Clonal mosaic analysis of EMPTY PERICARP2 reveals nonredundant functions of the duplicated HEAT SHOCK FACTOR BINDING PROTEINs during maize shoot development.

The paralogous maize proteins EMPTY PERICARP2 (EMP2) and HEAT SHOCK FACTOR BINDING PROTEIN2 (HSBP2) each contain a single recognizable motif: the coiled-coil domain. EMP2 and HSBP2 accumulate differentially during maize development and heat stress. Previous analyses revealed that EMP2 is required for regulation of heat shock protein (hsp) gene expression and also for embryo morphogenesis. Developmentally abnormal emp2 mutant embryos are aborted during early embryogenesis. To analyze EMP2 function during postembryonic stages, plants mosaic for sectors of emp2 mutant tissue were constructed. Clonal sectors of emp2 mutant tissue revealed multiple defects during maize vegetative shoot development, but these sector phenotypes are not correlated with aberrant hsp gene regulation. Furthermore, equivalent phenotypes are observed in emp2 sectored plants grown under heat stress and nonstress conditions. Thus, the function of EMP2 during regulation of the heat stress response can be separated from its role in plant development. The discovery of emp2 mutant phenotypes in postembryonic shoots reveals that the duplicate genes emp2 and hsbp2 encode nonredundant functions throughout maize development. Distinct developmental phenotypes correlated with the developmental timing, position, and tissue layer of emp2 mutant sectors, suggesting that EMP2 has evolved diverse developmental functions in the maize shoot.