Signaling pathways of seed size control in plants.

Seed size is one of the most important yield traits in plants. In angiosperms, a mature seed consists of the embryo, the endosperm and the seed coat, which develop from the zygote, the fertilized central cell and the maternal integuments, respectively. Seed size is therefore coordinately controlled by the growth of maternal and zygotic tissues. Several signaling pathways that determine seed size by influencing the endosperm and/or maternal tissue growth have been identified, including the IKU pathway, the ubiquitin-proteasome pathway, G-protein signaling, the mitogen-activated protein kinase signaling pathway, phytohormones and transcriptional regulatory factors. The functions of several seed size regulators are conserved in Arabidopsis and rice; therefore it is promising to convert basic research on seed size into practical applications in crops. In this review, we summarize recent research progress on seed size control, with particular emphasis on the genetic and molecular mechanisms of several newly identified regulators of seed size in Arabidopsis and rice.