Lignin and flavonoid depositions in the cell walls of CHS-, CHI-, and CHIL-deficient rice mutant lines. Transverse sections of culm tissues were subjected to phloroglucinol–HCl staining and vanillin–HCl staining, which stain monolignol-derived lignins and cell wall-bound flavonoids, respectively. Scale bars denote 40 µm. OsCHS1-TDNA, OsCHS1 knockout line (cv. Zhonghua 11); OsCHI-CRISPR-a, OsCHI knockout line (cv. Nipponbare); OsCHIL-CRISPR-a, OsCHIL1 and OsCHIL2 double-knockout line (cv. Nipponbare).