Genome-Wide Identification of the PLATZ Transcription Factor Family in Populus euphratica Oliv. and Functional Characterisation of PePLATZ8 in Drought Tolerance

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are a class of plant-specific transcription factors that have been identified and functionally characterised in multiple species. However, the PLATZ gene family has not yet been systematically characterised in Populus euphratica. In this study, 19 PePLATZ genes were identified and classified into five subgroups. The analyses of gene structure, conserved motifs and protein domains indicated that the PLATZ family is highly conserved during evolution. Meanwhile, promoter cis-acting element profiling suggested their potential roles in stress-responsive transcriptional regulation. Transcriptomic and qRT-PCR analyses showed that PePLATZ1, PePLATZ6, PePLATZ8, PePLATZ14 and PePLATZ19 were highly expressed in the roots, stems and leaves of P. euphratica and were strongly induced by drought stress. PePLATZ8 localised to the nucleus and lacked transactivation activity but acted as a transcriptional repressor in planta. Transgenic poplar lines overexpressing PePLATZ8 exhibited significantly enhanced drought tolerance. Furthermore, after drought treatment, PePLATZ8-overexpressing plants accumulated high levels of H2O2 and exhibited significantly increased total superoxide dismutase activity, which likely contributed to improved drought tolerance. Together, the above findings deepen our understanding of the structure–function relationships of PePLATZ proteins and identify PePLATZ8 as a promising candidate gene for the molecular breeding of drought-resistant poplar germplasm.