The tale of two RNA polymerases: Transcription profiling and gene expression strategy of bacteriophage Xp10

Bacteriophage Xp10 infects rice pathogen Xanthomonas oryzae. Xp10 encodes its own single-subunit RNA polymerase (RNAP), similar to that found in phages of the T7 family. On the other hand, most of Xp10 genes are organized in a manner typical of lambdoid phages that are known to rely only on host RNAP for their development. To better understand the temporal pattern of viral transcription during Xp10 development, we performed global transcription profiling, primer extension, chemical kinetic modelling and bioinformatic analyses of Xp10 gene expression. Our results indicate that true to its mosaic nature, Xp10 relies on both host and viral RNAPs for expression of genes coding for virion components and host lysis. The joint transcription of the same set of genes by two types of RNA polymerases is unprecedented for a bacteriophage. Curiously, such a situation is realized in chloroplasts.