Ethylene signaling via Ethylene Response Factors (ERFs) modifies wood development in hybrid aspen

Background The phytohormone ethylene (ET) has the potential to regulate secondary growth of plants and wood formation in trees. Application of exogenous ethylene or its in planta precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), to wood forming tissues of hybrid aspen (Populus tremula x Populus tremuloides) enhances xylem growth [1]. In the same study it was demonstrated that stimulation of enhanced xylem formation (tension wood, TW) at the upper side of leaning stems is mediated by endogenous ET. The production of endogenous ET in TW forming tissues is further supported by the increase of ACC oxidase gene transcript and enzyme activity on the TW side [2]. The ET perception and signal transmission cascade in Arabidopsis has been linked to the transcriptional activation of Ethylene Response Factors (ERFs) [3,4]. As transcription factors, ERFs regulate the expression of various specific downstream target genes by binding to cis-elements in their promoters [5]. We hypothesize that ERFs participate in xylem development through ethylene signaling and that they are involved in ET responses during TW formation.