Small Antisense RNA RblR Positively Regulates RuBisCo in Synechocystis sp. PCC 6803

Abstract

Small regulatory RNAs (sRNAs) function as transcriptional and post-transcriptional regulators of gene expression in organisms from all domains of life. Cyanobacteria are thought to have developed a complex RNA-based regulatory mechanism. In the current study, by genome-wide analysis of differentially expressed small RNAs in <i>Synechocystis</i> sp. PCC 6803 under high light conditions, we discovered an asRNA (RblR) that is 113nt in length and completely complementary to its target gene <i>rbcL</i>, which encodes the large chain of RuBisCO, the enzyme that catalyzes carbon fixation. Further analysis of the RblR(+)/(-) mutants revealed that RblR acts as a positive regulator of <i>rbcL</i> under various stress conditions; Suppressing RblR adversely affects carbon assimilation and thus the yield, and those phenotypes of both the wild type and the overexpressor could be downgraded to the suppressor level by carbonate depletion, indicated a regulatory role of RblR in CO₂ assimilation. In addition, a real-time expression platform in <i>Escherichia coli</i> was setup and which confirmed that RblR promoted the translation of the <i>rbcL</i> mRNA into the RbcL protein. The present study is the first report of a regulatory RNA that targets RbcL in <i>Synechocystis</i> sp. PCC 6803, and provides strong evidence that RblR regulates photosynthesis by positively modulating <i>rbcL</i> expression in <i>Synechocystis</i>.