The polycomb repressive complex 2 (PRC2) is an important regulator of gene expression and development. PRC2 proteins are conserved in fungi, worm, fly, mammals and many plant species. In the model plant, Arabidopsis thaliana, PRC2 controls the development of the endosperm, the tissue in the seed that provides nutrients for the embryo. In monocots, like maize the endosperm constitutes the major volume of mature seeds and it the bulk of the edible kernel. Because the endosperm is a major constituent of seeds, an understanding of endosperm development has critical implications for agriculture. In many dicots, endosperm proliferation is the major determinant of mature seed size as has been shown in Arabidopsis thaliana and the related crop plant, canola. Endosperm proliferation in these dicots provides nutrient supplies for the subsequent embryo development. The aim of this award is to better understand how PRC2 regulates endosperm formation. This project augments the research and education missions of NSF. Researchers at different stages of their career development are trained in the fields of genetics, molecular biology and biochemistry. Students and trainees are mentored in the areas of career development, teaching, communication and interpersonal skills and professional development. Vigorous outreach activities foster scientific literacy and public engagement with science.
In angiosperms, double fertilization leads to the formation of a diploid embryo and a triploid endosperm. In many dicots, seed development involves an early endosperm proliferation to form a large embryo sac followed by a second phase in which the embryo grows to replace most of the endosperm at maturity. The expression of a few genes critical for endosperm proliferation such as MINI3 and IKU2 is activated after fertilization. At 4 days after pollination (DAP), the endosperm proliferation genes are repressed for a transition to embryo development. PRC2s play important roles in developmental phase transition. Of the three PRC2 complexes, Fertilization Independent Seed (FIS)-PRC2 silences the endosperm proliferation genes through histone methylation. None of the PRC2 subunits bind DNA in a sequence-specific fashion, and the knowledge of how PRC2s are recruited to a particular genomic locus is limited. MEA is the histone methyltransferase of the FIS-PRC2 complex and accumulates 4 DAP. Parallel to MEA accumulation, two AGAMOUS-LIKE (AGL) MADS-box genes are actively transcribed 4 DAP. The two AGL proteins bind the IKU2 promoter and interact with MEA. Therefore, the dynamic accumulation of MEA regulates the duration of endosperm proliferation, and the two AGLs are the readers to recruit MEA histone writer to the IKU2 and other potential loci. Their co-action facilitates a phase transition to embryo development. In this project, the dynamic MEA accumulation in relation to histone modification at the IKU2 locus and the recruitment of MEA to the IKU2 and other loci is explored.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
