Genetic control and molecular responses of Medicago truncatula to cadmium stress

Cadmium (Cd) is a non-essential metal highly toxic to plants, animals, and humans. To understand the heritability of Cd tolerance in Medicago truncatula, a QTL analysis was performed using a population of 147 recombinant inbred lines (RILs) in the F8 generation at seedling stage. The RILs and parental lines were grown for 6 days under exposure to ± 15 µM Cd on water agar. Length, diameter, fresh weight, and dry weight of root, as well as fresh weight and dry weight of aerial parts, were measured. Quantitative trait loci (QTL) analysis was performed with the parameters root length and fresh leaf weight using simple and composite interval mapping. Cd significantly decreased root length. One QTL for Cd response was mapped to chromosome 8 with root length which explained 9.35% of the phenotypic variance. Another QTL was identified for fresh leaf weight under Cd stress on chromosome 7. Genotype effect was highly significant for fresh leaf weight, fresh root weight, and dry leaf weight. Ten among the most susceptible and the most tolerant lines were pooled respectively to analyze the expression of genes encoding glutathione reductase (GR), glutathione S-transferase (GST), superoxide dismutase (SOD), peroxidase (PRX), and M. truncatula MonoSaccharide Transporter1. Expression of GR, GST, MST1, PRX, and SOD was upregulated after 24 h in the susceptible pool, then returned to basic levels. Expression of GR, GST, and PRX in the tolerant pool was upregulated after 96 h only, while MST1 and SOD exhibited no change at any time.