Integration of epigenetic and genetic controls of seed size by cytokinin in Arabidopsis

Abstract

The development of seeds in flowering plants is placed under complex interactions between maternal tissues, the embryo, and the endosperm. The endosperm plays a major role in the regulation of seed size. In Arabidopsis thaliana, endosperm size depends on the coordination of the genetic pathway HAIKU (IKU) with epigenetic controls comprising genome dosage, DNA methylation, and trimethylated lysine 27 on histone H3 (H3K27me3) deposition. However, the effectors that integrate these pathways have remained unknown. Here, we identify a target of the IKU pathway, the cytokinin oxidase CKX2, that affects cytokinin signaling. CKX2 expression is activated by the IKU transcription factor WRKY10 directly and promotes endosperm growth. CKX2 expression also depends on H3K27me3 deposition, which fluctuates in response to maternal genome dosage imbalance and DNA demethylation of male gametes. Hence, the control of endosperm growth by CKX2 integrates genetic and epigenetic regulations. In angiosperms, cytokinins are highly active in endosperm, and we propose that IKU effectors coordinate environmental and physiological factors, resulting in modulation of seed size.

Cell type-specific transcriptome analysis in the early Arabidopsis thaliana embryo

“…In the LCM dataset, however, all four genes were called present and at least weakly expressed within the suspensor. We also compared the different suspensor data sets for presence of previously described endosperm-specific genes (Kinoshita et al, 1999(Kinoshita et al, , 2004Luo et al, 2000;Kang et al, 2008;Li et al, 2013;Barthole et al, 2014). The LCM results show all six genes tested as present, whereas our data indicate that only two out of six are also at least weakly expressed in the suspensor (supplementary material Table S10) and those two were also detected in a RNA-seq transcriptome analysis (Nodine and Bartel, 2012).…”

Endosperm and Imprinting, Inextricably Linked

“…Seed formation requires extensive intergenerational and intertissue communication and coordination (Garcia et al, 2005;Ingouff et al, 2006;Ingram, 2010;Li et al, 2013;Xu et al, 2016). Angiosperm seeds consist of three genetically distinct entities: the diploid embryo, with one paternal and one maternal genome; the triploid endosperm, with two maternal and one paternal genome; and the protective integuments/seed coat, consisting of diploid maternal tissue from the previous generation (Fig.…”

Cross-Talk Between Sporophyte and Gametophyte Generations Is Promoted by CHD3 Chromatin Remodelers inArabidopsis thaliana

“…Perturbation of the machinery that contributes to gene expression in the endosperm can lead to alterations in seed size (Xiao et al 2006;Kradolfer et al 2013;Li et al 2013). To quantify the effect of PKL and/or PKR2 on seed size, we scored the mean seed areas of WT, pkl, pkr2, and pkl pkr2 seeds as described previously (Herridge et al 2011).…”

“…However, we found no evidence of differences in embryo development or seed set in pkl pkr2 plants relative to pkl plants ( Figure S5 and Table S6). Thus, rather than observing phenotypic enhancement by the loss of both paralogs, our data indicated that these traits are not PKR2 dependent.Perturbation of the machinery that contributes to gene expression in the endosperm can lead to alterations in seed size (Xiao et al 2006;Kradolfer et al 2013;Li et al 2013). To quantify the effect of PKL and/or PKR2 on seed size, we scored the mean seed areas of WT, pkl, pkr2, and pkl pkr2 seeds as described previously (Herridge et al 2011).…”