The Chlamydia trachomatis plasmid-encoded Pgp4 is a transcriptional regulator of virulence associated chromosomal genes

Chlamydia trachomatis causes chronic inflammatory diseases of the eye and genital tract of global medical importance. The chlamydial plasmid plays an important role in the pathophysiology of these diseases as plasmid-deficient organisms are highly attenuated. The plasmid encodes both noncoding RNAs and eight conserved ORFs of undefined function. To understand plasmid gene function we generated plasmid shuttle vectors with deletions in each of the eight ORFs. The individual deletion mutants were used to transform chlamydiae and the transformants were characterized in terms of plasmid biology and transcriptional profiling. We show that pgp1-2, -6 and -8 are essential for plasmid maintenance while the other ORFs can be deleted and the plasmid stably maintained. We further show that a pgp4 knockout mutant exhibits an in vitro phenotype similar to its isogenic plasmid-less strain in terms of abnormal inclusion morphology and lack of glycogen accumulation. Microarray and qRT-PCR analysis revealed that pgp4 is involved in transcriptional regulation of multiple chromosomal genes; including the glycogen synthase gene glgA. Based on our results, we propose that Pgp1 is a plasmid replicative helicase, Pgp2 is a plasmid replication protein, Pgp4 is a transcriptional regulator of virulence associated chromosomal genes, and Pgp6-8 are plasmid partitioning proteins. These findings have important implications for understanding the plasmid’s role in chlamydial pathogenesis and the development of novel antigenically multivalent live-attenuated chlamydial vaccines. Chlamydia trachomatis wild type vs. two deletion mutants, and mock