Chilling-induced accumulation of reactive oxygen species (ROS) is harmful to plants, which usually produce anthocyanins to scavenge ROS as protection from chilling stress. As a tropical crop, cassava is hypersensitive to chilling, but the biochemical basis of this hypersensitivity remains unclear. We previously generated MeMYB2-RNAi transgenic cassava with increased chilling tolerance. Here we report that MeMYB2-RNAi transgenic cassava accumulated less ROS but more cyanidin-3-O-glucoside than the wild type under early chilling stress. Under this stress, the anthocyanin biosynthesis pathway was more active in MeMYB2-RNAi lines than in the wild type, and several genes involved in the pathway, including MeTT8, were up-regulated by MeMYB2-RNAi in the transgenic cassava. MeMYB2 bound to the MeTT8 promoter and blocked its expression under both normal and chilling conditions, thereby inhibiting anthocyanin accumulation. MeTT8 was shown to bind to the promoter of Dihydroflavonol 4-reductase (MeDFR-2) and increased MeDFR-2 expression. MeMYB2 appears to act as an inhibitor of chilling-induced anthocyanin accumulation during the rapid response of cassava to chilling stress.

Drought stress impairs plant growth and other physiological functions. MeHDZ14, a homeodomain-leucine zipper Ⅰ transcription factor, is strongly induced by drought stress in various cassava cultivars. However, the role of MeHDZ14 in cassava growth regulation has remained unclear. Here we report that MeHDZ14 affected plant height, such that a dwarf phenotype and altered internode elongation were observed in transgenic cassava lines. MeHDZ14 was found to negatively regulate the biosynthesis of lignin. Its overexpression resulted in abaxially rolled leaves. The morphogenesis of leaf epidermal cells was inhibited by overexpression of MeHDZ14, with decreased auxin and gibberellin and increased cytokinin contents. MeHDZ14 was found to regulate many drought-responsive genes, including genes involved in cell wall synthesis and expansion. MeHDZ14 bound to the promoter of caffeic acid 3-O-methyltransferase 1 (MeCOMT1), acting as a transcriptional repressor of genes involved in cell wall development. MeHDZ14 appears to act as a negative regulator of internode elongation and epidermal cell morphogenesis during cassava leaf development.