Research Highlights: Bacterial Protein Makes “Zombie” Plant

Photo courtesy of Whitney Cranshaw, Colorado State University,

Bacterial Protein Makes “Zombie” Plant

  • Obligate parasite is an organism that completes its life-cycle by exploiting a suitable host.
  • Some obligate parasites induce significant observable changes in their hosts which allows the parasites to be transmitted easily to other trophic levels.
  • However, the mechanisms underlying these changes are not well understood.
  • Researchers demonstrated how bacterial protein SAP05 from pathogenic phytoplasmas transmitted by insect take control of numerous developmental processes in plants.
  • Protein effectors are small molecules that selectively bind to a protein and modulate its biological activity.[2]
  • Phytoplasma is an obligate intracellular parasite of plant phloem tissue.[3]
  • Phytoplasma lacks cell wall and mainly transmitted by leafhoppers but also by plant propagation materials and seeds.[4]
  • These protein effectors make the host lifespan longer and promote witches’ broom-like growth of leaf and sterile shoots, parts colonized by phytoplasmas and vectors.
  • Normally, proteins not needed by plants are tagged with ubiquitin marking them as to be degraded.
  • A machinery called proteasome then degrades the tagged proteins for recycling.
  • SAP05 hijacks the protein degradation process and causes plant proteins involved in regulating growth to be degraded.
  • SAP05 binds to both regulatory protein and the proteasome facilitating the degradation of these protein.
  • Without these regulatory proteins, plant growth is affected which results in multiple vegetative shoot and tissue growth and suspension of plant aging.
  • Ubiquitin receptor is common among eukaryotic organisms; however, SAP05 does not bind to insect ubiquitin receptor.
  • Researchers pinpointed two amino acids in proteasome that are required to interact with SAP05.
  • If these two amino acids in plant protein are replaced with amino acids from insect protein instead, they no longer interact with SAP05 and prevents the witches’ broom abnormal growth.
  • The study highlights an effector protein that enables obligate parasitic phytoplasmas to promote an excess of growth development in their hosts.
  • The new findings offer the possibility of manipulating two amino acids in crops to provide long-lasting resilience against phytoplasmas and the effect of SAP05.

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