Diurnal transcriptomics analysis reveals the regulatory role of the circadian rhythm in super-hybrid rice LY2186
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ABSTRACT: Heterosis, an important biological phenomenon wherein F1 hybrids exhibit better performance than any of their parents, has been widely applied; however, its underlying mechanism remains largely unknown. Here, we studied and compared the dynamic transcriptional profiles of super-hybrid rice LY2186 and its parents at 17 time points during 2 day/night cycles and identified 1,552 rhythmic differentially expressed genes (RDGs). Cluster and functional enrichment analyses revealed that the day- and night-phased RDGs were mainly enriched in the photosynthesis and stress response categories, respectively. Regulatory network analysis indicated that circadian-related RDGs are core components in both the day and night phases and extensively regulate downstream genes involved in photosynthesis, starch synthesis, plant hormone signal transduction, and other pathways. Furthermore, among the 282 RDGs mapped onto the quantitative tract loci of small intervals (≤100 genes), 72.3% were significantly enriched in the yield, vigor, and anatomy categories. These findings provide valuable information for exploring heterosis mechanisms further and guiding breeding practices.
Project description:Hybrid plants and animals grow larger and more vigorously than the parents, a common phenomenon known as hybrid vigor or heterosis. Heterosis often correlates with the genetic distance between hybridizing parents, but the mechanism for this is largely unknown. We found that genetic distance was correlated with natural variation of stress responses under the control of the circadian clock. CIRCADIAN-CLOCK-ASSOCIATED1 (CCA1) and LATE-ELONGATED-HYPOCOTYL (LHY) or CCA1 alone mediate expression amplitudes and periods of these stress-responsive genes in stress and non-stress conditions. In Arabidopsis thaliana intraspecific hybrids, genome-wide expression of many biotic and abiotic stress-responsive genes was diurnally repressed to promote biomass heterosis, which is associated with several biomass quantitative trait loci (QTLs). Expression differences in four selected stress-responsive genes among ten ecotypes could be used to predict heterosis in their hybrids. Parent plants with larger expression differences between stress-responsive genes produced higher-vigor hybrids, while those with smaller differences produced lower-vigor hybrids. Stress-responsive genes were epigenetically repressed in the hybrids under normal conditions but induced during times of stress at certain times of the day, balancing the tradeoff between stress responses and growth. Consistently, repressing the stress genes in diploids increased growth vigor. We demonstrate how hybrids manipulate diurnal stress-responsive gene expression to enhance growth vigor. Both circadian and epigenetic regulation play key roles in the altered expression of stress-responsive genes in hybrids. Our findings provide a conceptual advance and mechanistic understanding of heterosis, as well as selection criteria for parents to be effectively used for producing high-yield hybrids.
Project description:Hybrid plants and animals grow larger and more vigorously than the parents, a common phenomenon known as hybrid vigor or heterosis. Heterosis often correlates with the genetic distance between hybridizing parents, but the mechanism for this is largely unknown. We found that genetic distance was correlated with natural variation of stress responses under the control of the circadian clock. CIRCADIAN-CLOCK-ASSOCIATED1 (CCA1) and LATE-ELONGATED-HYPOCOTYL (LHY) or CCA1 alone mediate expression amplitudes and periods of these stress-responsive genes in stress and non-stress conditions. In Arabidopsis thaliana intraspecific hybrids, genome-wide expression of many biotic and abiotic stress-responsive genes was diurnally repressed to promote biomass heterosis, which is associated with several biomass quantitative trait loci (QTLs). Expression differences in four selected stress-responsive genes among ten ecotypes could be used to predict heterosis in their hybrids. Parent plants with larger expression differences between stress-responsive genes produced higher-vigor hybrids, while those with smaller differences produced lower-vigor hybrids. Stress-responsive genes were epigenetically repressed in the hybrids under normal conditions but induced during times of stress at certain times of the day, balancing the tradeoff between stress responses and growth. Consistently, repressing the stress genes in diploids increased growth vigor. We demonstrate how hybrids manipulate diurnal stress-responsive gene expression to enhance growth vigor. Both circadian and epigenetic regulation play key roles in the altered expression of stress-responsive genes in hybrids. Our findings provide a conceptual advance and mechanistic understanding of heterosis, as well as selection criteria for parents to be effectively used for producing high-yield hybrids. Examination of gene expression in Arabidopsis thaliana F1 hybrids between Col and C24 and 3 time points using mRNA-seq
Project description:Heterosis, or hybrid vigor, has been exploited in agriculture to deliver increases in crop yields for over a century, yet the molecular basis is not well understood We have studied the transcriptomes of 15 day old seedlings from intraspecific Arabidopsis hybrids with varying levels of heterosis and their parental lines in order to identify drivers of heterosis. The patterns of altered gene expression in the hybrids point to a reduction in basal defense levels that could reflect the antagonism between plant immunity and plant growth. Associated with this theme are changes to the salicylic acid and auxin regulated networks which are known to control abiotic and biotic defense responses as well as being important regulators of plant growth. Increased auxin response correlates with the heterotic phenotype of greater leaf cell numbers, whereas reduced salicylic acid levels and response promotes increased leaf cell size in hybrids involving C24. By manipulating salicylic acid levels in each of our hybrid systems, we can alter levels of heterosis, promote additional growth in the hybrids, and generate increased growth in the parents, especially C24.
