Project description:Heterosis is most frequently manifested by the substantially increased vigorous growth of hybrids compared with their parents. Investigating genomic variations in natural populations is essential to understand the initial molecular mechanisms underlying heterosis in plants. Here, we characterized the genomic architecture associated with biomass heterosis in 200 Arabidopsis hybrids. The genome-wide heterozygosity of hybrids makes a limited contribution to biomass heterosis, and no locus shows an obvious overdominance effect in hybrids. However, the accumulation of significant genetic loci identified in genome wide association studies (GWAS) in hybrids strongly correlates with better-parent heterosis (BPH). Candidate genes for biomass BPH fall into diverse biological functions, including cellular, metabolic, and developmental processes and stimulus-responsive pathways. Important heterosis candidates include WUSCHEL, ARGOS, and some genes that encode key factors involved in cell cycle regulation. Interestingly, transcriptomic analyses in representative Arabidopsis hybrid combinations reveal that heterosis candidate genes are functionally enriched in stimulus-responsive pathways, including responses to biotic and abiotic stimuli and immune responses. In addition, stimulus-responsive genes are repressed to low-parent levels in hybrids with high BPH, whereas middle-parent expression patterns are exhibited in hybrids with no BPH. Our study reveals a genomic architecture for understanding the molecular mechanisms of biomass heterosis in Arabidopsis, in which the accumulation of the superior alleles of genes involved in metabolic and cellular processes improve the development and growth of hybrids, whereas the overall repressed expression of stimulus responsive genes prioritizes growth over responding to environmental stimuli in hybrids under normal conditions.
Project description:Heterosis is most frequently manifested by the substantially increased vigorous growth of hybrids compared with their parents. Investigating genomic variations in natural populations is essential to understand the initial molecular mechanisms underlying heterosis in plants. Here, we characterized the genomic architecture associated with biomass heterosis in 200 Arabidopsis hybrids. The genome-wide heterozygosity of hybrids makes a limited contribution to biomass heterosis, and no locus shows an obvious overdominance effect in hybrids. However, the accumulation of significant genetic loci identified in genome wide association studies (GWAS) in hybrids strongly correlates with better-parent heterosis (BPH). Candidate genes for biomass BPH fall into diverse biological functions, including cellular, metabolic, and developmental processes and stimulus-responsive pathways. Important heterosis candidates include WUSCHEL, ARGOS, and some genes that encode key factors involved in cell cycle regulation. Interestingly, transcriptomic analyses in representative Arabidopsis hybrid combinations reveal that heterosis candidate genes are functionally enriched in stimulus-responsive pathways, including responses to biotic and abiotic stimuli and immune responses. In addition, stimulus-responsive genes are repressed to low-parent levels in hybrids with high BPH, whereas middle-parent expression patterns are exhibited in hybrids with no BPH. Our study reveals a genomic architecture for understanding the molecular mechanisms of biomass heterosis in Arabidopsis, in which the accumulation of the superior alleles of genes involved in metabolic and cellular processes improve the development and growth of hybrids, whereas the overall repressed expression of stimulus responsive genes prioritizes growth over responding to environmental stimuli in hybrids under normal conditions.
Project description:Transcriptional profiling of A. thaliana seedlings (early development) at 7 time points We investigate biomass heterosis by scoring partial correlations of transcriptional profiles.
Project description:Many animal and plant species exhibit increased growth rates, reach larger sizes and, in the cases of crops and farm animals, produce higher yields when bred as hybrids between genetically differing strains, a phenomenon known as hybrid vigour or heterosis. Despite the importance of heterosis, and its extensive genetic analysis, there has been little understanding of its molecular basis. We aimed to determine whether characteristics of the leaf transcriptome, as an indicator of the innate functional genetic architecture of a plant line, could be used as markers to predict heterosis and the performance of hybrids, a methodology we term Association Transcriptomics. Relationships between transcript abundance of specific genes and the values of heterosis and heterosis-dependent traits were identified and mathematical models were constructed that relate gene expression characteristics in inbred lines of Arabidopsis thaliana and maize with vegetative biomass and for grain yield, respectively, in corresponding hybrids.
