Genome-wide identification of the oligopeptide transporter gene family in poplar and their responses to iron and cadmium.

BACKGROUNDS: The oligopeptide transporter (OPT) family belongs to a type of proton-coupled symporter and functions in the transport of metal ions, glutathione, phytochelatins (PCs), and metal-PC complexes, as well as in the regulation of metal homeostasis. Polplar, a fast-growing woody model species which has been resequenced multiple times, shows great potential in phytoremediation. However, the identification of OPT family genes and their responses to cadmium (Cd) and iron (Fe) remain poorly understood. RESULTS: This study identified 30 OPT genes (17 yellow stripe-like (YSL) subfamily members and 13 OPT subfamily members) in Populus trichocarpa, and most PtOPT proteins were localized to the plasma membrane and tonoplast. Twelve gene duplication events were detected among the members of the PtOPT gene family, with one duplication pair being a tandem duplication and the remaining 11 pairs being segmental duplications. Numerous cis-acting elements related to light responses, hormone responses, stress responses, and plant development have been identified. The expression profiles of the PtOPT genes varied significantly among different tissues. Coexpression networks centered on PtOPT4.2 were constructed to reveal its potential roles in cellular nitrogen compound metabolism, protein-containing complex metabolism, small molecule metabolism, and carboxylic acid metabolism. The expression levels of PtYSL6, PtYSL7.4, PtOPT2, PtOPT5.2, and PtYSL3.3 were highly induced by Cd under normal Fe conditions, whereas the expression levels of these five genes were reduced by Cd under high Fe conditions, indicating that these five genes may play roles in the transport and distribution of Fe and Cd, as well as in Cd detoxification. CONCLUSIONS: These findings enhance our understanding of the critical role of PtOPT genes in response to Fe and Cd, and provide valuable molecular targets for improving Cd phytoremediation potential.