Translation initiation factors are differentially regulated in cereals during development and following heat shock

The level of protein synthetic activity varies greatly in plants during development or following many environmental stresses. In order to determine whether these global changes in protein synthesis involve changes in the expression of the translational machinery itself, the expression patterns of the initiation factors (elFs) during cereal seed development, germination, and in leaves following a heat shock were investigated. The expression patterns of initiation factors during seed development fell into four classes: those whose levels were high during early to mid-development but decreased during late seed development (elF4 A, elFiso4E, elFiso4G, and most elF3 subunits); those whose levels increased from early to mid-development followed by a decrease during late seed development (elF4B, elF4E, elF2 alpha, elF2 beta, and PABP); those whose levels steadily increased throughout seed development (elF4G); and those whose levels remained constant (the p34 subunit of elF3). In contrast to these observations, the expression patterns of the factors appeared to be coordinately regulated during early germination although differences were observed at later stages. Following a heat shock, the changes in initiation factor expression in wheat leaves fell into two classes, those whose level increased (elF4G, elFiso4G, elF3, and PABP) and those whose level remained unchanged (elF4 A, elF4B, elF4E, elFiso4E). These observations reveal the complexity of the expression patterns of the initiation factors during seed development, germination, and following thermal stress and may have mechanistic importance for the selective translation of certain mRNAs under these conditions.