Laboratories

Plant Symbiosis

Outline of Research and Education

Parasitic plants - major agricultural constrains in the world

Parasitic plants are able to parasitize the other plants and rely on their hosts for water and nutrients. Several parasitic plants in the Orobanchaceae family, such as Striga (Fig. 1) and Orobanche spp., cause enormous damage to world agriculture because they parasitize important crops and vegetables. We are investigating molecular mechanisms underlying plant parasitism using the model parasitic plants Phtheirospermum japonicum and weedy parasite Striga spp. By combining molecular genetic, cell biology and genomic approaches, we aim to understand the nature of parasitism and eventually develop novel control methods for weedy parasites.

Major Research Topics

Identification of genes involved in haustorium formation

Parasitic plants form specialized invasive organs called “haustorium”. The haustorium invades host roots, and eventually form a vasculature connection between the host and the parasite to assimilate host nutrients (Fig. 2). To identify the genes involved in haustorium formation, forward and reverse genetic tools in P. japonicum were established. Screening of P. japonicum mutants which lack haustorium formation and identification of the causal genes by next-generation sequencing (Fig. 3) will isolate the essential genes in the haustorium formation. Furthermore, the genes upregulated during haustorium formation will be reverse-genetically analyzed.

Plant-plant communication via small-molecular weight compounds

Parasitic plants recognize their hosts via small-molecular weight compounds secreted from the host plant (Fig. 4). For example, the obligate parasite Striga germinates in response to the plant hormone strigolactone, and its haustorium formation is induced by derivatives of cell wall lignin. However, some of our P. japonicum mutants do not respond to the known cell wall-derived chemicals, but are still able to form haustoria and parasitize hosts. We are trying to identify novel haustorium inducing compounds.

Comparative genomics of parasitic plants

Recent progress in next-generation sequencing technology enables us to acquire the complete genome sequence of any plant. We sequenced the whole genomes of Striga and P. japonicum. By examining these genome sequences, we found that parasitic plants have experienced evolutional events such as expansion of specific gene family and horizontal gene transfers from hosts. How did the plants obtain new genes, increase the copy numbers and eventually acquire a new trait? What is the genetic diversity among Striga species in Africa? We analyze genome evolution using bioinformatics tools.

References

  1. Cui, S. et al., Plant Physiol. in press 2016
  2. Conn, C., et al., Science, 349, 540-543, 2015
  3. Mutuku, M. et al., Plant Physiol. 168, 1152-1163, 2015
  4. Yoshida, S. et al., New Phytologist, 196, 1208-1216, 2012
  5. Yoshida, S. and Shirasu, K., Curr. Opin. Plant Biol, 15, 708-713, 2012
  6. Ishida, J., et al., PLos One, 6, e25802, 2011
  7. Yoshida, S. et al. Science, 328, 1128, 2010
  8. Yoshida, S. et al. New Phytologist, 183, 180-189, 2009
Sorghum field infested by Striga spp. (pink flowers) in Sudan.
Fig. 1 Sorghum field infested by Striga spp. (pink flowers) in Sudan.
Fig. 2 Obligate parasite Striga hermonthica (upper panels) and facultative parasite Phtheirospermum japonicum (lower panels). Photos of flowers (left), host invading parasitic plant root (middle) and cross section of haustorium (right). H: host, P: parasite. Arrowheads indicate haustoria.
Fig. 2 Obligate parasite Striga hermonthica (upper panels) and facultative parasite Phtheirospermum japonicum (lower panels). Photos of flowers (left), host invading parasitic plant root (middle) and cross section of haustorium (right). H: host, P: parasite. Arrowheads indicate haustoria.
Fig. 3 Identification of the mutant causal genes using a next-generation sequencer.
Fig. 3 Identification of the mutant causal genes using a next-generation sequencer.
Chemical communication between host and parasitic plants.
Fig. 4 Chemical communication between host and parasitic plants.
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