Regulation of Cyclic Lipopeptide Orfamide A Biosynthesis in Pseudomonas protegens by the Gac-Rsm-LuxR Cascade

In this study, we investigated the regulatory interactions among the GacS/A two-component system, small RNAs (sRNAs), repressor proteins, and two LuxR-type transcription factors in orfamide A biosynthesis. We found that GacS/A indirectly regulates orfamide A production by enhancing transcription of three sRNAs (RsmX, RsmY and RsmZ).

RsmY and RsmZ synergistically relieve repression by RsmA and RsmE, while RsmX plays a lesser role, likely counteracting only one repressor. LuxR-type transcription factors LuxR1 and LuxR2, which positively regulate orfamide A synthesis, are directly repressed by RsmA and RsmE via binding to their 5′ untranslated regions, linking them to the Gac-Rsm signaling cascade. We further demonstrate that LuxR2 activates luxR1 expression, which in turn facilitates orfamide A production by binding to the promoter of the orfamide A biosynthetic gene cluster.