The Molecular Mechalism Of Cd-induced Ethylene Production And Its Role In Cd Response In Arabidopsis

It has been reported that Cd exposure induced large amount of ethylene accumulation in Arabidopsis. However, the possible molecular mechanisms leading to the production of ethylene and the effect of Cd induced production of ethylene is still unclear. In the current study, we found that Cd exposure induced ethylene accumulation within 1 hour, exogenous ACC (Ethylene precursor) at 10 μM greatly increased the amount of root Cd content, thus exacerbating Cd stress-induced root elongation inhibit. Confirming with this, the ethylene-insensive mutants accumulated less Cd content in root and shoot and alleviate Cd stress-induced elongation inhibit and chlorosis. Cd exposure up-regulated the expression of AtACS2 and AtACS6, key genes related to the biosynthesis of ethylene, and the ethylene induction under Cd stress in acs2acs6 mutant is rather low. MPK6 is demonstrated to be involved in the transcriptional and post-translational activation of ACS2 and ACS6 and the reduced ethylene level under Cd stress in mpk6 mutant in turn suppressed the Cd accumulation, which finally resulted in significant Cd resistance in mpk6 mutant. Furthermore, the up regulation of NAS1, NAS2, IRT2, IREG2 and MTP3, gene related to the sequestration of cadmium in root cells, is reduced in mpk6 and ethylene-insensitive mutant, leading to the less cadmium accumulation in root of these mutants. Taken together, our data support that MPK6 and ACS2, ACS6 are involved in Cd stress-induced ethylene production, and ethylene can further exacerbate Cd toxicity.