ABSTRACT
BACKGROUND: Genetic variation in regulatory sequences that alter transcription factor (TF) binding is a major cause of phenotypic diversity. Brassinosteroid is a growth hormone that has major effects on plant phenotypes. Genetic variation in brassinosteroid-responsive cis-elements likely contributes to trait variation. Pinpointing such regulatory variations and quantitative genomic analysis of the variation in TF-target binding, however, remains challenging. How variation in transcriptional targets of signaling pathways such as the brassinosteroid pathway contributes to phenotypic variation is an important question to be investigated with innovative approaches. RESULTS: Here, we use a hybrid allele-specific chromatin binding sequencing (HASCh-seq) approach and identify variations in target binding of the brassinosteroid-responsive TF ZmBZR1 in maize. HASCh-seq in the B73xMo17 F1s identifies thousands of target genes of ZmBZR1. Allele-specific ZmBZR1 binding (ASB) has been observed for 18.3% of target genes and is enriched in promoter and enhancer regions. About a quarter of the ASB sites correlate with sequence variation in BZR1-binding motifs and another quarter correlate with haplotype-specific DNA methylation, suggesting that both genetic and epigenetic variations contribute to the high level of variation in ZmBZR1 occupancy. Comparison with GWAS data shows linkage of hundreds of ASB loci to important yield and disease-related traits. CONCLUSION: Our study provides a robust method for analyzing genome-wide variations of TF occupancy and identifies genetic and epigenetic variations of the brassinosteroid response transcription network in maize.
Subject(s)
Brassinosteroids , Zea mays , Zea mays/genetics , Alleles , Chromatin Immunoprecipitation Sequencing , Phenotype , Transcription Factors/geneticsABSTRACT
We report de novo genome assemblies, transcriptomes, annotations, and methylomes for the 26 inbreds that serve as the founders for the maize nested association mapping population. The number of pan-genes in these diverse genomes exceeds 103,000, with approximately a third found across all genotypes. The results demonstrate that the ancient tetraploid character of maize continues to degrade by fractionation to the present day. Excellent contiguity over repeat arrays and complete annotation of centromeres revealed additional variation in major cytological landmarks. We show that combining structural variation with single-nucleotide polymorphisms can improve the power of quantitative mapping studies. We also document variation at the level of DNA methylation and demonstrate that unmethylated regions are enriched for cis-regulatory elements that contribute to phenotypic variation.
Subject(s)
Genome, Plant , Molecular Sequence Annotation , Zea mays/genetics , Centromere/genetics , Chromosome Mapping , Chromosomes, Plant , DNA Methylation , Disease Resistance/genetics , Genes, Plant , Genetic Variation , Genotype , High-Throughput Nucleotide Sequencing , Multifactorial Inheritance/genetics , Phenotype , Plant Diseases , Polymorphism, Single Nucleotide , Regulatory Sequences, Nucleic Acid , Sequence Analysis, DNA , Tetraploidy , Transcriptome , Whole Genome SequencingABSTRACT
Improvements in long-read data and scaffolding technologies have enabled rapid generation of reference-quality assemblies for complex genomes. Still, an assessment of critical sequence depth and read length is important for allocating limited resources. To this end, we have generated eight assemblies for the complex genome of the maize inbred line NC358 using PacBio datasets ranging from 20 to 75 × genomic depth and with N50 subread lengths of 11-21 kb. Assemblies with ≤30 × depth and N50 subread length of 11 kb are highly fragmented, with even low-copy genic regions showing degradation at 20 × depth. Distinct sequence-quality thresholds are observed for complete assembly of genes, transposable elements, and highly repetitive genomic features such as telomeres, heterochromatic knobs, and centromeres. In addition, we show high-quality optical maps can dramatically improve contiguity in even our most fragmented base assembly. This study provides a useful resource allocation reference to the community as long-read technologies continue to mature.
Subject(s)
High-Throughput Nucleotide Sequencing/methods , Inbreeding , Zea mays/genetics , Base Sequence , DNA Transposable Elements/genetics , Genome, Plant , Repetitive Sequences, Nucleic Acid/geneticsABSTRACT
Study of domestication is complex but essential to our understanding of evolutionary processes and for crop breeding. A new study analyzes genomic data from 163 lines of domesticated African rice and 83 lines of its wild relative, clarifying the history of African rice domestication.
