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Gene expression analyses in maize inbreds and hybrids with varying levels of heterosis.

Stupar RM, Gardiner JM, Oldre AG, Haun WJ, Chandler VL, Springer NM - BMC Plant Biol. (2008)

Bottom Line: We have found that maize inbred genetic diversity is correlated with transcriptional variation.These findings suggest that heterosis is probably not a consequence of higher levels of additive or non-additive expression, but may be related to transcriptional variation between parents.The lack of correlation between better parent heterosis levels for different traits suggests that transcriptional diversity at specific sets of genes may influence heterosis for different traits.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Plant and Microbial Genomics, Department of Plant Biology, University of Minnesota, Saint Paul MN 55108, USA. stup0004@umn.edu

ABSTRACT

Background: Heterosis is the superior performance of F1 hybrid progeny relative to the parental phenotypes. Maize exhibits heterosis for a wide range of traits, however the magnitude of heterosis is highly variable depending on the choice of parents and the trait(s) measured. We have used expression profiling to determine whether the level, or types, of non-additive gene expression vary in maize hybrids with different levels of genetic diversity or heterosis.

Results: We observed that the distributions of better parent heterosis among a series of 25 maize hybrids generally do not exhibit significant correlations between different traits. Expression profiling analyses for six of these hybrids, chosen to represent diversity in genotypes and heterosis responses, revealed a correlation between genetic diversity and transcriptional variation. The majority of differentially expressed genes in each of the six different hybrids exhibited additive expression patterns, and approximately 25% exhibited statistically significant non-additive expression profiles. Among the non-additive profiles, approximately 80% exhibited hybrid expression levels between the parental levels, approximately 20% exhibited hybrid expression levels at the parental levels and ~1% exhibited hybrid levels outside the parental range.

Conclusion: We have found that maize inbred genetic diversity is correlated with transcriptional variation. However, sampling of seedling tissues indicated that the frequencies of additive and non-additive expression patterns are very similar across a range of hybrid lines. These findings suggest that heterosis is probably not a consequence of higher levels of additive or non-additive expression, but may be related to transcriptional variation between parents. The lack of correlation between better parent heterosis levels for different traits suggests that transcriptional diversity at specific sets of genes may influence heterosis for different traits.

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Relationship between parental genetic diversity and hybrid heterosis among traits and hybrids. The percentage better parent heterosis (BPH) for each hybrid is plotted against the genetic distance between parents. The 25 hybrids were scored based on percentage BPH for five traits (plant final height, days to flowering, weight of 50 seeds, 11-day height and 11-day biomass). Traits measured on field-grown plants are shown in (A) and traits measured on greenhouse-grown plants are shown in (B). Average percent BPH is shown based on two field replicates (A) and three greenhouse replicates (B). Spots representing crosses between stiff stalk (SS) and non-stiff stalk (NSS) groups are shown in red, and spots representing crosses within either group are shown in blue. The Pearson's R correlation value and p-value of the regression are shown for each trait. The six hybrids that were used for expression profiling are labelled in each of the five plots.
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Figure 3: Relationship between parental genetic diversity and hybrid heterosis among traits and hybrids. The percentage better parent heterosis (BPH) for each hybrid is plotted against the genetic distance between parents. The 25 hybrids were scored based on percentage BPH for five traits (plant final height, days to flowering, weight of 50 seeds, 11-day height and 11-day biomass). Traits measured on field-grown plants are shown in (A) and traits measured on greenhouse-grown plants are shown in (B). Average percent BPH is shown based on two field replicates (A) and three greenhouse replicates (B). Spots representing crosses between stiff stalk (SS) and non-stiff stalk (NSS) groups are shown in red, and spots representing crosses within either group are shown in blue. The Pearson's R correlation value and p-value of the regression are shown for each trait. The six hybrids that were used for expression profiling are labelled in each of the five plots.

Mentions: We assessed whether the concept of heterotic groups, which was developed as a tool to enable breeding for grain yield [4], would predict heterosis levels for other traits. The concept of heterotic groups predicts that crosses within a heterotic group will generally exhibit less heterosis than crosses between heterotic groups. For all five traits we monitored, there were multiple intra-heterotic group crosses that exhibited higher levels of heterosis than several of the inter-heterotic group hybrids. For example, while B37 × B73 is an intra-heterotic group cross it displayed heterosis levels among traits that were similar to, and sometimes superior to, inter-heterotic group hybrids made between more distant parental genotypes (Figure 2, 3). It is worth noting that heterotic groups are not entirely defined based upon heterosis but are often influenced by relatedness and other factors [4].


