A maternal transcriptome bias in early Arabidopsis embryogenesis

After fertilization in animals, maternal mRNAs and proteins regulate development until the onset of zygotic transcription. In plants, the extent of maternal regulation of early embryo development has been less clear: two hybrid combinations of rice zygotes have a strong maternal transcript bias, zygotes of a third rice hybrid produced by gamete fusion show a small percentage of maternally biased genes, while Arabidopsis Col/Cvi and Col/Ler hybrid embryos display symmetric and asymmetric parental genome activation, respectively. Here, we explore parent-of-origin transcriptome behavior in the Arabidopsis Col/Tsu hybrid, which was previously shown to display maternal effects for embryo defective mutants indistinguishable from those of the reference ecotype, Col. Analysis of Col/Tsu transcriptomes revealed a reciprocal maternal bias in thousands of genes in zygotes and octant stage embryos. Several lines of evidence suggest that this transient maternal bias is due to preferential transcription of maternal alleles in the zygote, rather than inheritance of transcripts from the egg. Our results extend previous observations that parent-of-origin contributions to early embryogenesis differ between hybrids of Arabidopsis, show that the maternal genome plays a predominant role in early embryos of Col/Tsu, and point to a maternal transcriptome bias in early embryos of the Arabidopsis reference ecotype Columbia.