Minisymposium 16: Gene Regulation

Abs # 28003: Salicylic acid and NPR1 mediate in vivo promoter-specific recruitment of trans-activating TGA factors of Arabidopsis

Presenter:	Arias, Jonathan , arias@umbi.umd.edu
Authors	Arias, Jonathan  (A) (B)  Johnson, Christopher  (A) (B)  Boden, Erin  (A)   Town, Christopher  (C)
Affiliations:	(A): Center for Biosystems Research, University of Maryland Biotechnology Institute, (B): Program in Molecular and Cell Biology, University of Maryland, College Park (C): The Institute for Genomic Research

In higher plants, as-1-type cis-elements and their cognate TGA factors confer transcription in response to the defense hormone salicylic acid (SA). The promoter of At PR-1 contains an as-1-type element (LS7) that activates expression of this defense gene through a signal pathway involving SA and as we show, the mediator protein NPR1. The present study focuses on potential trans-regulatory contributions to PR-1 expression in leaves by two NPR1-interacting TGA factors, termed TGA2 and TGA3. SA-induced activation of PR-1 may result from a change in the DNA-binding activity of these TGA factors. Gel-shift assays showed that both factors are principal contributors to the LS7-binding activity of leaf nuclear proteins, and that this activity was markedly enhanced through an SA signal pathway involving NPR1. These findings were validated by plant chromatin immunoprecipitation (pChIP) assays of leaves from wild-type and npr1 mutant plants, whereby it was found that both factors in vivo are recruited to the PR-1 promoter in response to SA through NPR1. In the context of results presented here, the apparent differential distribution of TGA2 and TGA3 in young and mature leaves (Pontier et al., Plant J. 32:641, 2002) suggests that they confer different cell- or development-specific contributions to PR-1 activity. Lastly, leaf biolistic transfection assays revealed that TGA3 is an SA-responsive trans-activator, as previously described for TGA2. These results offer new insight on regulatory contributions by specific TGA factors to the expression of defense genes and serve as an important paradigm for our ongoing 2010-funded project to map genome-wide binding sites of these and other TGA factors with our colleague Gary Stormo (Wash. Univ. Med School). In this context, ongoing efforts by this group to design, construct and use an Arabidopsis intergenic promoter DNA array for high-throughput ChIP studies of TGA factors will be discussed, including recent findings on global contributions by TGA2 and TGA3 to defense gene networks.