Investigating the role of Epigenetic Regulators in Plant Nitrogen Use.docx

Nitrogen (N) is a macronutrient required for plant growth and is a major constituent of nucleic acids and proteins that are essential for several life processes. Plant response to N has been well understood at a molecular level but little is known about the chromatin or epigenetic level regulation of N response. Uncovering the epigenetic level regulation essential for plant N signaling and response is essential to improving our molecular understanding of N use efficiency (NUE). To fill this knowledge gap, we first performed a meta-analysis intersecting the published transcriptomic study of N-responsive genes in Arabidopsis thaliana with EpiNet, an extensive epigenetic regulatory network previously constructed in our lab through machine learning approaches, to identify a list of 18 potential epigenetic regulators that are predicted to control N response in plants. Next, by adopting a reverse genetics approach, we aimed to validate the in-silico prediction of these essential epigenetic regulators. To do this, we grew T-DNA insertional mutants for the genes encoding these epigenetic regulators, along with wild-type controls, under high and low N conditions, and compared them in various physiological traits. Our results indicate that 8 out of 10 confirmed knock-down mutants do show altered N-responsive phenotypes in comparison to the wild type. One of the mutants, ashr2-1, which is mutated in a gene encoding a putative SET-domain containing group protein (SDG) of putative histone methyltransferase, displayed reduced growth of primary root compared to WT in response to N. We performed RNA-sequencing to identify the differentially expressed genes that are induced or repressed by ASHR2 in N treatments to gain further insight into the molecular underpinnings of the ASHR2-mdediated N response in roots. In summary, our study has revealed knowledge on important epigenetic regulators in plant N responses, which has the potential to be extended to crop species as novel targets for enhancing NUE.