Regulation of lignin biosynthesis by <scp>GhCAD37</scp> affects fiber quality and anther vitality in upland cotton

Cotton stands as a pillar in the textile industry due to its superior natural fibers. Lignin, a complex polymer synthesized from phenylalanine and deposited in mature cotton fibers, is believed to be essential for fiber quality, although the precise effects remain largely unclear. In this study, we characterized two ubiquitously expressed cinnamyl alcohol dehydrogenases (CAD), GhCAD37A and GhCAD37D (GhCAD37A/D), in Gossypium hirsutum. GhCAD37A/D possess CAD enzymatic activities, to catalyze the generation of monolignol products during lignin biosynthesis. Analysis of transgenic cotton knockout and overexpressing plants revealed that GhCAD37A/D are important regulators of fiber quality, positively impacting breaking strength but negatively affecting fiber length and elongation percentage by modulating lignin biosynthesis in fiber cells. Moreover, GhCAD37A/D are shown to modulate anther vitality and affect stem lodging trait in cotton by influencing lignin biosynthesis in the vascular bundles of anther and stem, respectively. Additionally, our study revealed that Ghcad37A/D knockout plants displayed red stem xylem, likely due to the overaccumulation of aldehyde intermediates in the phenylpropanoid metabolism pathway, as indicated by metabolomics analysis. Thus, our work illustrates that GhCAD37A/D are two important enzymes of lignin biosynthesis in different cotton organs, influencing fiber quality, anther vitality, and stem lodging.