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Imprinting in plants as a mechanism to generate seed phenotypic diversity.

Bai F, Settles AM - Front Plant Sci (2015)

Bottom Line: There is significant evidence for transposable elements and repeat sequences near genes acting as cis-elements to determine imprinting status of a gene, implying that imprinted gene expression patterns may evolve randomly and at high frequency.These data are not fully explained by current models for the evolution of imprinting in plant seeds.We suggest that imprinting may have evolved to provide a mechanism for rapid neofunctionalization of genes during seed development to increase phenotypic diversity of seeds.

View Article: PubMed Central - PubMed

Affiliation: Horticultural Sciences Department and Plant Molecular and Cellular Biology Program, University of Florida Gainesville, FL, USA.

ABSTRACT
Normal plant development requires epigenetic regulation to enforce changes in developmental fate. Genomic imprinting is a type of epigenetic regulation in which identical alleles of genes are expressed in a parent-of-origin dependent manner. Deep sequencing of transcriptomes has identified hundreds of imprinted genes with scarce evidence for the developmental importance of individual imprinted loci. Imprinting is regulated through global DNA demethylation in the central cell prior to fertilization and directed repression of individual loci with the Polycomb Repressive Complex 2 (PRC2). There is significant evidence for transposable elements and repeat sequences near genes acting as cis-elements to determine imprinting status of a gene, implying that imprinted gene expression patterns may evolve randomly and at high frequency. Detailed genetic analysis of a few imprinted loci suggests an imprinted pattern of gene expression is often dispensable for seed development. Few genes show conserved imprinted expression within or between plant species. These data are not fully explained by current models for the evolution of imprinting in plant seeds. We suggest that imprinting may have evolved to provide a mechanism for rapid neofunctionalization of genes during seed development to increase phenotypic diversity of seeds.

No MeSH data available.


Comparison of Mendelian genetic inheritance and imprinted inheritance. (A) The a1 locus shows Mendelian inheritance in self-pollinations of A1/a1 individuals. Full purple color kernels are dominant over yellow kernels and the progeny segregate in a 3:1 ratio. (B) The Rr allele shows imprinted inheritance. Self-pollination of Rr/r yields three kernel color types in a 2:1:1 ratio of purple to mottled to yellow kernels. Purple kernels inherited the Rr allele from the megagametophyte. Mottled kernels are heterozygous individuals that inherited the Rr allele from the pollen. Kernel counts are given for the ears shown in the upper panels.
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Figure 2: Comparison of Mendelian genetic inheritance and imprinted inheritance. (A) The a1 locus shows Mendelian inheritance in self-pollinations of A1/a1 individuals. Full purple color kernels are dominant over yellow kernels and the progeny segregate in a 3:1 ratio. (B) The Rr allele shows imprinted inheritance. Self-pollination of Rr/r yields three kernel color types in a 2:1:1 ratio of purple to mottled to yellow kernels. Purple kernels inherited the Rr allele from the megagametophyte. Mottled kernels are heterozygous individuals that inherited the Rr allele from the pollen. Kernel counts are given for the ears shown in the upper panels.

Mentions: It is easiest to understand imprinted inheritance through an example. The A1 locus of maize encodes a structural gene for anthocyanin biosynthesis (O’Reilly et al., 1985), while the R locus encodes a transcription factor that induces anthocyanin biosynthesis (Ludwig et al., 1989; Perrot and Cone, 1989). The A1 locus shows Mendelian inheritance, while certain haplotypes of the R locus are imprinted (Kermicle, 1969). Indeed, R was the first imprinted locus described in plants. The Rr allele shows altered expression when Rr is inherited from pollen. The expression pattern of paternally inherited Rr can be seen by contrasting self-pollinations of heterozygous individuals for A1/a1 or Rr/r (Figure 2). When a plant heterozygous for A1/a1 is self-pollinated, the seeds segregate in a 3:1 ratio for full color to yellow kernels (Figure 2). Self-pollination of Rr/r yields three kernel color types in a 2:1:1 ratio of purple to yellow to mottled purple kernels. These mottled purple kernels have an endosperm genotype of r r/Rr where the dominant allele inherited from the male is repressed in a stochastic pattern in the seed. The same paternal Rr allele is not affected in the embryo and plants from mottled kernels will yield full color kernels if crossed as female to an r/r plant and mottled kernels if crossed as a male to the r/r genotype.


