Researchers have gained another insight into the fascinating sophistication of the devil’s twine. The bizarre parasite not only steals the nutrients from its victims, but also their “mail”: it uses a messenger substance from the infected plants to coordinate its own flowering time with that of the victim. This enables the vampire to attack different types of plants and to use their “blood” optimally for themselves, explain the scientists.
They peacefully stretch their leaves into the sun and build biomass through photosynthesis – but that does not apply to all plants: the plant kingdom also includes completely unproductive representatives. They are so-called full parasites that feed completely on other plants. The genus Cuscuta is particularly rich in species: more than 200 species tap a wide range of host plants worldwide. The parasites known as devil’s thread or witch’s silk have neither roots nor leaves. They only develop flowers on their web-like structures, with which they cover their host plants. The vampire plants suck everything they need from their stems through special organs (haustoria). Here, too, the bizarre plants can damage plants, but losses in agriculture are caused by certain Cuscuta species, especially in southern countries.
Sucked out and spied on
Researchers have already gained interesting insights into the characteristics and genes of these amazing plants. In the course of their evolution, the parasites took over some genes from their victims, but lost others completely. An earlier study also showed that the plants connect to the internal communication network of their host plants via their suction organs. This can even offer the victims advantages: If a plant is attacked by insects, a signal transmission via the devil’s twine network also triggers defensive reactions in neighboring plants, which limit the infestation in the stand. Ultimately, however, this also benefits the devil’s twist, because healthy victims are easier to exploit.
In the current study, the researchers led by Jianqiang Wu from the Kunming Institute of Botany at the Chinese Academy of Sciences in Kunming have now devoted themselves to an interesting finding: Devil’s twine can evidently adjust the time of its flowering to the very different flowering times of its infested host plants. This seems astonishing for two reasons: In 2018, Wu and his colleagues sequenced the genome of the devil’s twine species Cuscuta australis and showed that many genes that control the flowering time are switched off in the plant’s genome. It would therefore have to be unable to activate its flower on its own. “The time of flowering is also controlled by leaves, because they receive the signals from the environment that are crucial for flowering and then produce the flowering signal FLOWERING LOCUS T (FT). So we wondered how the leafless parasite could control the timing of its flowering, ”says Wu.
The researchers investigated the suspicion that the devil’s twine hijacked the flowering signals circulating in its host plant and used it for its own flowering by investigating genetically modified host plants. In them, they have specifically modified the gene that controls the flowering signal. In this way, the scientists were initially able to prove that its activity actually controlled the time when the devil’s twine blossomed. They also coupled a green fluorescent protein (GFP) to the FT protein to make it visible in the plant tissues. In this way, they were able to show how the devil’s twine assimilates the flowering induction factor of the host plant. “We were able to show that the devil’s twine does not activate its flower itself, but that this is triggered by the FT proteins of the host plant,” sums up WU.
Timing is important
But why doesn’t the parasite regulate its flowering itself? As the researchers explain, it is beneficial for the parasite if it goes into the generative phase exactly synchronized with its respective victim. Because if it blooms much later, it misses the maximum yield for the formation of its own seeds, since the nutrient content of the victim decreases after flowering. The host may even die before the devil’s twine life cycle is complete. However, too early flowering would also be disadvantageous: because then the vampire would not have sucked long enough to be able to optimally develop seeds, the researchers explain.
Due to the loss of genes and the “outsourcing” of the flowering regulation, the devil’s twine was apparently able to optimally adapt to its broad host spectrum, which includes plants with very different flowering times. “Our study shows that it can even be beneficial for a living being to lose a control function,” concludes co-author Ian Baldwin from the Max Planck Institute for Chemical Ecology in Jena.
Source: Max Planck Institute for Chemical Ecology, Chinese Academy of Sciences Headquarters, specialist article: PNAS, doi: 10.1073 / pnas.2009445117