THE GENETIC AND EPIGENETIC MECHANISMS OF ENDOSPERM GROWTH AND SEED SIZE CONTROL IN ARABIDOPSIS THALIANA

Abstract

In flowering plants, seed is composed of endosperm and embryo, surrounded by maternal integuments. The endosperm is responsible for the supply of maternal nutrients to the embryo and plays a central role in endosperm growth and seed size determination. Endosperm growth is under control of the IKU pathway and several imprinted genes encoding subunits of the chromatin modifier Polycomb Group FIS. How these genetic and epigenetic pathways regulate the growth of endosperm remains unknown. Here, we show that the hormone cytokinin forms a spatio-temporal distribution pattern in the developing endosperm. This special pattern is due to the combination effect of cytokinin diffusion from one pole and degradation activity from another pole. The cytokinin degradation enzyme gene, CKX2, and consequence of cytokinin action are directly regulated by both IKU and FIS pathways. Our data show that the cytokinin pathway could play a central role in coordination of genetic and epigenetic control of endosperm growth and final seed size determination. In addition, by transcriptome analysis combined with bioinformatics analysis, we extend our finding from a single CKX2 gene to a large group of genes as targets of both the IKU pathway and epigenetic regulations. Thus, we propose a new gene network controlling seed growth.