In this task, you are given an abstract of article. Your task is to generate title for this article. Preferred titles are under thirty words.

Q: By employing the nuclear DNA of the African rice Oryza glaberrima as a reference genome, the timing, natures, mechanisms, and specificities of recent sequence evolution in the indica and japonica subspecies of Oryza sativa were identified. The data indicate that the genome sizes of both indica and japonica have increased substantially, >2% and >6%, respectively, since their divergence from a common ancestor, mainly because of the amplification of LTR-retrotransposons. However, losses of all classes of DNA sequence through unequal homologous recombination and illegitimate recombination have attenuated the growth of the rice genome. Small deletions have been particularly frequent throughout the genome. In >1 Mb of orthologous regions that we analyzed, no cases of complete gene acquisition or loss from either indica or japonica were found, nor was any example of precise transposon excision detected. The sequences between genes were observed to have a very high rate of divergence, indicating a molecular clock for transposable elements that is at least 2-fold more rapid than synonymous base substitutions within genes. We found that regions prone to frequent insertions and deletions also exhibit higher levels of point mutation. These results indicate a highly dynamic rice genome with competing processes for the generation and removal of genetic variation.

A: Rapid recent growth and divergence of rice nuclear genomes.
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Q: We propose that the microRNA milieu, unique to each cell type, productively dampens the expression of thousands of mRNAs and provides important context for the evolution of all metazoan mRNA sequences. For genes that should not be expressed in a particular cell type, protein output is lowered to inconsequential levels. For other genes, dosage is adjusted in a manner that allows for customized expression in different cell types while achieving a more uniform level within each cell type. In these ways, the microRNAs add an extensive layer of gene control that integrates with transcriptional and other regulatory processes to expand the complexity of metazoan gene expression.

A: Micromanagers of gene expression: the potentially widespread influence of metazoan microRNAs
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Q: Polycomb Group (PcG) proteins mediate heritable gene silencing by modifying chromatin structure. An essential PcG complex, PRC1, compacts chromatin and inhibits chromatin remodeling. In Drosophila melanogaster, the intrinsically disordered C-terminal region of PSC (PSC-CTR) mediates these noncovalent effects on chromatin, and is essential for viability. Because the PSC-CTR sequence is poorly conserved, the significance of its effects on chromatin outside of Drosophila was unclear. The absence of folded domains also made it difficult to understand how the sequence of PSC-CTR encodes its function. To determine the mechanistic basis and extent of conservation of PSC-CTR activity, we identified 17 metazoan PSC-CTRs spanning chordates to arthropods, and examined their sequence features and biochemical properties. PSC-CTR sequences are poorly conserved, but are all highly charged and structurally disordered. We show that active PSC-CTRs--which bind DNA tightly and inhibit chromatin remodeling efficiently--are distinguished from less active ones by the absence of extended negatively charged stretches. PSC-CTR activity can be increased by dispersing its contiguous negative charge, confirming the importance of this property. Using the sequence properties defined as important for PSC-CTR activity, we predicted the presence of active PSC-CTRs in additional diverse genomes. Our analysis reveals broad conservation of PSC-CTR activity across metazoans. This conclusion could not have been determined from sequence alignments. We further find that plants that lack active PSC-CTRs instead possess a functionally analogous PcG protein, EMF1. Thus, our study suggests that a disordered domain with dispersed negative charges underlies PRC1 activity, and is conserved across metazoans and plants.

A:
A core subunit of Polycomb repressive complex 1 is broadly conserved in function but not primary sequence.
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