Cytological and transcriptional analysis reveal phosphatidylinositol signaling pathway plays key role in mitotic division of Pyropia yezoensis

The phosphatidylinositol (PI) signaling system, a central regulator of eukaryotic metabolism, is widely found in eukaryotes for regulating a variety of cell activities. Most of the genes in the PI signaling system were found conserved in Pyropia yezoensis . In this experiment, wortmannin was used as an inhibitor to inhibit the activity of phosphatidylinositol-3 kinase ( PI3K ), an important regulator of the PI signaling system. After wortmannin treatment, the mitotic division of P. yezoensis was significantly inhibited in a dose-dependent manner, and the mitotic division percentage was reduced by 68.1% and 91.9% in the 5- and 10-µmol/L groups, respectively. When thalli were treated with wortmannin, the levels of reactive oxygen species (ROS) were significantly decreased. Furthermore, the expression level of PI3K was inhibited and the expression levels of downstream genes regulated by PI3K was significantly changed. In the PI3K-AGC signaling pathway, the expression levels of Serine/threonine protein kinase ( AGC ) and cyclin-dependent kinases A ( CDKA ) were downregulated, while WEE1 kinase gene ( WEE1 ) was upregulated. Three nicotinamide adenine dinucleotide phosphate (NADPH) oxidase genes were downregulated after wortmannin treatment. These results indicate that the PI signaling system plays an important role in the regulation of cell activity in P. yezoensis . It was speculated that the growth and development of P. yezoensis might be regulated by P. yezoensis PI3K , which promoted the expression of the AGC gene and further regulates the expression of downstream WEE1 and CDKA genes to advance mitotic division, and also promoted the expression level of NADPH oxidase that regulates ROS homeostasis.