Project description:Heterosis occurs where F1 offspring display superior characteristics to the parents. Heterosis is usually considered to result from crosses of genetically distinct (e.g. homozygous inbred) parents producing heterozygous F1 offspring. Most mechanistic models for heterosis require genetically heterozygous F1 hybrid offspring harbouring allelic diversity. Epigenetic or dosage models for heterosis could allow for heterosis effects in F1 offspring that display no allelic diversity with their parents. Reciprocal inter-ploidy crosses between diploid (2x) and tetraploid (4x) lines in the same genetic background generates genetically identical F1 triploids (3x). Such reciprocal F1 triploids differ according to whether the additional chromosome set is either maternally (maternal excess) or paternally inherited (paternal excess). Biomass accumulation and abiotic stress tolerance between the parental (2x and 4x) and reciprocal F1 triploid (3x) offspring of Arabidopsis thaliana accession C24 reveals a strong parental genome-dosage induced heterosis in the paternal-excess triploid F1 plants. In these F1 triploids, the circadian clock related genes CCA1 and TOC1, and the growth factors PIF4 and PIF5, display different expression levels compared to the non-heterotic maternal excess F1 triploid siblings. Whole transcriptome profiling reveals a paternal genome dosage effect on gene expression levels with strong enrichment for dysregulated abiotic stress-related genes in the paternal excess F1 triploids. This study demonstrates that heterosis can be triggered without allelic diversity in F1 triploid plants. Heterosis without heterozygosity in plants can be induced via an epigenetic “chromosome imprinting” like parental genome dosage effect requiring paternal transmission of an additional chromosome set
Project description:Heterosis occurs where F1 offspring display superior characteristics to the parents. Heterosis is usually considered to result from crosses of genetically distinct (e.g. homozygous inbred) parents producing heterozygous F1 offspring. Most mechanistic models for heterosis require genetically heterozygous F1 hybrid offspring harbouring allelic diversity. Epigenetic or dosage models for heterosis could allow for heterosis effects in F1 offspring that display no allelic diversity with their parents. Reciprocal inter-ploidy crosses between diploid (2x) and tetraploid (4x) lines in the same genetic background generates genetically identical F1 triploids (3x). Such reciprocal F1 triploids differ according to whether the additional chromosome set is either maternally (maternal excess) or paternally inherited (paternal excess). Biomass accumulation and abiotic stress tolerance between the parental (2x and 4x) and reciprocal F1 triploid (3x) offspring of Arabidopsis thaliana accession C24 reveals a strong parental genome-dosage induced heterosis in the paternal-excess triploid F1 plants. In these F1 triploids, the circadian clock related genes CCA1 and TOC1, and the growth factors PIF4 and PIF5, display different expression levels compared to the non-heterotic maternal excess F1 triploid siblings. Whole transcriptome profiling reveals a paternal genome dosage effect on gene expression levels with strong enrichment for dysregulated abiotic stress-related genes in the paternal excess F1 triploids. This study demonstrates that heterosis can be triggered without allelic diversity in F1 triploid plants. Heterosis without heterozygosity in plants can be induced via an epigenetic “chromosome imprinting” like parental genome dosage effect requiring paternal transmission of an additional chromosome set 4 or 5 biological replicates per ploidy level, each replicate being a single two weeks old seedling
Project description:Transcriptional profiling of A. thaliana seedlings (early development) at 7 time points We investigate biomass heterosis by scoring partial correlations of transcriptional profiles. We compare 4 genotypes: Col-0 (homozygous parental line), C24 (homozygous parental line), Col-0xC24 and C24xCol-0 (crossings) using 2-4 replicates each
Project description:Hybrid breeding is of economic importance in agriculture for increasing yield, yet the basis of the heterosis is not well understood. In Arabidopsis, crosses between different accessions produce hybrids with varied levels of heterosis relative to parental phenotypes in biomass. In all hybrids the advantages of the F1 hybrid is lost in the F2 for both phenotypic uniformity and yield gain. Success in generating F5/F6 Hybrid Mimic from the cross between C24 and Landsberg erecta (Ler) demonstrated that the large plant phenotype of the F1 hybrids can be stabilized. Hybrid Mimics selection was applied to Wassilewskija (Ws)/Ler and Col/Ler hybrids. The two hybrids showing different levels of heterosis. At 30 DAS, the Col/Ler hybrid generated Hybrid Mimics with rosette diameter and fresh weight equivalent to the F1 hybrid; Ws/Ler Hybrid Mimics outperformed the F1 hybrids in both the rosette size and biomass. Transcriptome analysis revealed up-regulation of cell wall biosynthesis and expansion genes could be a common pathway in increased size in Arabidopsis hybrids and Hybrid Mimics. Intercross of two independent Hybrid Mimic lines can further increase the biomass gain. Our results encourage the use of Hybrid Mimics for breeding and for investigating the molecular basis of heterosis.
Project description:Many animal and plant species exhibit increased growth rates, reach larger sizes and, in the cases of crops and farm animals, produce higher yields when bred as hybrids between genetically differing strains, a phenomenon known as hybrid vigour or heterosis. Despite the importance of heterosis, and its extensive genetic analysis, there has been little understanding of its molecular basis. We aimed to determine whether characteristics of the leaf transcriptome, as an indicator of the innate functional genetic architecture of a plant line, could be used as markers to predict heterosis and the performance of hybrids, a methodology we term Association Transcriptomics. Relationships between transcript abundance of specific genes and the values of heterosis and heterosis-dependent traits were identified and mathematical models were constructed that relate gene expression characteristics in inbred lines of Arabidopsis thaliana and maize with vegetative biomass and for grain yield, respectively, in corresponding hybrids. Plants used for transcriptome analysis were grown from seeds for 2 weeks. Aerial parts above the coleoptiles were excised, weighed and frozen in liquid nitrogen. All plants were harvested as close as practicable to the middle of the photoperiod. Plants used for transcriptome analysis were grown from seeds for 2 weeks. Maize seeds were first imbibed in distilled water for 2 days in glasshouse conditions to break dormancy, before transfer to peat and sand P7 pots. They were grown in long day glass house conditions (16 hours photoperiod) at 22 degrees Celsius. Aerial parts above the coleoptiles were excised, weighed and frozen in liquid nitrogen. All plants were harvested as close as practicable to the middle of the photoperiod. Plants for yield trials were grown in the field at Clayton, NC, U.S.A. in 2005. Forty plants of each hybrid were grown in duplicate 0.0007 hectare plots.