Integrative molecular mechanisms of lodging resistance in rice (Oryza sativa L.) culms: from DELLA-OsGSK2-BZR1 signaling to cell wall engineering and QTL-based breeding.

Rice lodging, permanent culm displacement from the vertical position, reduces grain yield and quality, potentially causing up to ~80% yield loss. Lodging resistance is a multifactorial trait shaped by stem morphology, internal anatomy, and cell wall chemistry. A central unresolved question in the field concerns the relative contribution of lignin versus cellulose to culm mechanical strength, a debate that has significant implications for targeted breeding and cell wall engineering. This review offers a comprehensive integration of two key questions: (1) What are the current molecular regulatory mechanisms underlying lodging resistance-associated culm traits in rice? (2) How can these mechanisms be translated into effective breeding strategies?. How can these mechanisms be translated into effective breeding strategies? Unlike earlier reviews that focused on individual mechanisms, this synthesis integrates hormonal crosstalk, hierarchical NAC-MYB cascades, emerging evidence for epigenetic regulation, and QTL-based breeding into a unified conceptual framework centered on the DELLA-OsGSK2-BZR1 module. Our synthesis reveals that plant architecture is governed by extensive phytohormone crosstalk centered on the proposed DELLA-OsGSK2-BZR1 module, where gibberellin and brassinosteroid synergistically modulate elongation and thickening, whereas auxin, strigolactone, ethylene, and jasmonic acid fine-tune plant height and tillering. Major-effect loci, such as SCM2/APO1 and SCM3/OsTB1, enable the concurrent improvement of strength and yield, with QTL pyramiding reported to increase culm diameter by up to ~39% in specific genetic backgrounds. Vascular bundle development and cell wall biosynthesis (lignin, cellulose, and hemicellulose) are coordinated by hierarchical NAC-MYB transcriptional cascades, with recent advances suggesting epigenetic regulation through DNA methylation, histone modification, and DELLA-mediated chromatin silencing in rice. We further discuss how these mechanistic insights may guide modern breeding through marker-assisted selection, genome selection, CRISPR/Cas9-mediated precision engineering, and ideotype design, providing a roadmap for developing next-generation lodging-resistant rice varieties.