CRISPR-BASED IMPROVEMENT OF FORAGE DIGESTIBILITY: TARGETING LIGNIN PATHWAYS IN NAPIER GRASS AND MAIZE

Abstract

This review examines the potential of CRISPR-based genome editing to improve forage digestibility by modifying lignin biosynthesis in two major C4 grasses, maize (Zea mays L.) and Napier grass (Cenchrus purpureus). Lignin is essential for plant structure, water transport, lodging resistance, and stress adaptation, but it also reduces cell-wall digestibility by limiting microbial and enzymatic access to polysaccharides. In grasses, this challenge is intensified by hydroxycinnamate-mediated cross-linking and the complexity of secondary cell walls. The review synthesizes recent evidence on lignin biosynthetic genes, including PAL, C4H, 4CL, HCT/C3H, CCoAOMT, CCR, F5H, COMT, and CAD, and discusses how editing these targets may alter lignin amount, composition, and cross-linking. A focused comparison is made between maize, where classical brown-midrib mutants and newer genome-editing studies provide a stronger mechanistic foundation, and Napier grass, where genomic resources are improving but functional validation and transformation remain limited. The review methodology is explicitly defined through database searching, screening, and evidence synthesis to address common weaknesses in narrative review writing. Overall, the evidence suggests that moderate, precisely targeted editing of lignin pathways is more promising than drastic lignin reduction, because digestibility gains must be balanced against biomass yield, structural integrity, and stress tolerance. The review concludes that multiplex and regulatory editing strategies, combined with transcriptomic and phenotypic validation, offer the most realistic path for developing high-digestibility forage ideotypes in maize and, in the longer term, Napier grass.