Activation of paternal siRNA loci in developing maize kernels and endosperms. a. Plot of the maternal reads versus the paternal reads of siRNA loci during different developmental stages. Paternally derived siRNAs were observed in the 3- and 5-DAP kernels, albeit at low abundance. The ratio of parental siRNA loci expression is likely to reach 2 m:1p in the 7-DAP endosperm. The expression level of paternally expressed siRNAs (y axis) and maternally expressed siRNAs (x axis) are represented by the log2-transformed sum of the paternally- and maternally-derived reads in the reciprocal crosses, respectively. Blue (low), yellow (medium) and red (high) represent the relative densities of the siRNA loci at different expression levels. b. Number of siRNA loci and counts of parental reads derived from the siRNA loci during the three developmental stages of the endosperm. DAP: days after pollination.