Pearl millet stress-responsive NAC transcription factor PgNAC21 enhances salinity stress tolerance in Arabidopsis

Pearl millet (Pennisetum glaucum) is the sixth-leading cereal crop and a staple food crop. It is known for its high tolerance to abiotic stress and good nutrient profile. NAC (NAM, ATAF1/2 and CUC) transcription factors (TFs) play an important role in abiotic stress tolerance. In our study, the pearl millet stress-responsive NAC TF gene PgNAC21 was characterized. Gene expression analysis revealed that PgNAC21 expression is induced by salinity stress and abscisic acid (ABA) treatment. In silico promoter analysis showed the presence of ABA response elements (ABREs) and MYB TF binding sites. A yeast one-hybrid assay indicated that a putative MYB TF in pearl millet, PgMYB1, binds to the promoter of PgNAC21. A transactivation assay in yeast cells revealed that PgNAC21 functions as a transcription activator and that its activation domain is located in its C-terminus. Relative to control plants, Arabidopsis plants overexpressing PgNAC21 exhibited better seed germination, heavier fresh weight and greater root length under salinity stress. Overexpression of PgNAC21 in Arabidopsis plants also enhanced the expression of stress-responsive genes such as GSTF6 (GLUTATHIONE S-TRANSFERASE 6), COR47 (COLD-REGULATED 47) and RD20 (RESPONSIVE TO DEHYDRATION 20). Our data demonstrate that PgNAC21 functions as a stress-responsive NAC TF and can be utilized in transgenic approaches for developing salinity stress tolerance in crop plants.