Lignin and cellulose synthesis and antioxidative defense mechanisms are affected by light quality in Brachypodium distachyon

Light quality is perceived by plants through several receptors and generates diverse morphological, metabolic, and genetic responses. In this study, the identification of new putative lignocellulosic genes, expression analysis, as well as morphological, anatomical, enzymatic, and chemical characteristics were investigated in Brachypodium distachyon plants grown in vitro under different light treatments. Treatments with fluorescent lamps (FL), white light-emitting diode (LED) bulbs, and blue/red (B/R) LED bulbs showed different effects on B. distachyon, acting on specific targets to promote functional adaptation. The FL, traditionally used in growth rooms, led to higher growth rates and deposition of S and G lignins, greater cellulose content, and higher expression of cellulose-synthase 4 (BbCESA4) and cellulose-synthase 7 (BdCESA7) genes. Phenylalanine ammonia-lyase (BdPAL1) and ferulate-5-hydroxylase (BdF5H1) genes were upregulated in plants exposed to B/R LED light when compared to those grown under FL and white LED light, while other analyzed genes did not vary in expression among treatments. BdCESA4 was downregulated under B/R LED light, light quality that led to smaller plants, with increased lignin content, higher abundance of G lignin than S lignin, and decreased total cellulose content compared to the other treatments. In white LED light, both BdCESA4 and BdCESA7 were downregulated compared to FL, in addition to a significant increase in superoxide dismutase (SOD) and catalase (CAT) activities. The spectral quality of the LED bulbs altered lignin and cellulose contents, expression of their synthesis-route genes, as well as anatomical and antioxidative defense mechanisms. These results suggest that light quality regulates cell wall deposition and lignification patterns in B. distachyon