Tobacco bZIP factor TGA10 is a novel member of the TGA family of transcription factors.

TGA factors constitute a family of conserved plant bZ1P transcription factors that regulate transcription from as-1-like elements in response to plant signalling molecules salicylic acid (SA), methyl jasmonate (MJ) and auxin. Based on sequence similarities, two subclasses of TGA factors have been identified before in tobacco: class I factors (TGA1a and PG13) are preferentially expressed in root tip meristems, whereas class II factors (TGA2.1 and TGA2.2) are found in leaves and in roots. Here we describe a novel member of the tobacco TGA family (TGA10), which defines a distinct subclass of its own. TGA10 mRNA and TGA10 protein were found in roots but not in leaves of mature tobacco plants. TGA10 binds specifically to the as-1 element, interacts with TGA2.2, and activates transcription in yeast. When ectopically expressed in leaves, TGA10 enhanced SA-, auxin- and MJ-inducibility of target gene Nt103, which responds in the same manner to enhanced levels of TGA2.2. This indicates that TGA10, albeit normally not present in leaves, can interact with the leaf regulatory network controlling transcription from as-1-containing promoters. However, Nt103 expression was not affected in roots of TGA10-over-expressing plants, implying the existence of root-specific mechanisms which do not allow a positive effect of increased TGA10 levels on target gene expression.