Imprinted gene expression in maize starchy endosperm and aleurone tissues of reciprocal F1 hybrids at a defined developmental stage

Imprinted gene expression in flowering plants predominantly occurs in the triploid endosperm of developing seed. However, endosperm is composed of distinct tissue types. For example, the maize ( Zea mays ) endosperm is constituted by two major tissues, starchy endosperm and aleurone. Previous studies in imprinted gene expression have generally assumed that the different tissues constituting endosperm would behavior the same, and hence have not examined them separately. Here, to examine parental-specific expression of imprinted genes in different parts of the seed, eight previously reported maize protein-coding imprinted genes were selected, and analyzed by cleaved amplified polymorphic sequence (CAPS) coupled with Sanger sequencing for transcripts from the various seed tissues collected at 18 days after pollination (DAP). The studied tissues included seed coat, embryo, starchy endosperm and aleurone, which were collected from a pair of reciprocal F1 hybrids produced by crossing inbred lines B73 and Mo17. Six of these eight analyzed imprinted genes showed the same imprinted expression pattern between the starchy endosperm and aleurone, but two showed imprinted expression only in the starchy endosperm. Comparison of the expression pattern of 20 selected imprinted genes in multiple seed tissues and vegetative tissues indicated that the majority (~ 75%) of these imprinted genes exhibited seed-specific or endosperm-specific expression. Our results also uncovered that imprinted genes have a high propensity to be alternatively spliced via intron retention in the developing embryo compared with the other tissues.