Transcriptional regulation of ethylene biosynthesis and signaling genes in sugarcane

Abstract

Ethylene is a gaseous plant hormone involved in many phases of development and in responses to biotic and abiotic stresses. In sugarcane fields, the application of ethylene precursors accelerates the ripening process and inhibits flowering. In plant cells, the ACS (ACC synthase) and ACO (ACC oxidase) enzymes catalyze the ethylene production, which is perceived by a group of receptors triggering a signaling cascade and resulting in the activation and repression of transcription factors. The sugarcane genes encoding ethylene biosynthesis and signaling proteins and their transcriptional regulation are barely known. The major aim of this work was to characterize the transcriptional regulators of the ScACS2 gene, encoding an ACS from sugarcane. Three bHLH (Basic Helix-loop-Helix) transcription factors from the FBH (FLOWERING BHLH) subfamily were isolated by their ability to bind in the promoter of ScACS2 gene. These factors are more expressed in maturing internodes where they activate ScACS2 expression as homo-and heterodimers. Functional studies in Arabidopsis demonstrated that FBHs control ethylene biosynthesis regulating ACS transcription, suggesting that this mechanism is conserved across plant species. We also aimed to identify the key genes involved in ethylene biosynthesis and evaluate their regulation in sugarcane. We identified several other members of ethylene biosynthesis and signaling pathways, homologs of Arabidopsis ACS, ACO, ETR, CTR1, EIN2 and EIN3. We found that they are differentially regulated in different plant organs and in response to drought.