Sequential gene activation and extensive gene imprinting during early embryo development in maize

The embryo is responsible for transmitting genetic information to the next generation. However, the underlying gene expression and gene imprinting during early embryo development remain largely elusive in maize. Using high-throughput RNA sequencing, we analyzed the allelic gene expression patterns of maize embryos from reciprocal crosses between inbred lines B73 and Mo17 at six time points (3 to 13 days after pollination). A total of 9532 genes were found to be differentially expressed in developmental stage, 3512 of 9532 genes were affected by cross direction. Co-expression analysis uncovered the sequential gene activations during maize embryo development. Further, we found 64 embryo strongly imprinted genes, including 57 maternally expressed imprinted genes (MEG) and 7 paternally expressed imprinted genes (PEG) in the maize embryo. Among them, 20 genes were continuously imprinted and 36 imprinted genes were newly identified. By applying In situ hybridization, we verified that six of the differentially expressed genes showed enriched transcription in the embryo. In addition, mutant analyses indicated that three of the imprinted genes displayed reduced embryo size. Therefore, our data shed new light on our understanding of the gene expression and gene imprinting in early maize embryo development, and suggested that imprinted genes are important for proper embryo development. Overall design: Embryos of 5DAP,7DAP,9DAP,11DAP,13DAP by manual, 3DAP and 5DAP by laser microdissection, and 5DAP endosperm of B73 X Mo17 and Mo17 X B73 were collected for RNA-seq analysis. Three biological replicates were performed for each sample.

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Meng D, Zhao J, Zhao C, Luo H, Xie M, Liu R, Lai J, Zhang X, Jin W