Self-restricting parasites
For parasitic plants it is a disadvantage if they all latch on the same host. Now Swedish and Japanese researchers show in PNAS that some parasitic plants at least can control this.
Worldwide there are lots of parasitic plants. Plants that latch on and infect a host plant so they can siphon off nutrients. In this regard it is a disadvantage for parasitic plants to latch on the same host. But up till now not much was known if parasitic plants control their numbers like symbionts do. This the researchers decided to investigate.
Doing so led to the finding that Phtheirospermum japonicum parasites that got to an already infected plant had less chance of successful latching on. How later they arrived, how smaller their change of success.
Cytokinin from Phtheirospermum japonicum halts late arriving parasites
Subsequently the researchers searched for the signal that reduces the chance of success for the late arrivals. For this, they analysed which genes were activated in Phtheirospermum japonicum after infecting its host. Which it turned out to be mostly genes involved in the production of the hormone cytokinin.
With help of a cytokinin biosensor the researchers subsequently see that the host plant has more cytokinin in its roots above the infection site and in its shoots. In addition, the researchers noticed that when they applied cytokinin locally on the roots, that this inhibited the infection by Phtheirospermum japonicum.
The cytokinin signal is only traveling to the shoot, but not to other roots of the infected plant. Still these roots are less infected by Phtheirospermum japonicum after a first infection. Therefore, the researchers suspect that the plant converts the cytokinin signal in the shoot before sending the signal back to the roots. What this new signal is, the researchers still need to find out.
Literature
A. Kokla, M. Leso, J. Šimura, C. Wärdig, M. Hayashi, N. Nishii, Y. Tsuchiya, K. Ljung, & C.W. Melnyk (2025) A long-distance inhibitory system regulates haustoria numbers in parasitic plants. Proc. Natl. Acad. Sci. U.S.A. 122 (8) e2424557122, https://doi.org/10.1073/pnas.2424557122
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