Project description:Heterosis is a fundamental biological phenomenon characterized by the superior performance of a hybrid over its parents in many traits, but the underlying molecular basis remains elusive. To investigate whether DNA methylation plays a role in heterosis, we compared at single base-pair resolution the DNA methylomes of Arabidopsis Ler and C24 parental lines and their reciprocal F1 hybrids that exhibited heterosis for many quantitative traits. Both hybrids displayed increased DNA methylation across their entire genomes, especially in transposable elements. Interestingly, we found that increased methylation of the hybrid genomes predominantly occurred in regions that were differentially methylated in the two parents and covered by small RNAs (sRNAs), implying that the RNA-directed DNA methylation (RdDM) pathway may direct DNA methylation in hybrids. In addition, we found that 77 genes sensitive to remodeling of DNA methylation were transcriptionally repressed in both reciprocal hybrids, including genes involved in flavonoid biosynthesis and two circadian oscillator genes, CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL. Moreover, growth vigor of F1 hybrids was compromised by treatment with an agent that demethylates DNA, and by abolishing production of functional small RNAs due to mutations in Arabidopsis RNA methyltransferase HUA ENHANCER1. Together, our data suggest that genome-wide remodeling of DNA methylation directed by the RdDM pathway may play a role in hybrid vigor. Examination of small RNA sequencing in 2 Arabidopsis ecotypes and their reciprocal hybrids.
Project description:Heterosis is a fundamental biological phenomenon characterized by the superior performance of a hybrid over its parents in many traits, but the underlying molecular basis remains elusive. To investigate whether DNA methylation plays a role in heterosis, we compared at single base-pair resolution the DNA methylomes of Arabidopsis Ler and C24 parental lines and their reciprocal F1 hybrids that exhibited heterosis for many quantitative traits. Both hybrids displayed increased DNA methylation across their entire genomes, especially in transposable elements. Interestingly, we found that increased methylation of the hybrid genomes predominantly occurred in regions that were differentially methylated in the two parents and covered by small RNAs (sRNAs), implying that the RNA-directed DNA methylation (RdDM) pathway may direct DNA methylation in hybrids. In addition, we found that 77 genes sensitive to remodeling of DNA methylation were transcriptionally repressed in both reciprocal hybrids, including genes involved in flavonoid biosynthesis and two circadian oscillator genes, CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL. Moreover, growth vigor of F1 hybrids was compromised by treatment with an agent that demethylates DNA, and by abolishing production of functional small RNAs due to mutations in Arabidopsis RNA methyltransferase HUA ENHANCER1. Together, our data suggest that genome-wide remodeling of DNA methylation directed by the RdDM pathway may play a role in hybrid vigor. Examination of mRNA sequencing in 2 Arabidopsis ecotypes and their reciprocal hybrids.
Project description:In order to circumvent environmental changes throughout fruit development, young and ripening berries were sampled simultaneously on continuously flowering microvines acclimated to controlled circadian light and temperature changes. Gene expression profiles along fruit development were monitored during both day and night with whole genome microarray Nimbelgen® vitis 12x, yielding a total number of 9273 developmentally modulated probesets. All day-detected transcripts were modulated at night, whereas 1755 genes were night-specific. Very similar developmental patterns of gene expression were observed upon independent hierarchical clustering of day and night data, whereas functional categories of allocated transcripts varied according to time of the day. Many transcripts within pathways, known to be upregulated during ripening, in particular those linked to secondary metabolism exhibited a clearer developmental regulation at night than during the day. Functional enrichment analysis also indicated that diurnally modulated genes considerably varied during fruit development, with a shift from cellular organization and photosynthesis in green berries to secondary metabolism and stress-related genes in ripening ones. These results reveal critical changes in gene expression during night development that differ from day development which have not been observed in other transcriptomic studies on fruit development so far.
