Ph.D. Program in Plant Molecular Biology

Friday Seminar by Dr. Vijay Gahlaut

PK Lab/ Friday/ September 28, 2018/ 3.30 pm/ Role of RNA-directed DNA methylation (RdDM) in abiotic stress regulation in plants
Category: Research

Role of RNA-directed DNA methylation (RdDM) in Abiotic Stress Regulation in Plants

Dr. Vijay Gahlaut


Plants frequently encounter abiotic stress conditions such as heat, cold, drought and salinity. Adaptive strategies of plants to cope with these stresses are complex and depend on the precise and timely regulation of stress-responsive gene networks. In response to stress, genome-wide transcriptional reprogramming is required for the regulation of genes involved in stress protection and genes that encode regulatory proteins. RNA-directed DNA methylation (RdDM), first discovered in viroid-infected tobacco, is an important regulatory pathway; involved in repressive epigenetic modifications that can trigger transcriptional gene silencing. RdDM is implicated in abiotic stress responses as well as pathogen defense, biotic stress, reproduction, and in inter-allelic and inter-cellular communication. In Arabidopsis, it has been shown that heat stress affects epigenetic gene silencing via RdDM. The mutants defective in DNA methylation, histone modifications, chromatin-remodeling, or siRNA-based silencing pathways was analyzed for heat tolerance. Plants deficient in NRPD2 (subunit of RNA polymerases IV and V) and HDA6 (Rpd3-typehistone deacetylase) were hypersensitive to heat exposure. Moreover, microarray analysis demonstrated that NRPD2 and HDA6 have independent roles in transcriptional reprogramming in response to heat stress; and ultimately suggested that HS response in Arabidopsis relies on the integrity of RdDM pathway and provide evidence that heat-dependent gene expression is influenced by closely located transposon sequences. In another study, AtMYB74 has been found to be transcriptionally regulated by RdDM as a response to salt stress in Arabidopsis. Bisulphite sequencing indicated that 24-nt siRNAs target a region approximately 500 bp upstream of the transcription initiation site of AtMYB74, which is heavily methylated. Levels of DNA methylation in this region were significantly reduced in wild type plants under salt stress, whereas no changes were found in RdDM mutants. Also, transgenic plants overexpressing AtMYB74 displayed hypersensitivity to NaCl during seed germination. The above studies provide evidences that the transcriptional response to abiotic stresses relies or regulated via RdDM pathway.