The protein named PRETY (protein repressor of TATA element from Xylella) controls the expression of five genes of unknown function arranged in a single operon. This operon is conserved in some plant pathogenic bacteria including Xylella fastidiosa, Agrobacterium tumefaciens and other root-associated bacteria. The aim of this project is to elucidate the biological function of PRETY and its target genes. PRETY shows similarities to metal-responsive transcriptional repressors ArsR and SmtB, which control tolerance and detoxification of heavy metals in prokaryotes. However, the PRETY operon differs remarkably from the ArsR and SmtB types of operon since it does not contain the same effector proteins like thioneins and ATPases. Instead, the PRETY operon contains, in addition to PRETY, three predicted membrane permeases and a putative glyoxalase II/beta-latamase (BLH), a member of the beta-lactamase super family. In this work we show that PRETY binds to a TATA box-like element comprising a 9-4-9 palindrome in the BLH promoter and repress transcription of a reporter gene under the control of the BLH promoter providing evidence for its role as a transcriptional repressor in X. fastidiosa and A. tumefaciens.  Although binding of PRETY to its target DNA was diminished in the presence of cadmium, copper and iron, the regulation of the operon by PRETY in response to these metals could not be demonstrated in vivo using Xylella and Agrobacterium cells carrying a reporter plasmid. Structural studies show that PRETY multimerizes in solution and changes its secondary structure in the presence of the target DNA. The use of subtracts for beta-lactamase, lactonases and glyoxalases, as well as hypoxia and nutrient deficiency did not alter the expression of the operon. Similarly, the activity of the reporter genes in Agrobacterium and Xylella did not change when the bacteria were in contact with the plant or with plant extracts. On the other hand, both Agrobacterium and Xylella reporter cells showed a significant increase in the operon activity during the biofilm formation indicating a possible function related to a quorum-sensing system.