Abstract
The protein IDN2, together with the highly similar interactors FDM1 and FDM2, is required for RNA-directed DNA methylation (RdDM) and siRNA production. Epigenetic regulation of gene expression is required to restrict cell fate determination in A. thaliana ovules. Recently, three transcripts sharing high similarity with the A. thaliana IDN2 and FDM1-2 were found to be differentially expressed in ovules of apomictic Hypericum perforatum L. accessions. To gain further insight into the expression and regulation of these genes in the context of apomixis, we investigated genomic, transcriptional and functional aspects of the gene family in this species. The H. perforatum genome encodes for two IDN2-like and 7 FDM-like genes. Differential and heterochronic expression of FDM4-like genes was found in H. perforatum pistils. The involvement of these genes in reproduction and seed development is consistent with the observed reduction of the seed set and high variability in seed size in A. thaliana IDN2 and FDM-like knockout lines. Differential expression of IDN2-like and FDM-like genes in H. perforatum was predicted to affect the network of potential interactions between these proteins. Furthermore, pistil transcript levels are modulated by cytokinin and auxin but the effect operated by the two hormones depends on the reproductive phenotype.
Highlights
Apomixis defines a few plant reproductive strategies which permit the inheritance of the maternal genome without genetic recombination and syngamy
Despite the lower expression observed in anthers, ATIDN2 and as FACTOR OF DNA METHYLATION 1 (ATFDM1)-5 transcripts were detectable during male gametogenesis, exhibiting an overall decreasing trend
Ovule cell fate determination requires the expression of genes involved in posttranscriptional gene silencing (PTGS) mediated by sRNA [9,30,31,32,33]
Summary
Apomixis defines a few plant reproductive strategies which permit the inheritance of the maternal genome without genetic recombination and syngamy This reproductive strategy is characterized by the differentiation of functional embryos, either from a somatic cell of the ovule nucellus or from an unreduced female gametophyte. The development of unreduced functional gametes from unorthodox cell precursors (i.e., different from the meiotically reduced functional megaspore) is a defining characteristic of a subset of reproductive strategies known as gametophytic apomixis (for reviews on apomixis, see References [1,2]) Among these strategies, the aposporous type of apomixis is characterized by the differentiation of functional embryo sacs (ESs) from somatic cells of the ovule. Results have shown that epigenetic regulation of gene expression by either DNA methylation or posttranscriptional gene silencing (PTGS)
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