Analysis Of A Knock-out Mutant Of An Arabidopsis T7 Phage-Type RNA Polymerase, RpoTp (RpoT;3)

Abstract

Genes harbored on the plastid genome are transcribed by two types of RNA polymerases, eubacteria-type plastid-encoded RNA polymerase (PEP) and T7 phage-type nuclear-encoded RNA polymerase (NEP). In Arabidopsis thaliana, three T7 phage type RNA polymerase genes have been identified, and RpoTp and RpoTmp were suggested to localize in plastids. We have isolated a T-DNA inserted mutant in the rpoTp gene, identical to sca3-2. The mutant's seedlings showed almost albino, very poor growth and loss of glycolipids. We also found that the mutant cotyledons partially re-developed chloroplasts on MS-plates containing sucrose. Interestigly, the mesophyll cells of the mutant rosette leaves contained different type of aberrant plastids. This observation would suggest that RpoTp is necessary for synchronous proceeding of chloroplast development in a cell. We will discuss the functional difference between RpoTp and RpoTmp.