Morphological, Histological, and Transcriptome Analysis of Doubled Haploid Plants in Poplars (<i>Populus simonii</i> × <i>Populus nigra</i>)

In this study, the poplar doubled haploid (DH) plants were used as the experimental material to explore the huge phenotypic differences between homozygous DH plants and the paternal plants, and the molecular regulation mechanism of the differential phenotypes. In this experiment, through morphological and histological observation and statistics, we found that the double haploid plants had significantly reduced plant height and ground diameter, increased leaf aspect ratio, premature senescence phenotype of top bud, and significant changes in the shape and cell area of the shoot apical meristem. Significantly differentially expressed genes were obtained using RNA-seq transcriptome sequencing. They were subjected to GO enrichment and KEGG analysis. Transcription factors with key functions were screened out for qRT-PCR to verify gene expression changes to predict gene function. The results showed that after the IAA and ABA treatment, the expression levels of some hormone-responsive genes in wild type plants were significantly changed with different treatment time. In the dihaploid plants, the corresponding genes also changed to different degrees, which reflected the changes in the response of the dihaploid plants to hormones. Compared to in WT, the differential expressed genes in the double haploids were involved in multiple physiological process such as response to oxidative stress, response to salicylic acid, plant pathogen interaction, and plant hormone signal transduction. A TF–centered gene regulatory network for phytohormone synthesis and plant senescence was constructed with the expression patterns of differentially expressed transcription factors (TFs). This study increases researchers’ understanding of the regulation of poplar growth and development and provides new research ideas for the creation of new species of poplar.