Zea mays Transcriptome or Gene expression
In angiosperms, the endosperm provides nutrients for embryogenesis or seed germination and is the primary tissue where gene imprinting occurs. To map the imprintome of the early developing endosperm in maize, we performed high-throughput transcriptome sequencing of the kernels at 0, 3, 5 days after pollination (DAP) and the endosperms at 7, 10, and 15 DAP produced from the B73 and Mo17 reciprocal crosses. We observed a gradual increase of paternal gene mRNAs in the 3- and 5-DAP kernels. In the 7-DAP endosperm, the majority of the tested genes reached a ratio of 2m:1p suggesting that paternal genes were nearly fully activated by 7 DAP. A total of 116, 234 and 63 imprinted genes exhibiting parent-specific expression were identified in the 7-, 10-, and 15-DAP endosperms, respectively. The highest amount of paternally expressed genes (PEGs) was found at 7 DAP mainly due to the significantly deviated parental allele expression ratio of these genes at this stage, while nearly 80% of the maternally expressed genes (MEGs) were specific to 10 DAP which were primarily attributed to the sharply increased expression levels compared to the other stages. GO enrichment analysis of the imprinted genes indicated the 10-DAP-specific MEGs were involved in the nutrient uptake and allocation through auxin signaling pathway in the maize endosperm coincident with the endosperm developmental stage associated with the beginning of starch and storage protein accumulation Overall design: The unpollinated kernels (0 DAP), the kernels of 3, 5 DAP and endosperms of 7 10, 15 DAP from the B73 and Mo17 reciprocal crosses were used to perform high-throughput sequencing using the Illumina HiSeq2000 platform