Seed size is a pivotal agronomic trait that links plant sexual reproduction and subsequent seedling establishment, and is affected by the timing of endosperm cellularization following endosperm proliferation after double fertilization. The molecular switch that controls the timing of endosperm cellularization has so far been largely unclear. Here, we report that the Arabidopsis TERMINAL FLOWER1 (TFL1) is a mobile regulator generated in the chalazal endosperm, and moves to the syncytial peripheral endosperm to mediate timely endosperm cellularization and seed size through stabilizing ABSCISIC ACID INSENSITIVE 5. We further show that Ras-related nuclear GTPases interact with TFL1 and regulate its trafficking to the syncytial peripheral endosperm. Our findings reveal TFL1 as an essential molecular switch for regulating endosperm cellularization and seed size. Generation of mobile TFL1 in the chalazal endosperm, which is close to maternal vascular tissues, could provide a hitherto-unknown means to control seed development by mother plants.

种子大小是关键的农艺性状，将植物的有性繁殖与随后的幼苗建立联系起来，并且受双重受精后胚乳增殖后胚乳细胞化时间的影响。到目前为止，还不清楚控制胚乳细胞化时间的分子开关。在这里，我们报告说拟南芥TERMINAL FLOWER1（TFL1）是一种在regulator子胚乳中产生的移动调节剂，它通过稳定ABSCISIC ACID INSENSITIVE 5转移到合胞体外周胚乳中，以适时地调节胚乳细胞化作用和种子大小。我们进一步表明，与Ras相关的核GTPAses与TFL1和调节其向合胞体周围胚乳的运输。我们的发现揭示了TFL1是调节胚乳细胞化和种子大小的重要分子开关。在靠近母体维管组织的带状胚乳中产生可移动的TFL1，可以提供迄今为止未知的方法来控制母本植物的种子发育。