STF, A WOX Family Transcript Factor, Regulates Leaf Development And Functions Of MtCKX In Medicago Truncatula

In higher plants, the leaf blade is the central energy convertor.STENOFOLIA (STF), a WOX family transcription factor and the leaf blade development regulator, was introduced into grasses switchgrass,Brachypodium and rice, significantly improves biomass yield. We found the biomass increase was attributed mainly to increased leaf width and stem thickness, which was appeared to be caused by enhanced cell proliferation.STF directly binds to multiple regions in the promoters of several cytokinin oxidase/dehydrogenase (CKX) genes in vitro and in vivo and represses their expression in all the three transgenic grasses. This repression was accompanied by a significant increase in active cytokinin content in transgenic rice leaves, suggesting that STF promotes biomass productivity by increasing active cytokinins through direct repression of cytokinin degrading enzymes. Meanwhile, we found 9 MtCKXs in medicago truncatula whose expressional pattern are distinct. Expression levels of MtCKXs were induced by cytokinin (6-BA) obviousely.MtCKX4B, a member of MtCKX family, expressed in roots peculiarly, functions in root architecture. Our study provides a new tool for improving biomass feedstock yield in bioenergy crops,and uncovers a novel mechanistic insight in the function of STF and repressive CKX genes that are master regulators of several key plant developmental programs.