Many plants use environmental cues, including seasonal changes of day length (photoperiod), to control their flowering time. Under inductive conditions, FLOWERING LOCUS T (FT) protein is synthesized in leaves, and FT protein is a mobile signal, which is able to travel to the shoot apex to induce flowering. Dodders (Cuscuta, Convolvulaceae) are root- and leafless plants that parasitize a large number of autotrophic plant species with varying flowering time. Remarkably, some dodder species, e.g., Cuscuta australis, are able to synchronize their flowering with the flowering of their hosts. Detailed sequence inspection and expression analysis indicated that the FT gene in dodder C. australis very likely does not function in activating flowering. Using soybean host plants cultivated under inductive and noninductive photoperiod conditions and soybean and tobacco host plants, in which FT was overexpressed and knocked out, respectively, we show that FT-induced flowering of the host is likely required for both host and parasite flowering. Biochemical analysis revealed that host-synthesized FT signals are able to move into dodder stems, where they physically interact with a dodder FD transcription factor to activate dodder flowering. This study demonstrates that FTs can function as an important interplant flowering signal in host–dodder interactions. The unique means of flowering regulation of dodder illustrates how regressive evolution, commonly found in parasites, may facilitate the physiological synchronization of parasite and host, here allowing the C. australis parasite to time reproduction exactly with that of their hosts, likely optimizing parasite fitness.

许多植物利用环境因素，包括日长（光周期）的季节变化来控制开花时间。在诱导条件下，叶子中合成FLOWERING LOCUS T (FT)蛋白，FT蛋白是一种移动信号，能够传播到茎尖诱导开花。菟丝子（菟丝子、旋花科）是一种有根无叶的植物，寄生着大量具有不同开花时间的自养植物物种。值得注意的是，一些菟丝子物种，例如菟丝子，能够使其开花与其寄主的开花同步。详细的序列检查和表达分析表明，菟丝子C. australis中的FT基因很可能不具有激活开花的功能。使用在诱导和非诱导光周期条件下培养的大豆宿主植物以及分别过表达和敲除FT的大豆和烟草宿主植物，我们表明 FT 诱导的宿主开花可能是宿主和寄生虫开花所必需的。生化分析表明，宿主合成的 FT 信号能够进入菟丝子茎，与菟丝子 FD 转录因子发生物理相互作用，从而激活菟丝子开花。这项研究表明，FT 在寄主与菟丝子相互作用中可以作为重要的种间开花信号。菟丝子开花调节的独特方法说明了寄生虫中常见的回归进化如何促进寄生虫和寄主的生理同步，这里允许C. australis寄生虫与寄主精确地进行繁殖时间，可能优化寄生虫的适应性。