Zhang Yuexia, Zhang Yushi, Jiang Linjian, Li Zhaohu, Zhang Mingcai
College of Agronomy and Biotechnology, China Agricultural University, Beijing, China.
Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China.
Front Plant Sci. 2022 Jun 20;13:921245. doi: 10.3389/fpls.2022.921245. eCollection 2022.
Dodder ( spp.) species are obligate parasitic flowering plants that totally depend on host plants for growth and reproduction and severely suppress hosts' growth. As a rootless and leafless plant, excised dodder shoots exhibit rapid growth and elongation for several days to hunt for new host stems, and parasitization could be reestablished. This is one unique ability of the dodder to facilitate its success in nature. Clearly, excised dodder stems have to recycle stored nutrients to elongate as much as possible. However, the mechanism of stored nutrient recycling in the dodder shoots is still poorly understood. Here, we found that dodder is a carbohydrate-rich holoparasitic plant. During the dodder shoot development, starch was dramatically and thoroughly degraded in the dodder shoots. Sucrose derived from starch degradation in the basal stems was transported to the shoot tips, in which EMP and TCA pathways were activated to compensate for carbon demand for the following elongation according to the variations of sugar content related to the crucial gene expression, and the metabolomics analysis. Additionally, antioxidants were significantly accumulated in the shoot tips in contrast to those in the basal stems. The variations of phytohormones (jasmonic acid, indole-3-acetic acid, and abscisic acid) indicated that they played essential roles in this process. All these data suggested that starch and sucrose degradation, EMP and TCA activation, antioxidants, and phytohormones were crucial and associated with the dodder shoot elongation.
菟丝子属植物是专性寄生开花植物，完全依赖寄主植物生长和繁殖，并严重抑制寄主生长。作为一种无根无叶的植物，离体的菟丝子嫩枝会在数天内快速生长和伸长以寻找新的寄主茎干，从而重新建立寄生关系。这是菟丝子在自然界中得以成功生存的独特能力之一。显然，离体的菟丝子茎干必须循环利用储存的养分以尽可能伸长。然而，菟丝子嫩枝中储存养分循环利用的机制仍知之甚少。在此，我们发现菟丝子是一种富含碳水化合物的全寄生植物。在菟丝子嫩枝发育过程中，嫩枝中的淀粉显著且彻底地降解。基部茎干中淀粉降解产生的蔗糖被运输到嫩枝顶端，根据与关键基因表达相关的糖含量变化以及代谢组学分析，嫩枝顶端激活了糖酵解途径（EMP）和三羧酸循环（TCA）以补偿后续伸长所需的碳需求。此外，与基部茎干相比，抗氧化剂在嫩枝顶端显著积累。植物激素（茉莉酸、吲哚 - 3 - 乙酸和脱落酸）的变化表明它们在这一过程中发挥了重要作用。所有这些数据表明，淀粉和蔗糖降解、EMP和TCA激活、抗氧化剂以及植物激素对于菟丝子嫩枝伸长至关重要且相互关联。
