The rapid stem elongation of the invasive weed Mikania micrantha in the forest understory is of vital significance for its successful invasion. To understand the physiological and molecular mechanisms for this process, here we comparatively investigated the physiological characteristics and transcriptome patterns of M. micrantha stem under low light (30%) and full light (100%) conditions. The results showed that M. micrantha stem had photosynthetic capacity, which was highly plastic to light intensities, constituting an indispensable part of the plastic response of M. micrantha to shading. M. micrantha had longer internodes, epidermal cells, and consequently longer stems under low light than full light conditions, which could proximally be attributed to phytohormone production and reduction of photoprotective substances as potential metabolic trade-off, as observed here under shading treatment. The transcriptome sequencing and qPCR verified the results from physiological investigation, and showed that under low light condition the expression levels of genes involved in photosynthesis (e.g. MmPsaA, MmPsbO1 and MmFd3) were generally down-regulated in comparison to full light condition, as were genes related to the photoprotective substances synthesis (e.g. MmCHS, and MmF3H1) and the negative regulators of phytohormone (e.g. MmAUX1, MmRR1 and MmGAI). It was concluded that the regulation of phytohormones and photoprotective substances are important material basis for the rapid elongation of M. micrantha stems with high plasticity, which facilitates the vine's invasiveness in the forest understory.

森林下层的入侵杂草Mikania micrantha的快速茎伸长对于其成功入侵具有至关重要的意义。为了了解此过程的生理和分子机制，在这里我们比较研究了在低光照（30％）和全光照（100％）条件下的M. micrantha茎的生理特征和转录组模式。结果表明，该菌具有光合作用能力，对光强具有高度的可塑性，是该菌对遮光的可塑性反应必不可少的部分。薇甘菊较弱光照条件下，其节间，表皮细胞更长，因此茎在较长的条件下比全光照条件下更长。这可以归因于植物激素的产生和光保护性物质的减少，这是潜在的代谢折衷，如此处在遮光处理下所观察到的。转录组测序和qPCR验证了生理学研究的结果，表明在弱光条件下，与全光条件下相比，光合作用相关基因（例如MmPsaA，MmPsbO1和MmFd3）的表达水平通常被下调。与光保护物质合成有关（例如MmCHS和MmF3H1））和植物激素的负调节剂（例如MmAUX1，MmRR1和MmGAI）。得出的结论是，调节植物激素和光保护性物质是快速延长具有高可塑性的米氏分支杆菌茎的重要物质基础，这有利于藤本植物在林下的入侵。