A genome-wide association study on growth traits in orangespotted grouper(Epinephelus coioides) with RAD-seq genotyping

The orange-spotted grouper, Epinephelus coioides, is one of the most popular fish in China and Southeast Asian countries because of its important economic value. However, molecular mechanism underlying the growth of orange-spotted grouper has never been fully understood. Herein, we performed a genome-wide association study （GWAS） on a natural population of 198 individuals aiming to screen the whole genome of orange-spotted grouper for identification of growth-related loci by restriction-site associated DNA sequencing. In this research, 261,366 single nucleotide polymorphisms （SNPs） were developed, in which 110 SNPs were identified to be correlated with growth and 20 SNPs were further confirmed to be associated with both body weight and total length. From these identified SNPs, we annotated a total of 34 genes, including adgrb2, csnkzal, cers5, co122al, creb5, dndl, dzankl, dnail, npy2r, fat3, lrrk2, lrp5, map3k9, and so on. Among these candidate genes, npy2r （neuropeptide Y receptor Y2） was reported to play a critical role in growth of the orange-spotted grouper. In addition, population structure, principal component analysis, kinship matrix and linkage disequilibrium were examined to verify the accuracy and reliability of our GWAS results. Our data will also provide a valuable genetic resource for further marker-assisted selection program to improve growth quality in groupers.

A novel protein complex that regulates active DNA demethylation in Arabidopsis

Active DNA demethylation is critical for altering DNA methylation patterns and regulating gene expression.The 5-methylcytosine DNA glycosylase/lyase ROS1 initiates a base-excision repair pathway for active DNA demethylation and is required for the prevention of DNA hypermethylation at 1000 s of genomic regions in Arabidopsis.How ROS1 is regulated and targeted to specific genomic regions is not well understood.Here,we report the discovery of an Arabidopsis protein complex that contains ROS1,regulates ROS1 gene expression,and likely targets the ROS1 protein to specific genomic regions.ROS1 physically interacts with a WD40 domain protein(RWD40),which in turn interacts with a methyl-DNA binding protein(RMB1)as well as with a zinc finger and homeobox domain protein(RHD1).RMB1 binds to DNA that is methylated in any sequence context,and this binding is necessary for its function in vivo.Loss-of-function mutations in RWD40,RMB1,or RHD1 cause DNA hypermethylation at several tested genomic regions independently of the known ROS1 regulator IDM1.Because the hypermethylated genomic regions include the DNA methylation monitoring sequence in the ROS1 promoter,plants mutated in RWD40,RMB1,or RHD1 show increased ROS1 expression.Importantly,ROS1 binding to the ROS1 promoter requires RWD40,RMB1,and RHD1,suggesting that this complex dictates ROS1 targeting to this locus.Our results demonstrate that ROS1 forms a protein complex with RWD40,RMB1,and RHD1,and that this novel complex regulates active DNA demethylation at several endogenous loci in Arabidopsis.

Roles of DEMETER in regulating DNA methylation in vegetative tissues and pathogen resistance

DNA methylation is an epigenetic mark important for genome stability and gene expression.In Arabidopsis thaliana,the 5-methylcytosine DNA glycosylase/demethylase DEMETER(DME)controls active DNA demethylation during the reproductive stage;however,the lethality of loss-of-function dme mutations has made it difficult to assess DME function in vegetative tissues.Here,we edited DME using clustered regularly interspaced short palindromic repeats(CRISPR)/CRISPR-associated protein 9 and created three weak dme mutants that produced a few viable seeds.We also performed central cell-specific complementation in a strong dme mutant and combined this line with mutations in the other three Arabidopsis demethylase genes to generate the dme ros1 dml2 dml3(drdd)quadruple mutant.A DNA methylome analysis showed that DME is required for DNA demethylation at hundreds of genomic regions in vegetative tissues.A transcriptome analysis of the drdd mutant revealed that DME and the other three demethylases are important for plant responses to biotic and abiotic stresses in vegetative tissues.Despite the limited role of DME in regulating DNA methylation in vegetative tissues,the dme mutants showed increased susceptibility to bacterial and fungal pathogens.Our study highlights the important functions of DME in vegetative tissues and provides valuable genetic tools for future investigations of DNA demethylation in plants.