Brassinosteroid induction of AtACS4 encoding an auxin‐responsive 1‐aminocyclopropane‐1‐carboxylate synthase 4 in Arabidopsis seedlings

Brassinosteroid (BR), an endogenous steroid growth regulator of higher plants, enhances expansion and division of the cell in a number of plant species. It has been recently reported that a shared auxin–BR signalling pathway is involved in the seedling growth in . Here, we show that BR specifically enhanced the expression of , which encodes an auxin‐responsive ACC synthase 4, by a distinct temporal induction mechanism compared with that of IAA in etiolated seedlings. This BR induction of was undetectable in the light‐grown seedlings. In addition, BR failed to activate the gene in () and (), both of which are auxin‐resistant mutants. Thus, it appears that there is a possible regulatory link between light, auxin and BR to control ethylene synthesis in young seedlings. Analysis of transgenic plants harbouring fusion revealed the promoter‐driven GUS activity in the highly elongating zone of the hypocotyls in response to BR treatment. Furthermore, plants homozygous for the T‐DNA insertion in the gene exhibited longer hypocotyls and roots than those of control seedlings. Taken together, these results suggest that the BR‐induced ethylene production may participate in the elongation growth response in early seedling development of .

Duke Scholars

Author Eunyu Kim DKU Faculty