Regulated promoters applied to plant engineering: an insight over promising soybean promoters under biotic stress and their cis-elements

Abstract

Promoters are upstream gene regulatory sequences recognized by transcription factors (TFs) involved in controlling transcription initiation and progression. For modern crop improvement, the design of efficient gene constructs relies on promoter efficiency, tissue specificity, and other characteristics that allow the introgression of agronomically relevant traits to overcome biotic and abiotic stresses. Several constitutive viral promoters, such as pCaMV35S, remain widely employed in the transgenic plant generation, but their indiscriminate use leads to gene silencing triggering and metabolic penalties impacting plant fitness. The identification and functional characterization of plant-derived promoters can unveil alternatives to commonly used non-homologous promoters; however, knowledge over them remains limited, especially for crops. This review summarizes plant promoters used to drive foreign gene expression in homologous and heterologous systems, focusing on inducible soybean promoters from genes upregulated by different biotic stresses. Analyses of these soybean promoters revealed 22 coincident cis-acting elements that can be used for synthetic engineering promoters responsive to multiple biotic stresses and, therefore, efficiently drive gene expression, conferring desirable traits in transgenic soybean. In addition, we also revisited commercial and protected promoters to provide an update on soybean promoters and gain new insights into superior crops’ development.