Expression of Chloroplast and Mitochondrial Genes during Microsporogenesis in Maize.

Mitochondrial and plastid gene expression has been examined during maize (Zea mays) microsporogenesis. Accumulation of transcripts was found for three mitochondrial genes studied (cob, atp6, and atp9) at the mid-term of pollen development. In contrast, these mitochondrial transcripts were undetectable in mature pollen. Southern and DNA gel blot experiments showed that the copy number of mitochondrial genes was amplified in microspores at stages preceding the accumulation of these transcripts. Plastid transcripts of the photosynthetic psbA and rbcL genes could not be detected after the two mitoses, whereas precursors of the 16S rRNA are detected at low levels.