Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA.
Proc Natl Acad Sci U S A. 2012 Jun 26;109(26):10444-9. doi: 10.1073/pnas.1202073109. Epub 2012 Jun 11.
Small RNAs (sRNAs) are hypothesized to contribute to hybrid vigor because they maintain genome integrity, contribute to genetic diversity, and control gene expression. We used Illumina sequencing to assess how sRNA populations vary between two maize inbred lines (B73 and Mo17) and their hybrid. We sampled sRNAs from the seedling shoot apex and the developing ear, two rapidly growing tissues that program the greater growth of maize hybrids. We found that parental differences in siRNAs primarily originate from repeat regions. Although the maize genome contains greater number and complexity of repeats compared with Arabidopsis or rice, we confirmed that, like these simpler plant genomes, 24-nt siRNAs whose abundance differs between maize parents also show a trend of down-regulation following hybridization. Surprisingly, hybrid vigor is fully maintained when 24-nt siRNAs are globally reduced by mutation of the RNA-dependent RNA polymerase 2 encoded by modifier of paramutation1 (mop1). We also discovered that 21-22-nt siRNAs derived from a number of distinct retrotransposon families differentially accumulate between B73 and Mo17 as well as their hybrid. Thus, maize possesses a unique source of genetic variation for regulating transposons and genes at a genomic scale, which may contribute to its high degree of observed heterosis.
小 RNA（sRNAs）被认为有助于杂种优势，因为它们可以维持基因组完整性、促进遗传多样性和控制基因表达。我们使用 Illumina 测序来评估两个玉米自交系（B73 和 Mo17）及其杂种之间 sRNA 群体的变化。我们从幼苗茎尖和发育中的耳朵中采样 sRNA，这两个快速生长的组织程序控制玉米杂种的更大生长。我们发现，siRNAs 的亲本差异主要源自重复区域。尽管与拟南芥或水稻相比，玉米基因组包含更多数量和更复杂的重复，但我们证实，与这些更简单的植物基因组一样，在玉米亲本之间丰度不同的 24-nt siRNAs 在杂交后也表现出下调的趋势。令人惊讶的是，当突变 RNA 依赖的 RNA 聚合酶 2 编码的修饰体突变 1（mop1）导致 24-nt siRNAs 全局减少时，杂种优势仍能完全维持。我们还发现，源自许多不同反转录转座子家族的 21-22-nt siRNAs 在 B73 和 Mo17 及其杂种之间也有差异积累。因此，玉米在调节转座子和基因方面具有独特的遗传变异来源，这可能有助于其表现出高度的杂种优势。
