Maturation and Secretion of a Serine Proteinase is Associated with Events of Late Microsporogenesis

An antiserum against meiotic proteins which bind to DNA cellulose was generated as a tool to assist the identification and purification of microsporogenesis-specific proteins. In immunoblotting experiments, this antiserum identified three meiotic proteins which are differentially expressed in anthers during microsporogenesis. One of these proteins was purified and characterized by biochemical and immunological techniques. This 82 kDa protein is synthesized as a preproprotein, acquires glycans as it moves through the endoplasmic reticulum and Golgi body, and is secreted into the anther locule. Immunocytochemical experiments demonstrate that the protein is expressed primarily in tapetal cells, and reaches peak concentrations as the microsporocytes reach the tetrad stage. Zymogram analyses and protein sequence comparisons indicate that the protein is a member of the serine proteinase family. The possible roles of the proteinase in microsporogenesis and pollen development are discussed.