Physiological and DNA methylation analysis provides epigenetic insights into chromium tolerance in kenaf

Abstract

As a toxic heavy metal, chromium (Cr) has become a major environmental concern in cultivated areas. Kenaf is a fast-growing fibre crop with high economic value and can potentially be used for phytoremediation. However, limited information is known regarding the mechanism of kenaf in response to Cr stress, especially from the perspective of epigenetics. The present study was conducted to explore the physiological and DNA methylation changes in kenaf seedlings grown under different concentrations (from 0 to 600 μM) of Cr stress. The results show that Cr reduced plant height, root length, biomass, and root cell viability compared with the control. The activities of antioxidant enzymes (SOD, POD, and CAT) increased under Cr stress and reached their peaks at Cr concentrations of 500, 300, and 400 μM respectively. Methylation-sensitive amplification polymorphism (MSAP) analysis revealed a significant positive correlation between an increase in the total DNA methylation level and Cr concentration, and the increasing rate ranged from 20.97% to 26.34%. Among the 205 loci examined, 40 differentially methylated DNA fragments (DMFs) were cloned and analysed. DMFs such as the ABC transport family (ABC) may play essential roles in kenaf Cr stress. In addition, the methylation status of three Cr stress- related DMFs (HcABC, HcRHP and HcTyDC) was investigated via the bisulfite sequencing polymerase chain reaction (BSP) method. Furthermore, knockdown of HcTyDC by virus-induced gene silencing (VIGS) led to increased sensitivity to Cr stress. Overall, our data indicate that higher antioxidant activity and increased cytosine methylation levels in the plant genome could be related to Cr tolerance mechanisms in kenaf, and these changes then affect the expression of specific genes involved in the Cr stress response.