OP 4 . 1 The involvement of protein kinase A in humoral immune response of Galleria mellonella

The major challenges which plants have to withstand is osmotic stress (caused by drought, high and low temperature and high salinity), and wounding (caused by mechanical damage, f. ex. wind or herbivorous). Plant cells respond to these abiotic stresses by a multi-component defense strategy. Several families of protein kinases are involved in plant stress signaling. Among them are members of mitogen activated protein kinase (MAPK), calcium-dependent protein kinase (CDPK), GSK3, and SNF-1-related kinase (SnRK). In our laboratory we have identified and cloned protein kinase rapidly activated in Nicotiana tabacum BY-2 cells subjected to osmotic stress. The tobacco kinase named Osmotic Stress Activated Kinase (NtOSAK) was classified to the SnRK2 family. The activity of the enzyme correlates with phosphorylation of two serine residues in the kinase activation loop, indicating that this phosphorylation can be responsible for the enzyme activation in response to osmotic stress. Using protein sequence data obtained from a calcium phospholipids-regulated protein kinase purified from maize (Zea mays), we isolated a cDNA encoding a maize calcium-dependent protein kinase (CDPK), designated ZmCPK11. Escherichia coli-expressed, GST-ZmCPK11 was catalytically active in a calcium-dependent manner, and activated by phospholipids. In maize leaves the activity and the expression of ZmCPK11 was regulated by wounding. The level of ZmCPK11 transcript is also increased in non-injured neighboring leaves, what suggests that the maize protein kinase is involved in a systemic response to wounding.