Genome-wide identification of PLATZ genes related to cadmium tolerance in Populus trichocarpa and characterization of the role of PtPLATZ3 in phytoremediation of cadmium

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are a class of plant-specific zinc finger transcription factors that perform critical functions in plant development and resistance. However, the function of PLATZs in heavy metal tolerance has not yet been investigated. Moreover, only a few PLATZ proteins have been functionally characterized in tree species. In this study, we identified 18 PtPLATZ genes in Populus trichocarpa, an important woody model plant, and classified them into five groups. PtPLATZ genes attributed to the same clade usually possess similar exon-intron structures containing two or three introns, as well as a similar motif composition. Furthermore, chromosomal location analysis indicated an uneven distribution of PtPLATZ genes on 13 of the 19 Populus chromosomes. Promoter cis-acting element prediction and gene expression analysis showed that PtPLATZ genes were highly responsive to heavy metal stress. Heterologous yeast expression revealed that PtPLATZ1, PtPLATZ2, PtPLATZ3, PtPLATZ4, PtPLATZ8 and PtPLATZ9 are significantly involved in Cd tolerance. In addition, transgenic expression of PtPLATZ3 significantly enhanced Cd tolerance and accumulation, slowed the decline in chlorophyll content, maintained membrane integrity in Populus, and increased the expression of genes related to Cd tolerance and accumulation. In conclusion, our results suggest the potential of PtPLATZ3 to improve Cd tolerance and accumulation in Populus, which is of great significance for phytoremediation.