The Post-Germinative Role of the Maize Gene Emp4

The maize empty pericarp4 (emp4) gene codes for a pentatricopeptide repeat (ppr) protein that is involved in mitochondrial gene expression and seed development. It is expressed in all maize tissues, including embryos and endosperm, leaves, roots, stems and ovaries since its product is necessary for the correct expression of a small subset of mitochondrial transcripts in the endosperm. However, the role of the gene in post-germinative development is still unclear. The aim of this study was to investigate that role.

Homozygous mutant seedlings lacking the EMP4 protein were obtained by cultivation of excised immature embryos to investigate the role of emp4 in the plant development after germination. Seedling leaf blades and primary roots of mutant maize were examined to analyze the effect of poor mitochondrial function on morphology and functionality of organelles. The effect of light on the mutants was also investigated. The kernels of mutants had significantly reduced endosperm and retarded embryo development. Mutant plants had reduced germination frequency as well as the proportion of seedlings reaching the first and second leaf stages.

Severe alterations were also observed in mutants such as the presence of empty cells or cells containing poorly organized organelles. Both mitochondria and chloroplast functionalities were also impaired. However, both structural and functional damage was less severe in seedlings grown in total darkness compared with those exposed to light thus suggesting that the effects of the mutation are enhanced by light.

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