AemMPK6 from Aegilops markgrafii increases cadmium tolerance in transgenic Arabidopsis thaliana

Cadmium (Cd) is a common heavy metal pollutant that inhibits plant growth and development. Mitogen-activated protein kinase (MPK) plays a crucial role in plant responses to biotic and abiotic stresses. Here, an MPK gene referred to as mitogen-activated protein kinase 6 (AemMPK6) was isolated from Aegilops markgrafii (Greuter) Hammer and cloned to investigate the function in Cd stress response.

The study was conducted through yeast expression, transgenic verification, quantitative analysis and determination of physiological indexes to clarify the function of AemMPK6.

AemMPK6 expression was highly induced in roots and shoots of Ae. markgrafii under Cd stress. Overexpression of AemMPK6 significantly improved Cd tolerance in yeast. Phenotypic analysis showed that transgenic Arabidopsis thaliana exhibited higher growth compared to wild-type (WT) under Cd stress. The transgenic lines showed increased Cd accumulation in the roots and shoots, however, cadmium concentration in shoots was significantly lower than that in roots. The expression of genes involved in Cd transport and detoxification such as nicotinamide synthase 1 (AtNAS1) and yellow stripe-like protein 2 (AtYSL2) were increased in roots, but almost similar in shoots of transgenic lines compared with WT. The electrolyte leakage in the transgenic lines was lower than that in the WT. Besides, the levels of vacuolar processing enzyme (VPE) transcripts (AtαVPE) in transgenic lines were lower than those in the WT under Cd stress.

Our findings indicate that AemMPK6 confers Cd tolerance by regulating the expression of ion transport in the roots and inhibiting cell death-related genes to achieve Cd homeostasis.