Plants own an amazing high degree of developmental plasticity by regulating cell growth and division in response to internal and external signals. This plasticity is controlled by local maxima and minima of the signalling molecule, auxin. These are generated by the cell-to-cell movement of auxin, a unique process not yet described in non-plant organisms or for other hormones. This so-called polar auxin transport is thought to be mainly provided by the action of auxin exporters of the ABCB and PIN families. Interestingly, abcb loss-of-function mutants reveal a strong developmental phenotype, including a helical, non-handed disorientation of epidermal layers.
In my talk, I will address the morphological and molecular background for this “twisted syndrome” by dissecting the individual roles of ABCB proteins. It appears that all auxin-transporting ABCBs are regulated on the transport level by transient cis-trans isomerization of a conserved and diagnostic D/E-P motif. This catalytic activity is provided by PPIases, including the FKBP42, TWISTED DWARF1. Beside acting as PPIase, TWISTED DWARF1 functions also as a co-chaperone of HSP90 stabilizing ABCBs at the plasma membrane, indicating a dual role during ABCB regulation.
Our findings classify the TWISTED DWARF1-HSP90 module as a positive regulator of polar auxin transport providing plasticity to ABCB-controlled auxin transport and plant development.