Brassinosteroid application affects the growth and gravitropic response of maize by regulating gene expression in the roots, shoots and leaves

Brassinosteroids (BRs) are a class of plant-specific steroid hormones that play key roles in plant physiology and that actively participate in the regulation of plant responses to stress. Thus, these compounds are also considered biostimulants that could be applied to crops to improve plant performance and induce abiotic stress tolerance. In this study, with a combined physiological and molecular approach, new insights into the effects of 24-epibrassinolide (EBL), a synthetic BR, on hydroponically grown maize seedlings were gained. To this aim, a preliminary assessment of the effect of different EBL concentrations and treatment times on root elongation was evaluated to determine the concentration to use in subsequent experiments. Treatment with 1 nM EBL and an exposure time of 48 h were selected to better assess the effects of this molecule on shoot growth and the root gravitropic response. Subsequently, an untargeted RNA-Seq-based approach was applied to obtain an overview of the transcriptomic regulation occurring in the roots, shoots and leaves upon exogenous brassinosteroid application. Our outcomes highlight the substantial influence exerted by this molecule on the growth and root gravitropic response of maize seedlings. Moreover, new insights into the BR response and BR signalling in plants were gained by performing the functional characterization of differentially expressed genes via Gene Ontology (GO) and pathway analyses. Overall, this study provides useful information that could help future agricultural applications of these substances.