EMB-7L is required for embryogenesis and plant development in maize involved in RNA splicing of multiple chloroplast genes

Abstract

Embryo and endosperm originate from the double fertilization, but they have different developmental fates and biological functions. We identified a previously undescribed maize seed mutant, wherein the embryo appears to be more severely affected than the endosperm (embryo-specific, emb). In the W22 background, the emb embryo arrests at the transition stage whereas its endosperm appears nearly normal in size. At maturity, the embryo in W22-emb is apparently small or even invisible. In contrast, the emb endosperm develops into a relative normal size. We cloned the mutant gene on the Chromosome 7L and designated it emb-7L. This gene is generally expressed, but it has a relatively higher expression level in leaves. Emb-7L encodes a chloroplast-localized P-type pentatricopeptide repeat (PPR) protein, consistent with the severe chloroplast deficiency in emb-7L albino seedling leaves. Full transcriptome analysis of the leaves of WT and emb-7L seedlings reveals that transcription of chloroplast protein-encoding genes are dramatically variable with pre-mRNA intron splicing apparently affected in a tissue-dependent pattern and the chloroplast structure and activity were dramatically affected including chloroplast membrane and photosynthesis machinery component and synthesis of metabolic products (e.g., fatty acids, amino acids, starch).