Academy of Finland Research Fellow Ari Pekka Mähönen and his colleagues at
the University of Helsinki have demonstrated how PLETHORA proteins and plant
hormone auxin orchestrate root growth.

Auxin takes care of many aspects of root growth. If there is enough PLETHORA
in the root cells, auxin affects the rate of root cell division. If there is
little or no PLETHORA in the cells, auxin regulates cell differentiation and
elongation. In addition to this direct, rapid regulation, auxin also
regulates cell division, expansion and differentiation indirectly and slowly
by promoting PLETHORA transcription. This dual action of auxin keeps the
structure and growth of the root very stable. Mähönen and the research team
found that as PLETHORA levels gradually diminish starting from the root tip
upwards, the cell division, elongation, and differentiation zones are
created. This inner organization stays even if the growth direction of the
root changes.


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