Chromosomal distribution of siRNA loci and imprinted genes on maize genome. Lane group a: Chromosomal distribution of siRNA reads abundance. These four lanes indicate differential siRNA abundance along maize chromosomes using perfectly mapped siRNA with unique position, ≤10, ≤100, and ≤1000 positions on maize genome, respectively, from outside to inside. They were preferentially enriched in high-density gene regions and chromosomal end regions but devoid in repeat-rich pericentromeric and centromeric regions. Red: high abundance; Yellow: medium abundance; Green: low abundance. Lane b: Chromosomal distribution of protein-coding genes and repeat sequences identified by Repeat-Mask software, and repeat sequences were highly enriched in centromeric and telomeric regions, which exhibited a negative correlation with gene density along chromosomes. Red: high proportion of repeats; Green: high proportion of genes; Yellow: relatively equal proportion of genes and repeats. Lane group c: Chromosomal distributions of siRNA loci identified by using the reads uniquely mapped, mapped with ≤10, ≤100 and ≤1000 positions respectively, from outside to inside, and the trend is similar to the siRNA abundance distribution. Red: high density; Yellow: moderate density; Green: low density. Lane d: Chromosomal distributions of imprinted genes (light gray) and imprinted siRNA loci (dark gray) on maize genome, which were distributed on all 10 chromosomes.