The maizeempty 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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