Interspecies hormonal control of host root morphology by parasitic plants ($)

Parasitic plants draw nutrients from their hosts. Spallek et al. explored the molecular interaction between the parasitic plant Phtheirospermum japonicum (in the Orobranchaceae family) and the model plant Arabidopsis thaliana. They demonstrated movement of tracers from the host to the parasite through the xylem. They also showed that cytokinin hormone synthesis is induced in the parasite upon attachment, and that these hormones move into the host and direct changes in morphology. Specifically, the parasite induced a swelling in the host tissue (hypertrophy) above the site of attachment, which included an increase in the area of the xylem. Mutant analysis showed that hypertrophy required host cytokinin response genes but not cytokinin synthesis genes, indicating that it is a response to parasite-synthesized and transported hormones. Proc. Natl. Acad. Sci. USA 10.1073/pnas.1619078114