Cues of maternal and paternal origins interact to control seed development, and the underlying molecular mechanisms are still far from clear. Here, we show that TOPOISOMERASE Iα (TOP1α), UP-FRAMESHIFT SUPPRESSOR 1 (UPF1), and TRANSPARENT TESTA GLABRA2 (TTG2) gametophytically, biparentally regulate seed size in Arabidopsis. TOP1α and UPF1 are mainly expressed in antipodal cells, and loss of their function leads to ectopic TTG2 expression in these female gametophytic cells. We further demonstrate that TOP1α and UPF1 directly repress TTG2 expression through affecting its chromatin status and determine its relative expression in antipodal cells versus sperm cells, which controls seed size in a dosage-dependent and parent-of-origin-dependent manner. The molecular interplay among these three genes explains their biparental gametophytic effect during diploidy and interploidy reciprocal crosses. Taken together, our findings reveal a molecular framework of parental interaction for seed size control.

母本和父本起源的线索相互作用以控制种子的发育，其潜在的分子机制仍很不清楚。在这里，我们显示TOPOISOMERASEIα（TOP1α），UP-框架抑制物1（UPF1）和透明TESTA GLABRA2（TTG2）通过配子植物学双亲地调节拟南芥的种子大小。TOP1α和UPF1主要在对足细胞中表达，其功能丧失导致这些雌配子体细胞中异位TTG2表达。我们进一步证明TOP1α和UPF1直接抑制TTG2通过影响其染色质状态并确定其在对映体细胞与精子细胞中的相对表达，来控制种子的大小，而种子细胞以剂量依赖性和起源于母体的方式控制种子的大小。这三个基因之间的分子相互作用解释了它们在二倍体和倍体间互作期间的双亲配子体效应。综上所述，我们的发现揭示了父母控制种子大小的相互作用的分子框架。