The plant hormone ethylene restricts Arabidopsis growth via the epidermis

Significance

Ethylene is a gaseous hormone that controls plant life throughout development. Being a simple hydrophobic molecule, it can freely enter cells; therefore, the cell type specificity of its action is challenging. By means of tissue-specific expression of two negative regulators of the signaling cascade, we selectively disrupted the ethylene signal in different cell types without affecting its biosynthesis. We demonstrate that ethylene restricts plant growth by dampening the effect of auxins in the outermost cell layer. We further show that this epidermis-specific signaling has an impact on the growth of neighboring cells, suggesting that the master controller of cell expansion resides in the epidermis, where it senses the environment and, subsequently drives growth, of the inner tissues.

Abstract

The gaseous hormone ethylene plays a key role in plant growth and development, and it is a major regulator of stress responses. It inhibits vegetative growth by restricting cell elongation, mainly through cross-talk with auxins. However, it remains unknown whether ethylene controls growth throughout all plant tissues or whether its signaling is confined to specific cell types. We employed a targeted expression approach to map the tissue site(s) of ethylene growth regulation. The ubiquitin E3 ligase complex containing Skp1, Cullin1, and the F-box protein EBF1 or EBF2 (SCF ^EBF1/2) target the degradation of EIN3, the master transcription factor in ethylene signaling. We coupled EBF1 and EBF2 to a number of cell type-specific promoters. Using phenotypic assays for ethylene response and mutant complementation, we revealed that the epidermis is the main site of ethylene action controlling plant growth in both roots and shoots. Suppression of ethylene signaling in the epidermis of the constitutive ethylene signaling mutant ctr1-1 was sufficient to rescue the mutant phenotype, pointing to the epidermis as a key cell type required for ethylene-mediated growth inhibition.