The ASYMMETRIC LEAVES1 ortholog PagAS1a promotes xylem development and plant growth in Populus.

ASYMMETRIC LEAVES1 (AS1) is a central regulator of leaf polarity establishment in Arabidopsis. However, the functions of its ortholog genes in Populus are unclear. In this study, we performed gene expression analysis and found that the AS1 ortholog gene PagAS1a exhibited significantly higher expression levels in the secondary phloem than in the secondary xylem within the wood formation zone. Subcellular localization analysis showed that PagAS1a localizes in the nuclei. Compared to the wild type, both PagAS1a overexpression (PagAS1a-OE), and dominant repression (PagAS1a-SRDX) plants exhibited enhanced height and stem diameter growth. Analysis of stem cross-sections revealed that both overexpression and dominant repression of PagAS1 promoted secondary xylem development. We performed transcriptome sequencing (RNA-seq) for gene expression analysis, and identified 2,736 significantly differentially expressed genes (DEGs) in PagAS1a-OE plants. GO analysis revealed that genes associated with photosynthesis, lignin biosynthetic, and cellulose biosynthetic pathways were significantly enriched in up-regulated DEGs in PagAS1a-OE, while genes associated with lignin catabolic, and phenylpropanoid catabolic pathways were significantly enriched in down-regulated DEGs. Together, our results suggest that the AS1 ortholog PagAS1a is an important regulator of secondary xylem development and plant growth in Populus.