Genome-wide investigation of malate dehydrogenase gene family in poplar (Populus trichocarpa) and their expression analysis under salt stress

Malate dehydrogenase (MDH) is widely distributed in plants and animals, and plays an important role in many metabolic processes. However, there have been few studies on MDH genes in poplar. In this study, 16 MDH gene sequences were identified from the Populus trichocarpa genome and renamed according to their chromosomal locations. Based on the phylogenetic analysis, the PtMDH genes were divided into five groups, and genes that grouped together all shared the same subcellular location and had similar sequence lengths, gene structures, and conserved motifs. Two pairs of tandem duplication events and three segmental duplication events involving five genes were identified from the 15 PtMDH genes located on the chromosomes. Each pair of genes had a Ka/Ks ratios < 1, indicating that the MDH gene family of P. trichocarpa was purified during evolution. Based on the transcriptome data of P. trichocarpa under salt stress and qRT-PCR verification, the expression patterns of PtMDH genes under salt stress were analyzed. The results showed that most of the genes were up-regulated under salt stress, indicating that they play a role in the response of poplar to salt stress. The PtMDH2 gene can be used as an important candidate gene to further explore the molecular mechanism of salt tolerance. This study lays the foundation for functional analysis of MDH genes and genetic improvement in poplar.