ABSTRACT
DNA methylation is a dynamic epigenetic mechanism that plays a significant role in gene expression and also maintains chromatin stability. The process is conserved in both plants and animals, and crucial for development and stress responses. Differential DNA methylation during adverse environmental conditions or pathogen attack facilitates the selective expression of defense-related genes. Both stress-induced DNA hypomethylation and hypermethylation play beneficial roles in activating the defense response. These DNA marks may be carried to the next generation making the progenies 'primed' for abiotic and biotic stress responses. Over the recent years, rapid advancements in the area of high throughput sequencing have enabled the detection of methylation status at genome levels in several plant species. Epigenotyping offers an alternative tool to plant breeders in addition to conventional markers for the selection of the desired offspring. In this review, we briefly discuss the mechanism of DNA methylation, recent understanding of DNA methylation-mediated gene regulation during abiotic and biotic stress responses, and stress memory in plants.
Subject(s)
DNA Methylation , Gene Expression Regulation, Plant , Animals , Chromatin , DNA Methylation/genetics , Epigenesis, Genetic , Gene Expression Regulation, Plant/genetics , Plants/genetics , Stress, Physiological/geneticsABSTRACT
KEY MESSAGE: BjuWRR1, a CNL-type R gene, was identified from an east European gene pool line of Brassica juncea and validated for conferring resistance to white rust by genetic transformation. White rust caused by the oomycete pathogen Albugo candida is a significant disease of crucifer crops including Brassica juncea (mustard), a major oilseed crop of the Indian subcontinent. Earlier, a resistance-conferring locus named AcB1-A5.1 was mapped in an east European gene pool line of B. juncea-Donskaja-IV. This line was tested along with some other lines of B. juncea (AABB), B. rapa (AA) and B. nigra (BB) for resistance to six isolates of A. candida collected from different mustard growing regions of India. Donskaja-IV was found to be completely resistant to all the tested isolates. Sequencing of a BAC spanning the locus AcB1-A5.1 showed the presence of a single CC-NB-LRR protein encoding R gene. The genomic sequence of the putative R gene with its native promoter and terminator was used for the genetic transformation of a susceptible Indian gene pool line Varuna and was found to confer complete resistance to all the isolates. This is the first white rust resistance-conferring gene described from Brassica species and has been named BjuWRR1. Allelic variants of the gene in B. juncea germplasm and orthologues in the Brassicaceae genomes were studied to understand the evolutionary dynamics of the BjuWRR1 gene.
Subject(s)
Disease Resistance/genetics , Genes, Plant , Mustard Plant/genetics , Mustard Plant/microbiology , Oomycetes/physiology , Plant Diseases/microbiology , Proteins/genetics , Alleles , Amino Acid Sequence , Base Sequence , Evolution, Molecular , Gene Expression Regulation, Plant , Genetic Association Studies , Genetic Markers , Genetic Variation , Leucine-Rich Repeat Proteins , Oomycetes/isolation & purification , Plants, Genetically Modified , Proteins/chemistry , Proteins/metabolism , Transformation, GeneticABSTRACT
White rust, causal agent oomycete Albugo candida, is a significant disease of the cultivated Brassica species. The Indian gene pool lines of oilseed mustard, Brassica juncea, are highly susceptible to the pathogen. Resistance to A. candida has been reported in the east European gene pool lines of mustard and mapped to LG A4 in line Heera and LG A5 in line Donskaja-IV. A new resistance-conferring locus to A. candida isolate AcB1 has been mapped to LG A6 of B. juncea line Tumida-a Chinese vegetable type mustard using an F1DH mapping population that has been developed from a Tumida × Varuna (susceptible Indian gene pool line) cross. A molecular map containing 8,303 genic and GBS markers was used to map the resistance trait to an interval of 63.0 cM-70.8 cM on LG A6. Genome assemblies of Tumida and Varuna were used to find the genes present within the flanking markers discerned by genetic mapping. The most likely candidate gene in the mapped interval is BjuA046215, a CC-NBS-LRR (CNL) type R gene that encodes a protein with all the specific subdomains of the proteins encoded by such genes. Alleles of BjuA046215 in Varuna and other lines of the Indian and the east European gene pools encode proteins that have truncated LRR domains. Analysis of the syntenic regions in some of the Brassicaceae genomes and phylogenetic analysis of CNL type R genes showed BjuA046215 to be closely related to a recently described white rust resistance-conferring R gene BjuWRR1 in B. juncea Donskaja-IV, both belonging to the CNL-D group of R genes. Related R genes in Arabidopsis thaliana confer resistance to another oomycete, Peronospora parasitica.