Project description:Heterosis is a fundamental biological phenomenon characterized by the superior performance of a hybrid over its parents in many traits, but the underlying molecular basis remains elusive. To investigate whether DNA methylation plays a role in heterosis, we compared at single base-pair resolution the DNA methylomes of Arabidopsis Ler and C24 parental lines and their reciprocal F1 hybrids that exhibited heterosis for many quantitative traits. Both hybrids displayed increased DNA methylation across their entire genomes, especially in transposable elements. Interestingly, we found that increased methylation of the hybrid genomes predominantly occurred in regions that were differentially methylated in the two parents and covered by small RNAs (sRNAs), implying that the RNA-directed DNA methylation (RdDM) pathway may direct DNA methylation in hybrids. In addition, we found that 77 genes sensitive to remodeling of DNA methylation were transcriptionally repressed in both reciprocal hybrids, including genes involved in flavonoid biosynthesis and two circadian oscillator genes, CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL. Moreover, growth vigor of F1 hybrids was compromised by treatment with an agent that demethylates DNA, and by abolishing production of functional small RNAs due to mutations in Arabidopsis RNA methyltransferase HUA ENHANCER1. Together, our data suggest that genome-wide remodeling of DNA methylation directed by the RdDM pathway may play a role in hybrid vigor. Examination of DNA methylation by Bisulfite sequencing in 2 Arabidopsis ecotypes and their reciprocal hybrids.
Project description:Heterosis is a fundamental biological phenomenon characterized by the superior performance of a hybrid over its parents in many traits, but the underlying molecular basis remains elusive. To investigate whether DNA methylation plays a role in heterosis, we compared at single base-pair resolution the DNA methylomes of Arabidopsis Ler and C24 parental lines and their reciprocal F1 hybrids that exhibited heterosis for many quantitative traits. Both hybrids displayed increased DNA methylation across their entire genomes, especially in transposable elements. Interestingly, we found that increased methylation of the hybrid genomes predominantly occurred in regions that were differentially methylated in the two parents and covered by small RNAs (sRNAs), implying that the RNA-directed DNA methylation (RdDM) pathway may direct DNA methylation in hybrids. In addition, we found that 77 genes sensitive to remodeling of DNA methylation were transcriptionally repressed in both reciprocal hybrids, including genes involved in flavonoid biosynthesis and two circadian oscillator genes, CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL. Moreover, growth vigor of F1 hybrids was compromised by treatment with an agent that demethylates DNA, and by abolishing production of functional small RNAs due to mutations in Arabidopsis RNA methyltransferase HUA ENHANCER1. Together, our data suggest that genome-wide remodeling of DNA methylation directed by the RdDM pathway may play a role in hybrid vigor.
Project description:Heterosis is a fundamental biological phenomenon characterized by the superior performance of a hybrid over its parents in many traits, but the underlying molecular basis remains elusive. To investigate whether DNA methylation plays a role in heterosis, we compared at single base-pair resolution the DNA methylomes of Arabidopsis Ler and C24 parental lines and their reciprocal F1 hybrids that exhibited heterosis for many quantitative traits. Both hybrids displayed increased DNA methylation across their entire genomes, especially in transposable elements. Interestingly, we found that increased methylation of the hybrid genomes predominantly occurred in regions that were differentially methylated in the two parents and covered by small RNAs (sRNAs), implying that the RNA-directed DNA methylation (RdDM) pathway may direct DNA methylation in hybrids. In addition, we found that 77 genes sensitive to remodeling of DNA methylation were transcriptionally repressed in both reciprocal hybrids, including genes involved in flavonoid biosynthesis and two circadian oscillator genes, CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL. Moreover, growth vigor of F1 hybrids was compromised by treatment with an agent that demethylates DNA, and by abolishing production of functional small RNAs due to mutations in Arabidopsis RNA methyltransferase HUA ENHANCER1. Together, our data suggest that genome-wide remodeling of DNA methylation directed by the RdDM pathway may play a role in hybrid vigor.
Project description:Heterosis is a fundamental biological phenomenon characterized by the superior performance of a hybrid over its parents in many traits, but the underlying molecular basis remains elusive. To investigate whether DNA methylation plays a role in heterosis, we compared at single base-pair resolution the DNA methylomes of Arabidopsis Ler and C24 parental lines and their reciprocal F1 hybrids that exhibited heterosis for many quantitative traits. Both hybrids displayed increased DNA methylation across their entire genomes, especially in transposable elements. Interestingly, we found that increased methylation of the hybrid genomes predominantly occurred in regions that were differentially methylated in the two parents and covered by small RNAs (sRNAs), implying that the RNA-directed DNA methylation (RdDM) pathway may direct DNA methylation in hybrids. In addition, we found that 77 genes sensitive to remodeling of DNA methylation were transcriptionally repressed in both reciprocal hybrids, including genes involved in flavonoid biosynthesis and two circadian oscillator genes, CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL. Moreover, growth vigor of F1 hybrids was compromised by treatment with an agent that demethylates DNA, and by abolishing production of functional small RNAs due to mutations in Arabidopsis RNA methyltransferase HUA ENHANCER1. Together, our data suggest that genome-wide remodeling of DNA methylation directed by the RdDM pathway may play a role in hybrid vigor.