Abstract
Drought and salt stress are two important environmental factors that significantly restrict plant growth and production. Malate dehydrogenase is essential to life as it is engaged in numerous physiological processes in cells, particularly those related to abiotic stress reactions. However, a complete understanding on MDH family members in kenaf is not clear yet. In this study, subcellular localization analysis and a yeast transcriptional activation assay revealed that HcMDH1 was localized in chloroplasts but had no transcriptional activation activity. When exposed to salt or drought, yeast cells that express the HcMDH1 gene have a greater survival rate. Overexpression of HcMDH1 in Arabidopsisincreased seed germination rate and root growth when transgenic lines were exposed to varying concentrations of mannitol and NaCl. Subsequent physiological studies revealed that transgenic lines had higher concentrations of soluble carbohydrates, proline, and chlorophyll and lower concentrations of malondialdehyde (MDA) and reactive oxygen species (ROS). Furthermore, inhibiting HcMDH1 in kenaf using virus-induced gene silencing (VIGS) decreased salt and drought tolerance due to elevated ROS and MDA levels. In these silenced lines, the expression of six essential genes engaged in stress-resistance and photosynthesis, namely HcGAPDH, HcGLYK, HcFBA, HcFBPase, HcPGA, and HcLSD, is significantly altered under salt and drought stress. In summary, HcMDH1 is a positive regulator of salt and drought tolerance in kenaf, which may have implications for transgenic breeding.