How pathogen transforms “flower” into “leaf”? — Phytoplasma protein degrades floral transcription factors
March 17, 2014
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Normal flower of Arabidopsis thaliana (left), and phyllody-like flower induced by expression of phyllogen (right) © Shigetou Namba
Phytoplasmas are plant pathogenic bacteria associated with devastating damage to over 1000 plant species worldwide. Infected plants show a wide range of symptoms. Especially, plants exhibiting phyllody symptoms (formation of leaf-like tissues instead of flowers) have attracted much attention, and used to be traded with high commercial value. However, the molecular mechanisms of phyllody symptom development remain to be elucidated.
A research team headed by Professor Shigetou Namba in the Graduate School of Agricultural and Life Sciences at the University of Tokyo identified a novel gene family encoding for a phytoplasma-secreted protein “PHYLLOGEN”, and demonstrated that this protein is a pathogenic factor responsible for phyllody symptoms. His team found that PHYLLOGEN interacts with and degrades floral homeotic MADS-domain transcription factors that are conserved among flowering plants. This degradation of the MADS-domain transcription factors was dependent on the ubiquitin-proteasome pathway. The expression of floral development genes downstream of these transcription factors was actually disrupted in PHYLLOGEN-expressing transgenic plants. Moreover, PHYLLOGEN was genetically and functionally conserved among phytoplasmas. From these discoveries, Professor Namba’s team revealed the molecular mechanisms of phyllody symptom development for the first time.
PHYLLOGEN is expected to induce phyllody symptoms on many plants, as do phytoplasmas. Therefore, PHYLLOGEN will open a new frontier in breeding of unprecedented ornamental plants with green flowers of high commercial value. Moreover, PHYLLOGEN will be useful for increasing forage yield because it keeps plants in the vegetative phase. Development of inhibitors of PHYLLOGEN will also be helpful in the control of phytoplasma diseases.
Kensaku Maejima, Ryo Iwai, Misako Himeno, Ken Komatsu, Yugo Kitazawa, Naoko Fujita, Kazuya Ishikawa, Misato Fukuoka, Nami Minato, Yasuyuki Yamaji, Kenro Oshima, and Shigetou Namba, “Recognition of floral homeotic MADS-domain transcription factors by a phytoplasmal effector, phyllogen, induces phyllody,” The Plant Journal doi: 10.1111/tpj.12495.