Rice transcription factor, OsbHLH068, confers salinity stress tolerance

The basic/helix-loop-helix (bHLH) transcription factors (TFs) play important roles in the regulation of diverse developmental and physiological processes in plants. So far, at least 173 OsbHLH genes have been identified in rice. Though the expression levels of several OsbHLH genes were noticed to be up-regulated by salt treatments, such as OsbHLH068 gene; however, the gene functions of OsbHLH068 in salt-stress tolerance of rice are still unknown. In this study, the roles of OsbHLH068 and its Arabidopsis ortholog, AtbHLH112, were investigated under salt stress with reverse-genetics approaches. In Arabidopsis, under salt-treatment, the atbhlh112 mutant displays salt-intolerance and low leaf-temperature phenotypes. These physiological defects in atbhlh112 mutant could be complemented by heterologous expression of OsbHLH068 gene. In addition, heterologous over-expression of OsbHLH068 gene in Arabidopsis causes a post-germination developmental arrest (PGDA) phenotype, which refers to non-fully expanded cotyledon under salt treatment. Histochemical staining of promoter::GUS assay in transgenic Arabidopsis indicated that AtbHLH112 expressed in vascular tissue and trichome. Both OsbHLH068-GFP and GFP-OsbHLH068 fusion proteins are localized in the nucleus. Interestingly, compared with wide type (WT, Tainung67), the phenotypic analysis of over-expressed OsbHLH068 transgenic rice seedling showed increased salt crystals accumulation at the base of 1st leaf sheath under 250 mM NaCl treatment. Taken together, these results suggest that OsbHLH068 is a positive regulator that is involved in stress response of plant salt-stress tolerance.