Apomixis is a special process of reproduction through seeds that is different from sexual reproduction. Kentucky bluegrass (Poa pratensis) is a natural apomictic species and the genetic control of its apomixis is complicated and not completely clear. Thus, investigating natural apomixis mechanisms in Kentucky bluegrass would provide a better understanding of plant reproduction and provide clues as to how modifications of sexual reproduction helped various species adapt to different environments or different ploidies. We report the results of cytoembryological observation of the ovaries, changes in endogenous hormone contents and a global gene expression analysis of wild Kentucky bluegrass germplasm materials in Gansu province, China, exhibiting significant differences in apomictic rates to identify the genes, biological processes, and molecular functions related to apomixis. The results suggested that Kentucky bluegrass exhibited mainly facultative apospory, and the ZT content of LN was significantly higher than that of GN at all four developmental stages, and the IAA content of LN was significantly lower than that of GN at the first two stages. The most important result was that there were 5400 differentially expressed genes between the two genotypes, including 2476 downregulated and 2823 upregulated genes at four stages of reproductive development. Further analysis of the gene functions, pathways, expression patterns, and transcription factors showed that the occurrence of apomixis in Kentucky bluegrass was related to changes in the time- and space-related expression of genes associated with sexual reproduction, which led to disordered sexual reproduction and the production of offspring by apomixis. At the transcriptional level, the genesis and development of apomixis were regulated by transcription factors, as well as the co-expression of many genes associated with disordered meiosis, hormone signaling/response genes, embryonic development, and epigenetics. We verified 21 genes by q-PCR. The expression results were basically consistent with the transcriptome expression profile, indicating that the transcriptome was reliable. The results of this study may provide a more comprehensive understanding and a basic for the identification of candidate genes to reveal the mechanism of occurrence and development of apomixis in Kentucky bluegrass.

Graphical Abstract

In wild germplasm materials of Kentucky bluegrass in Gansu Province of China, the genesis and development of apomixis were regulated by transcription factors, as well as the co-expression of many genes associated with disordered meiosis, hormone signaling/response genes, embryonic development, and epigenetics.