OsABAR1, a novel GRAM domain-containing protein, confers drought and salt tolerance via an ABA-dependent pathway in rice

Abstract

Glucosyltransferases-like GTPase activators and Myotubularin (GRAM) domain-containing proteins are important for plant development and responses to biotic stresses. However, the effects of GRAM proteins on abiotic stress responses remain unclear. In this study, we identified a novel GRAM protein-encoding gene, OsABAR1, and characterized its regulatory functions related to rice drought and salt tolerance. The OsABAR1 protein was localized in the cytoplasm and nucleus. Among all examined organs, the OsABAR1 transcript level was highest in the roots. Moreover, OsABAR1 expression was up-regulated by drought and salinity stresses. The OsABAR1-overexpressing (OsABAR1-OX) lines exhibited enhanced tolerance to drought and salinity, whereas the knock-out lines (Osabar1) had the opposite phenotypes. We further analyzed the involvement of OsABAR1 in the abscisic acid (ABA) signaling pathway. The OsABAR1 expression level was up-regulated by ABA. In turn, OsABAR1 regulated the expression of ABA metabolic genes and responsive genes. Furthermore, OsABAR1-OX seedlings were hypersensitive to exogenous ABA, whereas Osabar1 seedlings were hyposensitive. These results imply that OsABAR1 is a positive regulator of the ABA pathway and confirm that OsABAR1 improves rice drought and salt tolerance via an ABA-dependent pathway. This study is the first to clarify the regulatory roles of GRAM proteins in rice responses to abiotic stresses.