A seed-specific DNA-binding with One Finger transcription factor, RPBF, positively regulates galactinol synthase to maintain seed vigour in rice

Seed vigour and longevity are intricate yet indispensable physiological traits for agricultural crops, as they play a crucial role in facilitating the successful emergence of seedlings and exert a substantial influence on crop productivity. Transcriptional regulation plays an important role in seed development, maturation, and desiccation tolerance, which are important attributes for seed vigour and longevity. Here, we have investigated the regulatory role of the seed-specific DNA binding with the One Finger (DOF) transcription factor and the RPBF (Rice P-box Binding Factor) in seed vigour. RPBF modulates the transcription of galactinol synthase and improves seed vigour. The promoter region of Galactinol synthase (GolS)-encoding genes from different species was enriched with DOF binding sites, and the expression levels of both RPBF and OsGolS were found to enhance during seed development. Furthermore, direct interaction of RPBF with OsGolS promoter has been demonstrated through multiple approaches: yeast one-hybrid (Y1H) assays, in planta promoter-GUS assays, dual luciferase assay, and in silico molecular docking. To assess functionality, Agrobacterium-mediated genetic transformation of rice was performed to generate the RNAi lines with reduced RPBF expression. In these RNAi lines, a reduction in both galactinol and raffinose content was observed. Since galactinol and raffinose are known contributors to seed vigour, the T2-transgenic lines were assessed for vigour and viability. For this, RNAi seeds were subjected to accelerated ageing by exposing them to high relative humidity and temperature, followed by scoring the germination and viability potential. Tetrazolium and seed germination assay revealed that the RNAi seeds were more sensitive to ageing compared to their wild-type and vector control counterparts. Collectively, this is the first report demonstrating that the DOF transcription factor RPBF controls the seed vigour through transcriptional regulation of galactinol synthase.