Upregulated expression of MYB4, DREB1 and AP37 transcription factors modulates cold stress response in high-altitude...

Cold stress is an upcoming challenge for rice (Oryza sativa L.) cultivation, especially at the seedling establishment stage. It causes serious constraints in its production and productivity as it is a thermophilic cereal crop. North-western Himalayan region has a rich repository of temperate rice genotypes, and there is a need to identify cold-tolerant rice varieties from these available genetic resources.

The present study screened 90 rice accessions (indica and japonica) grown in the high-altitude regions at 2200 m amsl for cold tolerance (5 °C) at the seedling stage, and found 14 highly cold-tolerant accessions. Almost eighty per cent of the indica types clustered into cold-sensitive class. One cold-tolerant japonica (GS-74) accession and one cold-susceptible (SR-4) accession were used to compare their biochemical and gene expression response during cold stress and after recovery. A wide range of differences was noticed at different time points in the accumulation of ROS scavengers, osmo-protectants and antioxidant enzymes, with significant differences between the contrasting genotypes. Similarly, gene expression of five transcription factors OsMYB4, OsAP37, OsDREB1A, OsDREB1B and OsDREB1D revealed their role in cold responsiveness at the seedling stage, critically modulating the cold-induced osmoprotectant-mediated tolerance mechanism.

This is the first study that explored the high-altitude Himalayan rice germplasm for cold tolerance at the critical S3 seedling stage under controlled conditions. It demonstrated that the upregulation of OsDREB1A, OsDREB1B, OsMYB4 and OsAP37 transcription factors modulates cold stress response in rice via a complex mechanism involving ROS scavengers and osmoprotectants.