Evolution, function, and regulation of genomic imprinting in plant seed development

Kin conflict in seed development: an interdependent but fractious collective

Seeds are complex structures that unite diploid maternal tissues with filial tissues that may be haploid (gametophyte), diploid (embryo), or triploid (endosperm). Maternal tissues are predicted to favor smaller seeds than are favored by filial tissues, and filial genes of maternal origin are predicted to favor smaller seeds than are favored by filial genes of paternal origin. Consistent with these predictions, seed size is determined by an interplay between growth of maternal integuments, which limits seed size, and of filial endosperm, which promotes larger seeds. Within endosperm, genes of paternal origin favor delayed cellularization of endosperm and larger seeds, whereas genes of maternal origin favor early cellularization and smaller seeds. The ratio of maternal and paternal gene products in endosperm contributes to the failure of crosses between different ploidy levels of the same species and crosses between species. Maternally expressed small-interfering RNAs (siRNAs) are predicted to associate with growth-enhancing genes.

MicroRNAs in metal stress: specific roles or secondary responses?

In plants, microRNAs (miRNAs) control various biological processes by negatively regulating the expression of complementary target genes, either (1) post-transcriptionally by cleavage or translational inhibition of target mRNA, or (2) transcriptionally by methylation of target DNA. Besides their role in developmental processes, miRNAs are main players in stress responses, including metal stress responses. Exposure of plants to excess metal concentrations disturbs the cellular redox balance and enhances ROS accumulation, eventually leading to oxidative damage or signaling. Plants modify their gene expression by the activity of miRNAs in response to metal toxicity to regulate (1) complexation of excess metals, (2) defense against oxidative stress and (3) signal transduction for controlling various biological responses. This review focuses on the biogenesis, working mechanisms and functioning of miRNAs in plants. In a final part, our current knowledge on the regulatory roles of miRNAs in plant metal stress responses is highlighted, and whether stress-regulated miRNAs have specific roles or are secondary consequences is discussed.