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A pathogen-activated transcription program directed by TFIIB-related pBrp1 in plant immunity


Plant pathogens can lead to severe crop yield loss, thereby threatening global food security. Understanding the molecular mechanisms of plant immunity will ultimately help develop better disease control strategies. An integral part of plant immunity is the activation of a large number of defense-related genes upon pathogen infection. This project is focused on a potential master regulator of plant defense gene expression with a critical role in plant immunity. The main goals of the project are to i) identify the spectrum of genes that are directly regulated by the regulator, ii) establish the mechanisms by which the regulator activates plant defense-related genes and iii) determine the regulation of the regulator during the activation of plant immune responses. Results from this project will enhance our understanding of the process of differential gene expression fundamental not only to plant immune systems but also to all complex processes in living organisms. This project will integrate research with training, learning, diversity and outreach activities. Postdoctoral fellows and students working on the project will receive interdisciplinary training in a wide range of molecular approaches. The project will be integrated into classroom learning for students, including those from underrepresented groups and high school students, to increase the general public's awareness of science and technology.<br/> <br/>Transcription reprogramming in plant immunity is achieved through concerted action of specific transcription factors (TFs) through recruitment or release of RNA polymerase II (RNAP II). The RNAP II holoenzyme contains a group of general TFs (GTFs), which are believed to be required for transcription of all genes. Transcription factor IIB (TFIIB) is a GTF for RNAP II. Interestingly, Arabidopsis have 14 genes encoding TFIIB-related proteins including six plant-specific TFIIB-related proteins (pBrps). This project is focused on Arabidopsis pBrp1. The pbrp1 mutants are compromised in both disease resistance and defense gene expression. In uninfected plants, the pBrp1 protein is retained on the plastid envelop and nuclear pBrp1 is detected only when proteasome pathways are inhibited. Pathogen infection induces pBrp1 accumulation. These results suggest that pBrp1 is a regulated GTF of a special RNAP II holoenzyme that directs a defense gene transcription program. To test this hypothesis, the project will identify the direct target genes of pBrp1 using genome-wide transcriptome profiling and ChIP-seq. The direct association of pBrp1 with RNAP II will be determined using co-immunoprecipitation to confirm pBrp1 is a GTF for RNAP II and to identify other components in the complexes with roles in the action and regulation of pBrp1. The protein levels and nuclear translocation of pBrp1 will be manipulated to determine the importance of the tight regulation of pBrp1 for balancing plant defense with fitness. These studies will help elucidate transcriptional regulation of plant immunity, as well as the intricate mechanisms for timely, accurate and effective activation of plant defense.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Zhixiang Chen
Purdue University
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