HOMOSERINE LACTONE-MEDIATED GENE-REGULATION IN PLANT-ASSOCIATED BACTERIA

Many plant-associated bacteria produce and utilize diffusible N-acyl-h omoserine lactones (AHLs) to regulate the expression of specific bacte rial genes and operons. AHL-mediated regulation utilizes two genes tha t encode proteins similar to the LuxI/LuxR system originally studied i n the marine symbiont Vibrio fischeri. The LuxI-type proteins are AHL synthases that assemble the diffusible AHL signal. The LuxR-type prote ins are AHL-responsive transcriptional regulatory proteins. LuxR prote ins control the transcription of specific bacterial genes in response to the levels of AHL signal. To date, AHL-mediated gene regulation has been identified in a broad range of gram-negative bacteria, most of w hich are host-associated. However, it seems unlikely that such a widel y conserved regulatory mechanism would be limited only to host-microbe interactions. These signals probably play central roles in ecological interactions among organisms in microbial communities by affecting co mmunication among bacterial populations as well as between bacterial p opulations and their eukaryotic hosts.