Gene expression analyses in maize inbreds and hybrids with varying levels of heterosis.

Stupar RM, Gardiner JM, Oldre AG, Haun WJ, Chandler VL, Springer NM - BMC Plant Biol. (2008)

Relationship between parental genetic diversity and hybrid heterosis among traits and hybrids. The percentage better parent heterosis (BPH) for each hybrid is plotted against the genetic distance between parents. The 25 hybrids were scored based on percentage BPH for five traits (plant final height, days to flowering, weight of 50 seeds, 11-day height and 11-day biomass). Traits measured on field-grown plants are shown in (A) and traits measured on greenhouse-grown plants are shown in (B). Average percent BPH is shown based on two field replicates (A) and three greenhouse replicates (B). Spots representing crosses between stiff stalk (SS) and non-stiff stalk (NSS) groups are shown in red, and spots representing crosses within either group are shown in blue. The Pearson's R correlation value and p-value of the regression are shown for each trait. The six hybrids that were used for expression profiling are labelled in each of the five plots.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2365949&req=5

Figure 3: Relationship between parental genetic diversity and hybrid heterosis among traits and hybrids. The percentage better parent heterosis (BPH) for each hybrid is plotted against the genetic distance between parents. The 25 hybrids were scored based on percentage BPH for five traits (plant final height, days to flowering, weight of 50 seeds, 11-day height and 11-day biomass). Traits measured on field-grown plants are shown in (A) and traits measured on greenhouse-grown plants are shown in (B). Average percent BPH is shown based on two field replicates (A) and three greenhouse replicates (B). Spots representing crosses between stiff stalk (SS) and non-stiff stalk (NSS) groups are shown in red, and spots representing crosses within either group are shown in blue. The Pearson's R correlation value and p-value of the regression are shown for each trait. The six hybrids that were used for expression profiling are labelled in each of the five plots.
Mentions: We assessed whether the concept of heterotic groups, which was developed as a tool to enable breeding for grain yield [4], would predict heterosis levels for other traits. The concept of heterotic groups predicts that crosses within a heterotic group will generally exhibit less heterosis than crosses between heterotic groups. For all five traits we monitored, there were multiple intra-heterotic group crosses that exhibited higher levels of heterosis than several of the inter-heterotic group hybrids. For example, while B37 × B73 is an intra-heterotic group cross it displayed heterosis levels among traits that were similar to, and sometimes superior to, inter-heterotic group hybrids made between more distant parental genotypes (Figure 2, 3). It is worth noting that heterotic groups are not entirely defined based upon heterosis but are often influenced by relatedness and other factors [4].

Bottom Line: We have found that maize inbred genetic diversity is correlated with transcriptional variation.These findings suggest that heterosis is probably not a consequence of higher levels of additive or non-additive expression, but may be related to transcriptional variation between parents.The lack of correlation between better parent heterosis levels for different traits suggests that transcriptional diversity at specific sets of genes may influence heterosis for different traits.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Plant and Microbial Genomics, Department of Plant Biology, University of Minnesota, Saint Paul MN 55108, USA. stup0004@umn.edu

ABSTRACT

Background: Heterosis is the superior performance of F1 hybrid progeny relative to the parental phenotypes. Maize exhibits heterosis for a wide range of traits, however the magnitude of heterosis is highly variable depending on the choice of parents and the trait(s) measured. We have used expression profiling to determine whether the level, or types, of non-additive gene expression vary in maize hybrids with different levels of genetic diversity or heterosis.

Results: We observed that the distributions of better parent heterosis among a series of 25 maize hybrids generally do not exhibit significant correlations between different traits. Expression profiling analyses for six of these hybrids, chosen to represent diversity in genotypes and heterosis responses, revealed a correlation between genetic diversity and transcriptional variation. The majority of differentially expressed genes in each of the six different hybrids exhibited additive expression patterns, and approximately 25% exhibited statistically significant non-additive expression profiles. Among the non-additive profiles, approximately 80% exhibited hybrid expression levels between the parental levels, approximately 20% exhibited hybrid expression levels at the parental levels and ~1% exhibited hybrid levels outside the parental range.

Conclusion: We have found that maize inbred genetic diversity is correlated with transcriptional variation. However, sampling of seedling tissues indicated that the frequencies of additive and non-additive expression patterns are very similar across a range of hybrid lines. These findings suggest that heterosis is probably not a consequence of higher levels of additive or non-additive expression, but may be related to transcriptional variation between parents. The lack of correlation between better parent heterosis levels for different traits suggests that transcriptional diversity at specific sets of genes may influence heterosis for different traits.

Show MeSH
Related in: MedlinePlus