A low molecular weight proteome comparison of fertile and male sterile 8 anthers of Zea mays

During maize anther development, somatic locular cells differentiate to support meiosis in the pollen mother cells. Meiosis is an important event during anther growth and is essential for plant fertility as pollen contains the haploid sperm. A subset of maize male sterile mutants exhibit meiotic failure, including ms8 (male sterile 8) in which meiocytes arrest as dyads and the locular somatic cells exhibit multiple defects. Systematic proteomic profiles were analysed in biological triplicates plus technical triplicates comparing ms8 anthers with fertile sibling samples at both the premeiotic and meiotic stages; proteins from 3.5 to 20 kDa were fractionated by 1-D PAGE, cleaved with Lys-C and then sequenced using a LTQ Orbitrap Velos MS paradigm. Three hundred and 59proteins were identified with two or more assigned peptides in which each of those peptides were counted at least two or more times (0.4% peptide false discovery rate (FDR) and 0.2% protein FDR); 2761 proteins were identified with one or more assigned peptides (0.4% peptide FDR and 7.6% protein FDR). Stage-specific protein expression provides candidate stage markers for early anther development, and proteins specifically expressed in fertile compared to sterile anthers provide important clues about the regulation of meiosis. 49% of the proteins detected by this study are new to an independent whole anther proteome, and many small proteins missed by automated maize genome annotation were validated; these outcomes indicate the value of focusing on low molecular weight proteins. The roles of distinctive expressed proteins and methods for mass spectrometry of low molecular weight proteins are discussed.