Trans-Factor PTF1 Participates in the Response to Salinity but Does Not Regulate Expression of the psbD Gene in Arabidopsis thaliana

The existing data on the role of PTF1/TCP13 belonging to the TCP family of transcription factors in regulating expression of a psbD plastid gene encoding a D2 protein of PSII are controversial. To analyze biological functions of PTF1/TCP13, transformed plants expressing PTF1/TCP13 under a beta-estradiol-inducible promoter were used. PTF1/TCP13 overexpression did not provide the expected increase in the accumulation of psbD transcripts transcribed from BLRP (Blue Light Responsive Promoter), though their level significantly increased under exposure to light or abscisic acid (ABA). PTF1/TCP13 was up-regulated by ABA; moreover, genes of the canonic pathway of the ABA signal transduction were involved in the regulation of PTF1/TCP13 expression. In addition, PTF1/TCP13 was induced in response to salt stress However, in the overexpressing line, salt tolerance and expression of salt stress markers, as well as a number of genes for the synthesis and signaling of ABA, were reduced compared to plants with the normal level of expression of this transcription factor, that is, PTF1/TCP13 acted as a negative regulator of salt stress Thus, PTF1 does not belong to plastid transcription factors. Nevertheless, it represents one of the components of the ABA-dependent regulatory chain capable of modifying expression of nuclear and chloroplast genes in response to changes in homeostasis.