MeGT2.6 increases cellulose synthesis and active gibberellin content to promote cell enlargement in cassava

SUMMARY Cassava, a pivotal tropical crop, exhibits rapid growth and possesses a substantial biomass. Its stem is rich in cellulose and serves as a crucial carbohydrate storage organ. The height and strength of stems restrict the mechanised operation and propagation of cassava. In this study, the triple helix transcription factor MeGT2.6 was identified through yeast one‐hybrid assay using MeCesA1pro as bait, which is critical for cellulose synthesis. Over‐expression and loss‐of‐function lines were generated, and results revealed that MeGT2.6 could promote a significant increase in the plant height, stem diameter, cell size and thickness of SCW of cassava plant. Specifically, MeGT2.6 upregulated the transcription activity of MeGA20ox1 and downregulated the expression level of MeGA2ox1, thereby enhancing the content of active GA3, resulting in a large cell size, high plant height and long stem diameter in cassava. Moreover, MeGT2.6 upregulated the transcription activity of MeCesA1, which promoted the synthesis of cellulose and hemicellulose and produced a thick secondary cell wall. Finally, MeGT2.6 could help supply additional substrates for the synthesis of cellulose and hemicellulose by upregulating the invertase genes (MeNINV1/6). Thus, MeGT2.6 was found to be a multiple regulator; it was involved in GA metabolism and sucrose decomposition and the synthesis of cellulose and hemicellulose. Significance Statement Schematic of the increase in cellulose synthesis and active gibberellin content to promote cell enlargement via the modulation of MeGT2.6. UDP‐Glc: Uridine diphosphate glucose; CSC: cellulose synthase complex; SCW: secondary cell wall. Cassava is a tropical root crop with huge biomass. Increasing the allocation of photoassimilate to the sink organ can enhance the yield of storage root. MeGT2.6 is a multi‐regulatory factor regulating plant growth and development, and carbon source allocation. Its mutant can be created by gene editing, thereby providing an important germplasm resource for breeding new cassava varieties with dwarf property and high starch yield.