TAL (transcription activator-like) effectors (often referred to as
TALEs but not to be confused with the
three
amino acid
loop
extension family of proteins) are
proteins secreted by
Xanthomonas bacteria via their
type III secretion system when they infect various
plant species. These proteins can bind
promoter sequences in the host plant and activate the
expression of plant genes that aid bacterial infection. They recognize plant
DNA sequences through a central repeat domain consisting of a variable number of ~34 amino acid repeats. There appears to be a one-to-one correspondence between the identity of two critical amino acids in each repeat and each DNA base in the target sequence. These proteins are interesting to researchers both for their role in disease of important crop species and the relative ease of retargeting them to bind new DNA sequences. Similar proteins can be found in the pathogenic bacterium
Ralstonia solanacearum and
Burkholderia rhizoxinica