The male sterile 8 mutation of maize disrupts the temporal progression of the transcriptome and results in the mis-regulation of metabolic functions

Abstract

Maize anther ontogeny is complex, with the expression of more than 30,000 genes over 4 days of cell proliferation, cell fate acquisition and the start of meiosis. Although many male-sterile mutants disrupt these key steps, few have been investigated in detail. The terminal phenotypes of Zea mays (maize) male sterile 8 (ms8) are small anthers exhibiting meiotic failure. Here, we document much earlier defects: ms8 epidermal cells are normal in number but fail to elongate, and there are fewer, larger tapetal cells that retain, rather than secrete, their contents. ms8 meiocytes separate early, have extra space between them, occupied by excess callose, and the meiotic dyads abort. Thousands of transcriptome changes occur in ms8, including ectopic activation of genes not expressed in fertile siblings, failure to express some genes, differential expression compared with fertile siblings and about 40% of the differentially expressed transcripts appear precociously. There is a high correlation between mRNA accumulation assessed by microarray hybridization and quantitative real-time reverse transcriptase polymerase chain reaction. Sixty-three differentially expressed proteins were identified after two-dimensional gel electrophoresis followed by liquid chromatography tandem mass spectroscopy, including those involved in metabolism, plasmodesmatal remodeling and cell division. The majority of these were not identified by differential RNA expression, demonstrating the importance of proteomics in defining developmental mutants.