Comparative Abiotic Stress Tolerances of Saccharum MYB18 Orthologs in Stable Transgenic Tobacco Plants

Differentially expressed, stress-responsive, orthologs MYB transcription factors MYB18 were identified and isolated from sugarcane and its wild relative species. A genomic 1557 bp SoMYB18 was isolated from sugarcane var. Co740 encodes 1284 bp ORF while SsMYB18 1,470bp isolated from a wild relative Saccharum spontaneum gene encodes ORF of 1,074bp. SoMYB18 is a member of the R2R3-MYB subfamily, containing two MYB DNA-binding domains (R2, R3) and a SANT/MYB DNA-binding domain, In contrast SsMYB18 belongs to single repeat (R3) DNA binding domain family. These genes were transferred into tobacco, and stable transgenic plants expressing SoMYB18 and SsMYB18 were assessed for salt, drought and cold tolerance through biochemical estimations. In these transgenic lines, the activities of antioxidant enzymes (SOD, POD and CAT) were notably increased virtually to non-transformed ones. The MDA content was less and levels of chlorophyll and proline were also markedly high in both SoMYB18 and SsMYB18 overexpressing plants than that of non-transformed. Ectopic expression of SoMYB18 in tobacco conferred enhanced tolerance to salt stress, whereas overexpression of SsMYB18 exhibited appreciable tolerances to salt and cold. Single-repeat MYB transcription factor isolated from Saccharum spontaneum, SsMYB18 seems to be more promising candidate than the R2-R3-SoMYB18 gene as it is providing high level of tolerance to salt and cold stress and moderate to drought and has greater prospects in plant improvement provided that further studies at molecular level needs to be done.