The SPL transcription factor TaSPL6 negatively regulates drought stress response in wheat

Environmental stresses, such as heat and drought, severely affect plant growth and development, and reduce wheat yield and quality globally. Squamosa promoter binding protein-like (SPL) proteins are plant-specific transcription factors that play a critical role in regulating plant responses to diverse stresses. In this study, we cloned and characterized TaSPL6, a wheat orthologous gene of rice OsSPL6. Three TaSPL6 homoeologs are located on the long arms of chromosomes 4A, 5B, and 5D, respectively, and share more than 98% sequence identity with each other. The TaSPL6 genes were preferentially expressed in roots, and their expression levels were downregulated in wheat seedlings subjected to heat, dehydration, and abscisic acid treatments. Subcellular localization experiments showed that TaSPL6 was localized in the nucleus. Overexpression of TaSPL6-A in wheat resulted in enhanced sensitivity to drought stress. The transgenic lines exhibited higher leaf water loss, malondialdehyde and reactive oxygen species (ROS) content, and lower antioxidant enzyme activities after drought treatment than wild-type plants. Gene silencing of TaSPL6 enhanced the drought tolerance of wheat, as reflected by better growth status. Additionally, RNA-seq and qRT-PCR analyses revealed that TaSPL6-A functions by decreasing the expression of a number of genes involved in stress responses. These findings suggest that TaSPL6 acts as a negative regulator of drought stress responses in plants, which may have major implications for understanding and enhancing crop tolerance to environmental stresses.