Genes and QTLs Controlling Heavy Metal Uptake in Perennial Grasses Grown on Phytotoxic Soil

Perennial grasses occupy diverse soils throughout the world, including many sites contaminated with heavy metals. Uncovering the genetic architecture of QTLs controlling mineral homoeostasis is critical for understanding the biochemical pathways that determine the elemental profiles of perennial plants. Breeders also seek to identify genes and QTLs to breed safe and nutritious forages on soils containing elevated concentrations of heavy metals.

A pseudo-backcross population derived from two perennial grass species, Leymus cinereus and L. triticoides, was clonally replicated and grown on phytotoxic and fertile soils. The concentrations of 17 minerals were analyzed over the course of three forage harvests.

Genome-wide QTL interval mapping and restricted multiple-QTL model scans detected a total of 23 QTLs for 16 of the 18 mineral traits. These QTLs were aligned to the genome sequence of barley (Hordeum vulgare) for comparison to candidate genes and other QTLs controlling heavy metal accumulation. Although three of four zinc QTLs were conserved across different test soils and aligned to zinc QTLs of barley, QTLs controlling arsenic, copper, lead, and other heavy metals did not correspond with other species and showed strong plant QTL – soil interactions. Two homoeologous molybdenum QTLs were closely associated with MOT1 orthogenes, which encode one of two known molybdate transporters in plants, and multiple possible candidate gene associations were identified for other heavy metals. Significant QTL variation and plant QTL – soil interactions demonstrated opportunities and pitfalls, respectively, to modify elemental profiles in perennial grasses through breeding.