G. Serino et P. Maliga, RNA-POLYMERASE SUBUNITS ENCODED BY THE PLASTID RPO GENES ARE NOT SHARED WITH THE NUCLEUS-ENCODED PLASTID ENZYME, Plant physiology, 117(4), 1998, pp. 1165-1170
Plastid genes in photosynthetic higher plants are transcribed by at le
ast two RNA polymerases. The plastid rpoA, rpoB, rpoC1, and rpoC1, gen
es encode subunits of the plastid-encoded plastid RNA polymerase (PEP)
, an Escherichia coli-like core enzyme. The second enzyme is referred
to as the nucleus-encoded plastid RNA polymerase (NEP), since its subu
nits are assumed to be encoded in the nucleus. Promoters for NEP have
been previously characterized in tobacco plants lacking PEP due to tar
geted deletion of rpoB (encoding the beta-subunit) from the plastid ge
nome. To determine if NEP and PEP share any essential subunits, the rp
oA, rpoC1, and rpoC2 genes encoding the PEP alpha-, beta'-, and beta '
'-subunits were removed by targeted gene deletion from the plastid gen
ome. We report here that deletion of each of these genes yielded photo
synthetically defective plants that lack PEP activity while maintainin
g transcription specificity from NEP promoters. Therefore, rpoA, rpoB,
rpoC1, and rpoC2 encode PEP subunits that are not essential component
s of the NEP transcription machinery. Furthermore, our data indicate t
hat no functional copy of rpoA, rpoB, rpoC1, or rpoC2 that could compl
ement the deleted plastid rpo genes exists outside the plastids.