Role of GCN2 in Maize Cold Response

Wild type maize is deficient in several key amino acids necessary for proper human nutrition. The maize opaque2 mutation gives the grain a more complete protein content, but it makes the endosperm fragile. Lines known as Quality Protein Maize (QPM) have been created to combine enhanced protein content with stronger endosperm, but they are difficult to produce because they require the introgression of several opaque2 modifier genes. A better understanding of the mechanisms that control the opaque2 gene could help in the improvement of QPM. Translation of opaque2 is regulated by the protein kinase GCN2, which is activated by low amino acid levels. GCN2 activity has also been implicated in other environmental stresses, such as drought and extreme temperatures. This study aims to examine the relationship between GCN2 and the CBL/CIPK stress response pathway. Stress responses in plants often induce specific increases in cytosolic calcium levels, which are decoded by CBLs. CBLs signal forward to specific CIPKs, which enact stress response. This study analyzed expression of CBL4, CIPK16, CIPK17, and CIPK24 under conditions of cold stress in wild type and GCN2 mutant seedlings. Maize seedlings were grown in cold chambers, and leaf tissue samples were collected at several time points. GCN2 mutant plants thrived more effectively than wild type plants under cold conditions. Additionally, RNA was extracted from samples and used to synthesize cDNA. Expression of cold response genes was evaluated using qPCR. Expression of all cold response genes was increased in GCN2 mutant seedlings as compared to wild type seedlings grown at cold temperatures. This is indicative of a link between GCN2 activity and maize cold response.