Arabidopsis AGC3 kinases and PIN plasma membrane abundance

Gelderen, K. van (2017)

Doctoral Thesis

The plant hormone auxin plays a central role in the growth and development of plants.
Auxin acts in a concentration dependent manner and polar cell-to-cell transport of this
hormone determines its distribution in the tissues of plants. This polar auxin transport is
mediated by several families of auxin transporters, including the PIN FORMED (PIN) auxin
efflux carriers that determine the direction of transport by their polar localization at the
plasma membrane. The plasma membrane abundance and polarity of PINs (and thereby
of polar auxin transport) is regulated by their post-translational modification, of which
phosphorylation is best studied. PIN proteins in Arabidopsis consist of two transmembrane
domains separated by a ‘long’ (PIN1,2,3,4,6,7) or by a ‘short’ (PIN5,8) hydrophilic loop.
Phosphorylation of ‘long’ PINs in their central hydrophilic loop by the AGC3 kinases
PINOID, WAG1 and WAG2 triggers shootward (apical) or outer-lateral polarity. The AGC1-
type D6 kinases also phosphorylate the PIN hydrophilic loop, however this was reported
to result in auxin transport activation rather than subcellular polarity establishment.
Here we investigate the conservation and phylogeny of AGC3 and D6 kinases and their
phosphorylation sites in PINs from the earliest land plants to flowering plants. In early
land plants, many of the same proteins and conserved motifs can be found, however it is
in monocots and dicots that conservation of PIN phosphorylation by AGC3 and D6 kinases
is strongest. The expansion and increased conservation of AGC3 and D6 kinases and PINs
in later lineages such as monocot and dicot flowering plants, is in line with their important
role in the formation of reproductive organs and in the tropic growth responses that allow
plants to adapt to changes in their environment.

• AGC3 kinases
• PIN plasma membrane
• Arabidopsis
• D6 kinases
• PIN phosphorylation
• PINOID

• All authors: Gelderen, K. van
• Supervisor: Offringa, R.
• Committee: Spaink, H.P.; Hooykaas, P.J.J.; Friml, J.; Testerink, C.S.
• Qualification: Doctor (dr.)
• Awarding Institution: Institute of Biology, Science, Leiden University
• Date: 2017-07-06
• ISBN (print): 9789463322003