Early transcriptional responses to mercury: a role for ethylene in mercury‐induced stress

Abstract

SummaryUnderstanding the cellular mechanisms of plant tolerance to mercury (Hg) is important for developing phytoremediation strategies of Hg-contaminated soils. The early responses of alfalfa (Medicago sativa) seedlings to Hg were studied using transcriptomics analysis.A Medicago truncatula microarray was hybridized with high-quality root RNA from M. sativa treated with 3 lM Hg for 3, 6 and 24 h. The transcriptional pattern data were complementary to the measurements of root growth inhibition, lipid peroxidation, hydrogen peroxide (H 2 O 2 ) accumulation and NADPH-oxidase activity as stress indexes.Of 559 differentially expressed genes (DEGs), 91% were up-regulated. The majority of DEGs were shared between the 3 and 6 h (60%) time points, including the 'stress', 'secondary metabolism' and 'hormone metabolism' functional categories. Genes from ethylene metabolism and signalling were highly represented, suggesting that this phytohormone may be relevant for metal perception and homeostasis.Ethylene-insensitive alfalfa seedlings preincubated with the ethylene signalling inhibitor 1-methylcyclopronene and Arabidopsis thaliana ein2-5 mutants confirmed that ethylene participates in the early perception of Hg stress. It modulates root growth inhibition, NADPH-oxidase activity and Hg-induced apoplastic H 2 O 2 accumulation. Therefore, ethylene signalling attenuation could be useful in future phytotechnological applications to ameliorate stress symptoms in Hg-polluted plants.

Role of Ethylene and Its Cross Talk with Other Signaling Molecules in Plant Responses to Heavy Metal Stress

“…The molecular mechanism of how plants can cope with different HM stresses varies from plant to plant, but in general, ethylene and its cross talk with other phytohormones or with signaling molecules are important for plant adaptation to HM-induced oxidative stress (Thapa et al, 2012;Montero-Palmero et al, 2014a, 2014b. It has been found that not only the production of ethylene but other phytohormones are also affected by excessive HM.…”

“…Other studies also suggested that an appropriate control of ethylene signaling could be used as a biotechnological approach to improve HM stress tolerance. In Arabidopsis, EIN2 gene function was found to be required for plant Al and Hg sensitivities, as root growth inhibition under HM stress was alleviated in all the Arabidopsis ein2-1, ein2-5, and etr1-3 single mutants (Sun et al, 2010;Montero-Palmero et al, 2014a). By contrast, the EIN2 gene was reported to be important for Pb resistance in Arabidopsis plants , suggesting that the role of ethylene in plant responses to HM stress is complex and, perhaps, depends on the types of HMs to which the plants are exposed.…”

“…Ethylene and hydrogen peroxide were believed to act in a synergistic manner in tomato, and hydrogen peroxide plays an important role in ethylene-related Cd-induced cell death (Liu et al, 2008). Several studies have shown that HMs, such as Cd, Cu, Fe, Zn, Hg, manganese, and Al, can induce ROS production and alter the activities of antioxidant enzymes, including catalase, superoxide dismutase (SOD), peroxidase, ascorbate peroxidase (APX), and glutathione reductase (GR), in plants (Sun et al, 2010;Yuan et al, 2013;Montero-Palmero et al, 2014a;Khan et al, 2015b;Mostofa et al, 2015b). It was found that the application of ethephon or NBD could somehow adjust the stress-induced ethylene, thereby alleviating photosynthetic inhibition and decreasing oxidative stress, perhaps by the enhancement of SOD, APX, and GR metabolism, in mustard plants treated with Ni and Zn .…”

Cross Talk between Nitric Oxide and Phytohormones Regulate Plant Development during Abiotic Stresses

“…It is well documented that exposure to HMs enhances the production of ET [59] due to increased 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) activity in metal stressed plants [60]. Cross talk between ET and stress signaling molecules like NO is important to understand the mechanisms of plant adaptation to HM-induced oxidative stress [61][62][63]. More recently, Thao et al [51] suggested a possible link between NO and ET through MAPKs in plants exposed to HM stress.…”

Possible reasons for tolerance to mercury of Lupinus albus cv. G1 inoculated with Hg-resistant and sensitive Bradyrhizobium canariense strains

“…However, up to now, little is known about the adverse effects of Hg on the cellular structure of lupin leaves and nodules or on their function. These studies are necessary for better understanding of the cellular mechanisms of plant tolerance to Hg, which is important for developing phytoremediation strategies of Hg-contaminated soils and environments (Montero-Palomero et al 2014).…”