Abstract
Understanding genetic variation for the response of Populus to heavy metals like cadmium (Cd) is an important step in elucidating
the underlying mechanisms of tolerance. In this study, a pseudo-backcross pedigree of Populus trichocarpa Torr. &
Gray and Populus deltoides Bart. was characterized for growth and performance traits after Cd exposure. A total of 16 quantitative
trait loci (QTL) at logarithm of odds (LOD) ratio ≥ 2.5 were detected for total dry weight, its components and root
volume. Major QTL for Cd responses were mapped to two different linkage groups and the relative allelic effects were in
opposing directions on the two chromosomes, suggesting differential mechanisms at these two loci. The phenotypic variance
explained by Cd QTL ranged from 5.9 to 11.6% and averaged 8.2% across all QTL. A whole-genome microarray study led to
the identification of nine Cd-responsive genes from these QTL. Promising candidates for Cd tolerance include an NHL repeat
membrane-spanning protein, a metal transporter and a putative transcription factor. Additional candidates in the QTL intervals
include a putative homolog of a glutamate cysteine ligase, and a glutathione-S-transferase. Functional characterization
of these candidate genes should enhance our understanding of Cd metabolism and transport and phytoremediation capabilities
of Populus.