Imprinting in plants as a mechanism to generate seed phenotypic diversity.

Bai F, Settles AM - Front Plant Sci (2015)

Comparison of Mendelian genetic inheritance and imprinted inheritance. (A) The a1 locus shows Mendelian inheritance in self-pollinations of A1/a1 individuals. Full purple color kernels are dominant over yellow kernels and the progeny segregate in a 3:1 ratio. (B) The Rr allele shows imprinted inheritance. Self-pollination of Rr/r yields three kernel color types in a 2:1:1 ratio of purple to mottled to yellow kernels. Purple kernels inherited the Rr allele from the megagametophyte. Mottled kernels are heterozygous individuals that inherited the Rr allele from the pollen. Kernel counts are given for the ears shown in the upper panels.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4307191&req=5

Figure 2: Comparison of Mendelian genetic inheritance and imprinted inheritance. (A) The a1 locus shows Mendelian inheritance in self-pollinations of A1/a1 individuals. Full purple color kernels are dominant over yellow kernels and the progeny segregate in a 3:1 ratio. (B) The Rr allele shows imprinted inheritance. Self-pollination of Rr/r yields three kernel color types in a 2:1:1 ratio of purple to mottled to yellow kernels. Purple kernels inherited the Rr allele from the megagametophyte. Mottled kernels are heterozygous individuals that inherited the Rr allele from the pollen. Kernel counts are given for the ears shown in the upper panels.
Mentions: It is easiest to understand imprinted inheritance through an example. The A1 locus of maize encodes a structural gene for anthocyanin biosynthesis (O’Reilly et al., 1985), while the R locus encodes a transcription factor that induces anthocyanin biosynthesis (Ludwig et al., 1989; Perrot and Cone, 1989). The A1 locus shows Mendelian inheritance, while certain haplotypes of the R locus are imprinted (Kermicle, 1969). Indeed, R was the first imprinted locus described in plants. The Rr allele shows altered expression when Rr is inherited from pollen. The expression pattern of paternally inherited Rr can be seen by contrasting self-pollinations of heterozygous individuals for A1/a1 or Rr/r (Figure 2). When a plant heterozygous for A1/a1 is self-pollinated, the seeds segregate in a 3:1 ratio for full color to yellow kernels (Figure 2). Self-pollination of Rr/r yields three kernel color types in a 2:1:1 ratio of purple to yellow to mottled purple kernels. These mottled purple kernels have an endosperm genotype of r r/Rr where the dominant allele inherited from the male is repressed in a stochastic pattern in the seed. The same paternal Rr allele is not affected in the embryo and plants from mottled kernels will yield full color kernels if crossed as female to an r/r plant and mottled kernels if crossed as a male to the r/r genotype.

Bottom Line: There is significant evidence for transposable elements and repeat sequences near genes acting as cis-elements to determine imprinting status of a gene, implying that imprinted gene expression patterns may evolve randomly and at high frequency.These data are not fully explained by current models for the evolution of imprinting in plant seeds.We suggest that imprinting may have evolved to provide a mechanism for rapid neofunctionalization of genes during seed development to increase phenotypic diversity of seeds.

View Article: PubMed Central - PubMed

Affiliation: Horticultural Sciences Department and Plant Molecular and Cellular Biology Program, University of Florida Gainesville, FL, USA.

ABSTRACT
Normal plant development requires epigenetic regulation to enforce changes in developmental fate. Genomic imprinting is a type of epigenetic regulation in which identical alleles of genes are expressed in a parent-of-origin dependent manner. Deep sequencing of transcriptomes has identified hundreds of imprinted genes with scarce evidence for the developmental importance of individual imprinted loci. Imprinting is regulated through global DNA demethylation in the central cell prior to fertilization and directed repression of individual loci with the Polycomb Repressive Complex 2 (PRC2). There is significant evidence for transposable elements and repeat sequences near genes acting as cis-elements to determine imprinting status of a gene, implying that imprinted gene expression patterns may evolve randomly and at high frequency. Detailed genetic analysis of a few imprinted loci suggests an imprinted pattern of gene expression is often dispensable for seed development. Few genes show conserved imprinted expression within or between plant species. These data are not fully explained by current models for the evolution of imprinting in plant seeds. We suggest that imprinting may have evolved to provide a mechanism for rapid neofunctionalization of genes during seed development to increase phenotypic diversity of seeds.

No MeSH data available.