP-A, and RLP23, and pollen-related AGP6 and AGP11 formed reproductive modules with VGDH1, PRK2A, and RALFL4. In early stage siliques, AGP2 and AGP23 co-expressed with genes involved in transport, metabolism, and silique-specific developmental processes. Gene ontology enrichment further highlighted tissue-specific compensatory programs, with seedlings prioritizing structural reinforcement, flowers activating reproductive signaling networks, and siliques mounting strong defense and metabolic responses. Conclusion These findings demonstrate that impaired AGP glycosylation triggers highly stage- and tissue-specific transcriptomic adaptations, with differential compensatory capacities across development. While core developmental programs remain largely intact, AGP deficiency reduces the efficiency and completeness of their execution, particularly in reproductive tissues. AGPs therefore function as modulators of developmental program efficiency and fidelity, linking cell wall architecture with signaling networks that regulate defense, metabolism, and reproduction. The identification of stage-specific AGP-associated gene networks provides a transcriptomic framework for understanding how glycan-dependent cell surface interactions are associated with plant developmental transitions. These results identify candidate regulatory modules and molecular markers for future functional validation and provide a foundation for future efforts to target AGP-mediated pathways in crop improvement strategies aimed at optimizing growth, stress resilience, and reproductive success.