| Summary: | Polyploids exhibit different phenotypes compared to those of diploids in plants, and the important role of polyploids in tree breeding has been widely recognized. The transcriptomes detected by RNA-seq in the <i>Populus</i> triploid by doubling the chromosomes of the female gamete, in the triploid by doubling the chromosomes of somatic cells and the diploid with the parent were compared to reveal the patterns of gene expression of tetraploid leaves and their influence on growth. The results showed that the high expression of <i>GATA</i> and <i>PORA</i> in tetraploid leaves was the reason for the higher chlorophyll content in the leaves than in diploid and triploid leaves. The 11-day-old tetraploid leaves began to enter the aging stage. Compared with that in the diploid, <i>GRF</i> was significantly upregulated, while the amylase genes were downregulated. Compared with those in the triploid, 3 <i>STN7</i> genes that regulate photosynthetic genes and <i>PGSIP</i> genes which are related to starch synthesis, were significantly downregulated in the tetraploid, and the auxin receptor protein <i>TIR1</i> was also significantly downregulated. In the tetraploid, auxin-regulating genes such as <i>GH3</i> and <i>AUX/IAA</i> as well as genes involved in the regulation of leaf senescence, <i>SAG</i> genes and <i>SRG</i> genes were significantly up-regulated, resulting in a decrease in the auxin content. In senescent leaves, <i>CHLD</i>, <i>CHLI1,</i> and <i>CHLM</i> in the early stage of chlorophyll synthesis all began to downregulate their expressions, leading to the downregulation of <i>LHC</i> genes and a decrease in their photosynthetic efficiency, which led to the downregulation of carbon fixation-related genes such as <i>SS</i> genes, thus affecting carbon synthesis and fixation. This finally led to the slow growth of tetraploid plants. These data represent the transcriptome characteristics of tetraploid, and they can be used as a resource for further research on polyploids and provide a reference for further understanding of the function of polyploid vegetative growth-related genes.
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