School of Chemistry and Biochemistry, The University of Western Australia, Crawley, 6009, WA, Australia.
Plant J. 2013 Oct;76(1):1-9. doi: 10.1111/tpj.12265. Epub 2013 Jul 25.
Strigolactone hormones are derived from carotenoids via carlactone, and act through the α/β-hydrolase D14 and the F-box protein D3/MAX2 to repress plant shoot branching. While MAX2 is also necessary for normal seedling development, D14 and the known strigolactone biosynthesis genes are not, raising the question of whether endogenous, canonical strigolactones derived from carlactone have a role in seedling morphogenesis. Here, we report the chemical synthesis of the strigolactone precursor carlactone, and show that it represses Arabidopsis shoot branching and influences leaf morphogenesis via a mechanism that is dependent on the cytochrome P450 MAX1. In contrast, both physiologically active Z-carlactone and the non-physiological E isomer exhibit similar weak activity in seedlings, and predominantly signal through D14 rather than its paralogue KAI2, in a MAX2-dependent but MAX1-independent manner. KAI2 is essential for seedling morphogenesis, and hence this early-stage development employs carlactone-independent morphogens for which karrikins from wildfire smoke are specific surrogates. While the commonly employed synthetic strigolactone GR24 acts non-specifically through both D14 and KAI2, carlactone is a specific effector of strigolactone signalling that acts through MAX1 and D14.
独脚金内酯激素通过 carlactone 衍生自类胡萝卜素，并通过 α/β-水解酶 D14 和 F-box 蛋白 D3/MAX2 起作用，抑制植物枝条分枝。虽然 MAX2 对于正常的幼苗发育也是必需的，但 D14 和已知的独脚金内酯生物合成基因则不是，这就提出了一个问题，即是否内源的、源自 carlactone 的典型独脚金内酯在幼苗形态发生中发挥作用。在这里，我们报告了独脚金内酯前体 carlactone 的化学合成，并表明它通过依赖细胞色素 P450 MAX1 的机制抑制拟南芥枝条分枝并影响叶片形态发生。相比之下，生理活性的 Z-carlactone 和非生理的 E 异构体在幼苗中表现出类似的微弱活性，并且主要通过 D14 而不是其同源物 KAI2 发出信号，以 MAX2 依赖但 MAX1 独立的方式。KAI2 对于幼苗形态发生是必需的，因此，这种早期发育使用了与独脚金内酯无关的形态发生素，而野火烟雾中的 karrikins 是其特异性替代物。虽然常用的合成独脚金内酯 GR24 非特异性地通过 D14 和 KAI2 起作用，但 carlactone 是独脚金内酯信号的特异性效应物，通过 MAX1 和 D14 起作用。
