Using this system, downstream factors of TDIF signaling have been revealed.
Next, we isolated a factor that inhibits tracheary element differentiation and promotes cell division from this medium, which we named tracheary element differentiation inhibitory factor (TDIF).
Loss-of-function mutants of TDIF and its receptor exhibit a similar phenotype, in which procambial layers between xylem and phloem are absent due to inhibited procambial cell proliferation and the promotion of tracheary element differentiation from procambial cells.
The expression profiles of CLE41 and CLE44 and analysis of the cellular localization of TDIF indicate that TDIF is synthesized in the phloem and its neighboring cells and secreted toward procambial cells, in which TDR is specifically produced.
(17) The TDIF signal increases the expression of WOX4 in procambial cells in a TDR-dependent manner.
(13) In the absence of TDIF, GSK3s bind to the kinase domain of TDR and are inactivated.