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Convergent evolution of strigolactone perception enabled host detection in parasitic plants

Science  31 Jul 2015:
Vol. 349, Issue 6247, pp. 540-543
DOI: 10.1126/science.aab1140

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How plant parasites evolved to find hosts

The seeds of parasitic plants need to be able to sense their host's presence to germinate at the correct time and in the correct place. This is done through the detection of plant hormones, strigolactones. However, the origin of this sensory system is unknown. Conn et al. investigated the diversity of strigolactone receptors in multiple lineages of parasitic plants and their close relatives. They found a greater copy number and accelerated evolution in parasitic plants as compared with nonparasitic relatives. Functional analyses of parasitic plant strigolactone receptors in transgenic Arabidopsis suggested that convergent evolution has occurred to allow the parasitic plants to detect their hosts.

Science, this issue p. 540

Abstract

Obligate parasitic plants in the Orobanchaceae germinate after sensing plant hormones, strigolactones, exuded from host roots. In Arabidopsis thaliana, the α/β-hydrolase D14 acts as a strigolactone receptor that controls shoot branching, whereas its ancestral paralog, KAI2, mediates karrikin-specific germination responses. We observed that KAI2, but not D14, is present at higher copy numbers in parasitic species than in nonparasitic relatives. KAI2 paralogs in parasites are distributed into three phylogenetic clades. The fastest-evolving clade, KAI2d, contains the majority of KAI2 paralogs. Homology models predict that the ligand-binding pockets of KAI2d resemble D14. KAI2d transgenes confer strigolactone-specific germination responses to Arabidopsis thaliana. Thus, the KAI2 paralogs D14 and KAI2d underwent convergent evolution of strigolactone recognition, respectively enabling developmental responses to strigolactones in angiosperms and host detection in parasites.

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