Transcriptome Analysis of Developing Xylem Provides New Insights into Shade Response in Three Poplar Hybrids

Poplars have a strong response to light, and shade is one of the main environmental factors that limits the growth and development of poplars. Exploring the response mechanism of the developing xylem of poplar under shady conditions is of great reference significance for improving wood yields. In this study, three excellent hybrids of poplar (Populus euramericana 'Zhonglin46' (Pe), Populus deltoides '27-17' (Pd), Populus x 'Wq156' (Pw) were studied under shady conditions. Based on the phenotypic data and developing a xylem transcriptome analysis, the molecular mechanism of poplars' response to shade was preliminarily revealed, and the core regulatory genes responding to shade were identified by a weighted co-expression network analysis (WGCNA). The results showed that Pw growth was significantly affected by shade, while Pe growth was slightly affected by shade. An enrichment analysis of 13,675 differentially expressed genes (DEGs) found that shade affected the expression of genes related to the glutathione metabolic pathway. The WGCNA analysis identified two modules ("Brown" and "Purple") related to the shade response and discovered seven hub genes. These hub genes were related to xylem development, vascular cambium division, stomatal development, and phytochrome A signal transduction. These results provide important basic information for gaining insight into the molecular response to shade in different poplar hybrids.