Plant class III heme peroxidases catalyze lignin polymerization. Previous reports have shown that at least three Arabidopsis thaliana peroxidases, AtPrx2, AtPrx25 and AtPrx71, are involved in stem lignification using T-DNA insertion mutants, atprx2, atprx25, and atprx71. Here, we generated three double mutants, atprx2/atprx25, atprx2/atprx71, and atprx25/atprx71, and investigated the impact of the simultaneous deficiency of these peroxidases on lignins and plant growth. Stem tissue analysis using the acetyl bromide method and derivatization followed by reductive cleavage revealed improved lignin characteristics, such as lowered lignin content and increased arylglycerol-β-aryl (β-O-4) linkage type, especially β-O-4 linked syringyl units, in lignin, supporting the roles of these genes in lignin polymerization. In addition, none of the double mutants exhibited severe growth defects, such as shorter plant stature, dwarfing, or sterility, and their stems had improved cell wall degradability. This study will contribute to progress in lignin bioengineering to improve lignocellulosic biomass.
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