Transcriptional regulation is involved in responding to cadmium (Cd) stress in plants. However, the molecular mechanisms of Cd stress responses regulated by transcription factors remain largely unknown in plants. In this study, a rice (Oryza sativa) NAC (no apical meristem [NAM]; Arabidopsis transcription activation factor [ATAF]; cup-shaped cotyledon [CUC]-related) family transcription factor, OsNAC300, was isolated and functionally characterized for its involvement in Cd stress responses and tolerance. OsNAC300 was localized to the nucleus. OsNAC300 was mainly expressed in roots and significantly induced by Cd treatment. Knockout of OsNAC300 resulted in increased sensitivity to Cd stress, while its overexpression lines enhanced tolerance to Cd stress. RNA-Seq analysis revealed that the mutant is impaired in regulating some important genes that were responsive to Cd stress in wild-type rice, such as the pathogenesis-related genes 10a (OsPR10a), OsPR10b, chalcone synthase 1 (OsCHS1), and several others, which was validated by reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis. Moreover, chromatin immunoprecipitation-qPCR assays and luciferase reporter assays demonstrated that OsNAC300 directly binds to the promoters of OsPR10a, OsPR10b, and OsCHS1 and activates their transcription. Overall, OsNAC300 is an important regulatory factor in Cd stress responses and tolerance in rice.

Zinc deficiency is the most prevalent micronutrient disorder in rice and leads to delayed development and decreased yield. Nevertheless, despite its primary importance, how rice responds to zinc deficiency remains poorly understood. Herein, we present genetic evidence that OsbZIP48 is essential for regulating rice responses to zinc deficiency. Using the reverse genetics approach, genetic inactivation of OsbZIP48 in rice seedlings caused a hyper sensitivity to zinc deficiency, associated with a significant decrease in the root-to-shoot translocation of zinc. Consistently, OsbZIP48 was constitutively expressed in roots, slightly induced by zinc deficiency in shoots, and localized into nuclei induced by Zn deficiency. Comparative transcriptome analysis of the wild-type plants and osbzip48 mutant grown under zinc deficiency enabled the identification of OsbZIP48 target genes, including key zinc transporter genes (OsZIP4 and OsZIP8). We demonstrated that OsbZIP48 controlled the expressions of these genes by directly binding to their promoters, specifically to the zinc deficiency response element (ZDRE) motif. Collectively, we showed that the OsbZIP48 gene encodes for a transcription factor in rice, and demonstrates its critical role in the response to zinc deficiency in this crop. This knowledge is crucial for the design of rice plants that are resilient to the globally prevalent zinc limitation through zinc bio-fortification programs.