BACKGROUND: ERECTA (ER) is a leucine-rich repeat-receptor-like kinase gene (LRR-RLK) encoding a protein isolated from Arabidopsis. Although the regulatory functions of ER genes have been widely explored in plant development and disease resistance, their roles in drought stress responses remain to be clarified.RESULTS: In this study, we cloned and characterized two ER genes, SbER1-1 and SbER2-1, from the drought-tolerant model plant sorghum (Sorghum bicolor L.). Under drought stress, the two genes were expressed in the leaves and stems but not in the roots, and SbER2-1 transcript accumulation in the stem was increased. SbER2-1 was localized both on the plasma membrane and in the chloroplast. Moreover, SbER2-1 expression in Arabidopsis and maize conferred increased drought tolerance, especially in regard to water-use efficiency, increasing the net photosynthetic rate in maize under drought stress. Based on RNA-Seq analysis together with the physiological data, we conclude that the transgenic maize plants have upregulated phenylpropanoid metabolism and increased lignin accumulation under drought stress.CONCLUSIONS: Our results demonstrate that SbER2-1 plays an important role in response to drought stress. Furthermore, photosynthetic systems and phenylpropanoid metabolism are implicated in SbER2-1-mediated drought stress tolerance mechanisms. The use of genetic engineering to regulate SbER2-1 expression in plants and to breed new varieties tolerant to drought is a research field full of potential.