Isolation and characterization of male flower cDNAs from maize

Differential screening of two libraries made from whole, immature maize tassels was used to isolate six cDNAs which show enhanced levels of expression in male flowers. MFS1, MFS2, MFS4, MFS10 and MFS18, which were isolated from a 5 cm tassel library, are expressed throughout tassel growth up until mature pollen is produced in the anthers. MFS14, which was isolated from a 10-12 cm tassel library, has a narrower window of expression associated with microsporogenesis and declines as mature pollen is produced. MFS18 mRNA accumulates in the glumes and in anther walls, paleas and lemmas of mature florets. MFS18 mRNA is particularly associated with the vascular bundle in the glumes and encodes a polypeptide of 12 kDa, rich in glycine, proline and serine that has similarities with other plant structural proteins. In contrast, MFS14 mRNA accumulates in the tapetum and encodes a polypeptide of 13 kDa that is rich in alanine. The MFS14 and MFS18 proteins are basic (isoelectric points of 11.56 and 9.54, respectively) and both have hydrophobic N-termini which display all the characteristics of signal peptides, indicating that these proteins may be secreted.