Graduate School of Agriculture, Ehime University, Matsuyama 790-8566, Japan; Japan Science and Technology, PRESTO, Kawaguchi 332-0012, Japan.
Center for Bioscience Research and Education, Utsunomiya University, Utsunomiya 321-8505, Japan.
Curr Biol. 2022 Aug 22;32(16):3601-3608.e3. doi: 10.1016/j.cub.2022.06.047. Epub 2022 Jul 14.
Plants have evolved elaborate mechanisms to detect neighboring plants, which typically involve the perception of "cues" inadvertently produced by the neighbor. Strigolactones are hormonal signaling molecules that are also exuded into the rhizosphere by most flowering plant species to promote arbuscular mycorrhizal symbioses. Since flowering plants have an endogenous perception system for strigolactones, strigolactones are obvious candidates to act as a cue for neighbor presence, but have not been shown to act as such. To test this hypothesis in rice plants, we quantified two major strigolactones of rice plants, orobanchol and 4-deoxyorobanchol, in root exudates by using LC-MS/MS (MRM) and examined feedback regulation of strigolactone biosynthesis and changes in shoot branching phenotypes in rice plants grown at different densities in hydroponics and soil culture. We show that the presence of neighboring plants, or greater root volume, results in rapidly induced changes in strigolactone biosynthesis, sensitivity, and exudation and the subsequent longer-term changes in shoot architecture. These changes require intact strigolactone biosynthesis in neighboring plants and intact strigolactone signaling in focal plants. These results suggest that strigolactone biosynthesis and exudation in rice plants are driven by supra-organismal environmental strigolactone levels. Strigolactones thus act as a cue for neighbor presence in rice plants, but also seem to act as a more general root density-sensing mechanism in flowering plants that integrates soil volume and neighbor density and allows plants to adapt to the limitations of the rhizosphere.
植物已经进化出了精细的机制来探测邻近的植物，这通常涉及到对邻居无意中产生的“线索”的感知。独脚金内酯是一种激素信号分子，大多数开花植物物种也会将其分泌到根际中，以促进丛枝菌根共生。由于开花植物具有内源性的独脚金内酯感知系统，独脚金内酯显然是作为邻居存在的线索，但尚未证明其具有这种作用。为了在水稻植株中验证这一假设，我们使用 LC-MS/MS（MRM）定量测定了水稻植株中的两种主要独脚金内酯，orbanchol 和 4-去甲独脚金内酯，在根分泌物中的含量，并在水培和土壤培养中研究了不同密度下生长的水稻植株中独脚金内酯生物合成的反馈调节和芽分枝表型的变化。我们表明，邻近植物的存在或更大的根体积会导致独脚金内酯生物合成、敏感性和分泌的快速诱导变化，以及随后对芽结构的长期变化。这些变化需要邻近植物中完整的独脚金内酯生物合成和焦点植物中完整的独脚金内酯信号转导。这些结果表明，水稻植株中的独脚金内酯生物合成和分泌是由超机体环境独脚金内酯水平驱动的。因此，独脚金内酯在水稻植物中作为邻居存在的线索，但在开花植物中似乎也作为一种更普遍的根密度感应机制，整合土壤体积和邻居密度，使植物能够适应根际的限制。
