FLEXIBLE CULM 1 encoding a cinnamyl-alcohol dehydrogenase controls culm mechanical strength in rice

Culm mechanical strength is an important agronomic trait in crop breeding. To understand the molecular mechanisms that control culm mechanical strength, we identified a flexible culm1 (fc1) mutant by screening a rice T-DNA insertion mutant library. This mutant exhibited an abnormal development phenotype, including late heading time, semi-dwarf habit, and flexible culm. In this study, we cloned the FLEXIBLE CULM1 (FC1) gene in rice using a T-DNA tagging approach. FC1 encodes a cinnamyl-alcohol dehydrogenase and is mainly expressed in the sclerenchyma cells of the secondary cell wall and vascular bundle region. In these types of cells, a deficiency of FC1 in the fc1 mutant caused a reduction in cell wall thickness, as well as a decrease in lignin. Extracts from the first internodes and panicles of the fc1 plants exhibited drastically reduced cinnamyl-alcohol dehydrogenase activity. Further histological and biochemical analyses revealed that the p-hydroxyphenyl and guaiacyl monomers in fc1 cell wall were reduced greatly. Our results indicated that FC1 plays an important role in the biosynthesis of lignin and the control of culm strength in rice.