Characterization of MZm3-3, a Zea mays tapetum-specific transcript.

A cDNA, MZm3-3, was isolated by differential screening of a cDNA library from Zea mays meiotic stage anthers against cDNA of 3-week-old seedlings. Characterization of this cDNA indicated that the MZm3-3 gene is expressed specifically during male gametogenesis. Its expression is highly and preferentially detected in the tapetum, from the pollen mother cell to uninucleated microspore stages. It encodes a short alkaline protein of 10.6 kDa, with a conserved pattern of eight cysteine residues. Sequence analysis showed that these features are shared with lipid transfer proteins and some male-flower-specific proteins. The presence of a putative signal peptide indicates that MZm3-3 enters into the secretory pathway to then be released into the anther loculus. Based on these features, the secretory activity of the tapetum and the temporal expression pattern of MZm3-3, a contribution to pollen coat formation is suggested. Southern blot analyses demonstrated the presence of closely related genes, indicating that MZm3-3 belongs to a multigene family.