Overexpression of an alfalfa (Medicago sativa) gene, MsDUF, negatively impacted seed germination and response to osmotic stress in transgenic tobacco

Many stress-responsive genes have been identified in alfalfa (Medicago sativa L.). The function of these genes, however, are mostly not understood. We reported previously a novel stress-responsive gene, MsDUF, from alfalfa that was up-regulated under drought stress. In the present study, we examined its function by overexpressing the gene in Nicotiana tabacum. We found that overexpression of MsDUF reduced seed vigor and germination percentage under normal conditions or osmotic stress. The reduced seed vigor and germination was associated with an increased ABA content in the overexpressor seeds. Further analysis revealed that overexpression of MsDUF resulted in up-regulation of transcript levels of ABA biosynthesis genes (ZEP, NCED1 and NCED6) in the seeds. Compared with wild type, MsDUF-overexpression seedlings displayed significantly lower chlorophyll content and reduced soluble sugar content under normal conditions. MDA content was significantly higher in MsDUF-overexpressors compared to wild type under ABA treatment, while soluble sugar content and peroxidase activities were significantly lower in MsDUF-overexpressors. Our results suggest that MsDUF may act as a negative regulator in controlling seed vigor and responses to osmotic stress in plants.