Molecular mechanism of leaf adaxial upward curling caused by suppression in .

Leaves are one of the vegetative organs of plants that are essential for plant growth and development. () gene is an indoleacetic acid (IAA) transporter that plays a critical role in leaf development. To determine the function of in leaf polarity formation in , the transgenic lines with overexpression (OE) and reduced expression (RE) were analyzed using the -mediated method. The RE lines displayed the characteristics of leaf margin adaxial upward curling, with lower expression of resulting in greater rolling. Tissue localization of IAA in the auxin reporter system proved that auxin in the RE was mainly distributed in the secondary veins, palisade tissues, and epidermal cells in the leaf margin area. The auxin content in the leaf margin area was significantly greater than that in the main vein tissue. The cell density of the palisade tissue and the ratio of palisade tissue to spongy tissue in the curled leaf margin of the RE lines were found to be significantly decreased. RNA-seq analysis revealed that the RE hormone-signaling pathway genes were significantly enriched compared with those of the OE and WT lines; in particular, the auxin response-related genes SAURs (i.e., , , , and ) and were found to be significantly upregulated. qRT-PCR analysis indicated that expression at the leaf margin was significantly lower than that near the main vein in the RE lines. In contrast, the expression levels of SAURs and were significantly higher than those near the midrib. In conclusion, regulates the expression of auxin response-related genes and the polar transport of auxin to change the polar form of the proximal and distal axes of birch leaves.