Root growth in Arabidopsis requires gibberellin/DELLA signalling in the endodermis

Gibberellins ( Gas) are key regulators of plant growth and development. they promote growth by targeting the degradation of DELLA repressor proteins; however, their site of action at the cellular, tissue or organ levels remains unknown. to map the site of GA action in regulating root growth, we expressed gai, a non-degradable, mutant DELLA protein, in selected root tissues. root growth was retarded specifically when gai was expressed in endodermal cells. our results demonstrate that the endodermis represents the primary GA-responsive tissue regulating organ growth and that endodermal cell expansion is rate-limiting for elongation of other tissues and therefore of the root as a whole.