Truncated and dispersed rpl2 and rps19 pseudogenes are co-transcribed withneighbouring downstream genes in wheat mitochondria

The wheat mitochondrial genome contains only partial coding sequences for t he L2 and S19 ribosomal proteins, unlike in rice or liverwort mitochondria, where these genes are functional and have a bacterial-type linkage. A sing le-copy stretch corresponding to the extreme 3 ' terminus of the wheat rpl2 gene is co-transcribed with the trans-splicing nad1 exon 4, and. at anothe r unique location, the rps19 segment lacking the 5 ' coding region is co-tr anscribed with the downstream nad4L gene. In both cases, the 5 ' termini of these transcripts map to promoter consensus motifs acquired through genomi c reorganization, enabling continued expression of essential downstream gen es. In both wheat and rice. the rpl2 and rps19 genomic regions differ in th eir RNA profiles between germinating embryos and seedlings. The absence of intact rpl2 and rps19 genes in wheat mitochondria is consistent with their inactivation through DNA rearrangement/deletion after the successful transf er of functional copies to the nucleus.